organic crop production · 2005-12-05 · organic crop production organic crop. 123 research...

ORGANIC CROP

PRODUCTION

ORGANIC CROP

PRODUCTION

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Research indicates that long-vined, rapidly developing peavarieties were morecompetitive than shortervined cultivars. Leaf typemight be expected to make adifference, but studies atMorden did not find anadvantage to leafier varietiescompeting with wild

mustard. Pea cultivar(tall, leafy Century; tall semi-leafless Tipu; short leafyExpress) had no effect on

grassy weed populations.

Semidwarf winter wheatvarieties resulted in a 14-30%greater yield reduction fromdowny brome (

) than did taller

cultivars. Winter wheat wasmore effective in suppressingquack grass than tall or semi-

dwarf spring wheats.Research is currentlyunderway at the University ofSaskatchewan to develop oatcultivars with more weedcompetitiveness. Recentlydeveloped leafy forage oatgenotypes have been found tobe more competitive withwild oat than conventionalmilling or feed oat

genotypes.

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Bromustectorum

Perennial crops such as crestedwheatgrass, brome, sweet clover andalfalfa can be very competitive withannual weeds by eliminatingtillage’s stimulatory effect on annualweed seeds. Perennial crops can alsooffer competition against perennialweeds that lasts beyond the annual

crop season. Crested wheatgrassis more competitive than other

forages.

Each crop has many differentcultivars or cultivated varieties.Several major crops have traitvariability that affect competitive

ability. In the past, crop breedingprograms placed relatively littleemphasis on developing superiorcultivars for growth under weedy

conditions, but this is changing.

A test of 250 wheat varieties inAustralia showed that old standardvarieties (those released between1880 and 1950) suppressed weedsmore than most of the currentvarieties. Strongly competitivegenotypes had high early biomassaccumulation, large numbers oftillers, and were tall with extensive

leaf display. Yield differences inweedy conditions were not foundwhen herbicides were used. Tallercultivars had fewer weeds thanshorter cultivars. Cultivars alsodiffered in the dormancy of wheatseeds and thus, in the number ofvolunteer wheat plants in

subsequent years.

In a study of eight wheat cultivars atScott and Saskatoon, CDC Merlin,AC Minto and Columbus werefound most competitive, andGenesis and Oslo least competitivewith weeds. Spring spelt was themost competitive wheat in tests withmodel weeds (crop plants used to

simulate weeds).

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Problem

Background

Crops inevitably grow in relationship withweeds. Crops and weeds compete with eachother for limited resources, such as nutrients,light, water, space. How can this competitiverelationship be managed to give the advantageto the crop?

Competitive ability can be viewed twodifferent ways: ability to tolerate competition(maintain yield in the presence of weeds) andability to suppress weeds. Studies indicate thatthe competitive aspects of tolerance and

suppression may be correlated. Factors thatincrease competitive ability include rapidgermination, early emergence, seedling vigour,rapid leaf expansion, number of stomates, rapidcanopy development, plant height, early root

growth, and extensive root systems.

Crops differ in competitive ability with

weeds. In general, barley is more competitivethan spring rye. Both are more competitivethan wheat or oat, and flax is less competitive.Durum wheats are less competitive than spring

or winter wheat. Wheat is considered morecompetitive than pea, and then in order ofdecreasing competitive ability, pea, potato,

soybean, flax, and bean. Most pulse crops,like lentil, are poor competitors. Canola offerspoor competition to weeds in the seedlingstage, but can compete well once it becomes

established.

Fall sown crops such as winter wheat and fallrye offer excellent early season competition,and do not require spring cultivation. Thesecrops are especially effective at competing withspring germinating annual weeds such as wildoat or green foxtail. Fall sown crops also allowpartial fallow after harvest, for further weedcontrol. Greenfeed or silaging annual graincrops can be used as a partial fallow

replacement. Two years of harvesting barleyfor silage at an early stage (heads fullyemerged) reduced wild oat densities to levels

similar to wild oat herbicide applications.

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9-1 Growing a competitive crop – first step in weed control

– B. Frick, E. Johnson - Scott Research Farm

RESEARCH REPORT 2002

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Differences among cultivarsdepend on the entire croppingenvironment, not just thepresence of weeds. Forinstance, in years withaverage or below averagemoisture, a semi-leafless peacultivar seeded at reducedrates lost more to competitionwith wild mustard than did aleafy cultivar, and the semi-leafless cultivar lost more tocompetition when it wasseeded at low rates than whenit was seeded at high rates.Under drought conditions,wild mustard interferencecaused greater yieldreductions in the leafycultivar compared to the

semi-leafless cultivar.

Competitive ability variesamong crops and amongcultivars. Crops generallyare most competitive if theyhave vigorous growth,especially at stages whenweeds are emerging.Competitive ability isdetermined by characteristicsof both crop and weed, andalso by their environment.

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Conclusions

References1

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Lemerle, D., B. Verbeek, R.D. Cousens and N.E. Coombes. 1996. The potential for selectingwheat varieties strongly competitive against weeds. Weed Research. 36: 505-513.

Wyse, D.L. 1994. New technologies and approaches for weed management in sustainableagriculture systems. Weed Technology 8: 403-407

Pavlychenko, T.K. and J.B. Harrington. 1934. Competitive efficiency of weeds in cereal crops.Can. J. Res. 10: 77-94.

Swanton, C.J. and S.F. Weise. 1991. Integrated weed management: the rationale and approach.Weed Technology. 5: 657-663.

Dew, 1978 as cited by J.T. O'Donovan and M.P. Sharma. 1983. Wild oats competition and croploss. Wild Oat Symposium: Proc. Vol 1, p. 27. A.E. Smith, ed. University of Regina, CanadianPlains Research Center: Regina

Van Heemst, H.D.J. 1985. The influence of weed competition on crop yield. AgriculturalSystems 18: 81-93

Foster, K. 1996. FARMFACTS. Organic Crop Production: Weed Management. SustainableProduction Branch, Saskatchewan Agriculture and Food.

Anonymous. 1994. Practical Crop Protection. Weeds, Insects, Diseases. Alberta AgricultureFood and Rural Development Publishing Branch.

Harker, K.N. and K.J. Kirkland. 1999. Barley silage reduces wild oat ( ) populations.Proceedings of the 1999 Expert Committee on Weeds Annual Meeting. Expert Committee on

Weeds. Ottawa, ONT. 151 pages.

Ashford, R. 1975. Weed problems in rotations in extending crop rotations in Saskatchewan.Proceedings of the Soil Fertility Workshop. Extension Div. Univ. Of Sask. Pub. # 268.

Pavlychenko, T.K. and L.E. Kirk. 1946. Crested wheat grass helps in the control of perennialweeds. Univ. Of Sask. Agricultural Extension. Bull. # 120.

Liebman, M. 1988. Organic and low herbicide approaches for weed management. Proc.Bioregional Farmer/Scientist Workshop in Organic Agriculture (Maine & Maritime Provinces1988). D. Patriquin, ed. Fredricton, New Brunswick.

Wicks, G.A., P.T. Nordquist, G. E. Hanson and J.W. Schmidt. 1994. Influence of winter wheat(Triticum aestivum) cultivars on weed control in Sorghum (Sorghum bicolor). Weed Science 42:27-34.

Hucl, P., F.A. Holm, K.J. Kirland and E.N. Johnson. 1997. Spring wheat cultivars that differ incompetitive ability. SCAGPA Farm Based Program Report to North West Green Plan Committee.6 pages.

Saskatchewan Pulse Crop Development Board. 1995. Pulse Production Manual. SaskatchewanAgriculture and Food.

Townley-Smith, L. and A.T. Wright. 1994. Field pea cultivar and weed response to crop seedrate in western Canada. Can J. Plant Sci. 74: 387-393.

Loeppky, H.A. and D.A. Derksen. 1994. Quackgrass suppression through crop rotation inconservation tillage systems. Canadian Journal of Plant Science 74: 193-197.

Shirtliffe, S.J. and B. Rossnagel. 1999. Differential competitive ability of tame oat genotypeswith wild oat. Proceedings of the 1999 Expert Committee on Weeds Annual Meeting. ExpertCommittee on Weeds. Ottawa, ON 151 pages.

Wall, D.A., G.H. Friesen and T.K. Bhati. 1991. Wild mustard interference in traditional andsemi-leafless field peas. Can. J. Plant Sci. 71: 473-480.

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Funding

Further information

– Canada-Saskatchewan Agri-FoodInnovation Fund

–Eric JohnsonTel: 306-247-2011Fax: 306-247-2022E-mail: [email protected]


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9-2 Using allelopathic and cover crops to suppress weeds

– B. Frick, E. Johnson - Scott Research FarmProblem

Background

How can allelopathy and cover crops be usedto suppress weeds?

Allelopathy in plants is the production ofcompounds that inhibit the growth of otherplants. It may be direct, by living plants, orindirect through the products of plantdecomposition. Allelopathy may be mediated

by micro-organisms. It is a challenge toseparate the effects of resource competitionand alleopathy. Resource competition occurswhen one plant utilizes a necessary resourcefrom a habitat, and excludes access fromneighboring plants. In plant-plant interactions,allelopathy is generally used to denote theprocess by which plants release phtyotoxiccompounds (allelochemicals) in the soilenvironment, resulting in a harmful effect on

neighboring plants.

Both crops and weeds have been found tocontain compounds that can be consideredallelopathic. These include crops such asbarley, oat, wheat, rye, canola, mustard species,buckwheat, red clover, white clover, sweet-clover, hairy vetch, creeping red fescue, tall

fescue, and perennial ryegrass. Thesecrops, in rotation, may suppress weeds insubsequent crops; however, these crops’ weedsuppression effects cannot be solely attributedto allelopathy. As with all other techniques,caution must be employed. Crops withallelopathic properties may suppresssubsequent crop growth.

Cover crops may be sown to protect soil fromerosion, for snow trapping or to increase soilorganic matter. When the cover crop fixesnitrogen or otherwise improves soil properties,it is often referred to as a green manure. Bothcover crops and green manures can have weedsuppressing qualities. They may shade theground, thus reducing temperature fluctuationand the weed seed germination that depends on

it. They may compete with weeds, and thusreduce their vigour, or they may haveallelopathic properties. Cereal cover cropswith a high C:N ratio may immobilize soilnitrogen allowing nitrogen-fixing crops to bemore competitive. Tillage to kill the covercrop will also suppress weeds.

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that of weeds, in part becausecrops generally have largerseeds. Water use by themulch crop is partially offsetby greater snow-trapping.

Allelopathic mulches havepotential problems as well asadvantages. They maydeplete moisture and immob-ilize nutrients, especiallynitrogen. Including rapidlydecomposing legume crops inthe mix helps alleviate the

latter problem. Theallelopathic effect mayinhibit germination of small-

seeded crops. Cover cropsmay be more effective whenyou eliminate tillage, toconcentrate residues more at

the soil surface.

Weed suppressing mulchesneed not be crop residues.Small areas of perennialweeds can be mulched withsubstances like manure. Youneed a substantial amount ofmanure for effective control -three feet or more deep, atleast four feet beyond thepatch. Other mulches: tarpaper or black polyethylene,and mulched wood. Mulchesmust be maintained for atleast one year for good weed

suppression. Check with acertifying agent which non-plant mulches are allowed.

Allelopathy is one plant’sproduction of chemicals thatsuppress another. Covercrops are sown for the soil,and may have potential as afallow substitute.

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Conclusions

Cover crops can be sown intoexisting crops. If so, the timingshould correspond to the time whenweeds no longer cause yield losses

(the end of the critical period).Cover crops may also be sown afterharvest, or in place of a fallow.Successfully established cover cropscan develop sufficiently densecanopies in the fall to interfere withgrowth of perennial and winterannual weeds. Most tests of covercrops involve fall or winter cerealssown in the late summer and killed

by herbicides the following spring.Research at Lethbridge found that awell established, vigorous fall ryecover crop that was killed byherbicides or tillage in the springsuppressed weeds for the remainder

of the fallow season. The covercrop protected the soil from erosionand provided about a 50% reductionin weed biomass in the fallcompared to bare fallow. The fallrye cover crop was particularlyeffective in reducing populations ofdandelion and Canada thistle.Wheat yields following the covercrop were equal to yields obtainedon bare fallow.

Fall seeded and spring tilled winterhardy rape substantially reducedlambs quarters and pigweed growthin a subsequent potato crop, andmay have suppressed nematodes

and diseases as well. Anotheralternative is to use species that arenot winter hardy. Tests withsorghum and oats showed weedsuppression. These tests showed lesseffect than those where a winterhardy crop was killed chemically in

the spring. Winter-killed covercrops form a mulch in the springthat further suppresses weed

establishment and growth.Mulches may suppress weeds, butthey are generally inadequate to

control perennial weeds. Cropsuppression is generally less than

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References1

Weston, L.A. 1996. Utilization of allelopathy for weed management inagroecosystems. Agronomy Journal 88: 860-866.

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Chou, C.H. 1999. Roles of allelopathy in plant diversity and sustainableagriculture. Crit. Rev. Plant Sci. 18: 609-636.

Liebman, M. 1988. Organic and low herbicide approaches for weedmanagement. Proc. Bioregional Farmer/Scientist Workshop in OrganicAgriculture (Maine & Maritime Provinces 1988) D. Patriquin, ed. Fredricton,New Brunswick.

Teasdale, J.R., C.E. Beste, and W.E. Potts. 1991. Response of weeds to tillageand cover crop residue. Weed Science 39: 195-199.

Boydston, R.A. and A. Hang. 1995. Rapeseed (Brassica napus) green manurecrop suppresses weeds in potato (Solanum tuberosum). Weed Tech 9: 669-675.

Ghersa, C.M., M.L. Roush, S.R. Radosevich, and S.M. Cordroy. 1994.Coevolution of agroecosystems and weed management. BioScience 44: 86-94.

Swanton, C.J. and S.F. Weise. 1991. Integrated weed management: therationale and approach. Weed Technol. 8: 403-407.

Wyse, D.L. 1994. New technologies and approaches for weed management insustainable agriculture systems. Weed Technology 8: 403-407

Moyer, J.F., R.E. Blackshaw, E.G. Smith, and S.M. McGinn. 2000. Cerealcover crops for weed suppression in a summerfallow-wheat cropping sequence.Can. J. Plant Sci. 80: 441-449.

Putnam, A.R., J. Defrank, and J.P. Barnes. 1983. Explotiation of allelopathyfor weed control in annual and perennial cropping systems. J. Chemical Ecology9: 1001-1010.

Thompson, H.N. 1916. Farm weeds and how to control them. Sask. Dept.Agr. Bull # 31

Funding

Further information


– Eric JohnsonTel: 306-247-2011 Fax: 306-247-2022E-mail: [email protected]


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should be destroyed bysubsequent tillage. Newplant growth should not beallowed to grow taller thanthree inches before being

tilled. Tillage should be nodeeper than required to do aneffective job. Shallow tillagewill concentrate rhizomes onor near the soil surface,resulting in a more uniformemergence and better control

from future tillage.

Tilled fallow is a manage-ment tool to be used withcaution. Extensive fallow forweed control has probablyled to the evolution of greaterdormancy in some weedspecies. Weed communitiesadapt to whatever practicesare applied consistently.Repeated cultivation isdetrimental to the soil, andpractices that reduce theintensity or extent of tillageshould be considered.

Summerfallow tillage can beused to reduce the seedbanksof annual weeds, and toattack persistent perennialweed problems. Tillage andfallow should both be usedcautiously, since they canresult in severe soil andenvironmental degradation.

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Conclusions

Fallow may also be used to controlperennials such as Canada thistle

and perennial sow-thistle. Withthese species, the first tillage shouldbe done at the bud stage. Foodreserves are at a low at this time,

and the tillage is most effective.Once tillage begins, it shouldcontinue each time the plant reachesa height of about three inches, untilfreeze up. This approach will starvethe root system and prevent it fromforming any food reserves. Theplants will enter winter in a veryweakened state and many of them

will not survive.

This late season tillage for perennialweed control may be used after anearly maturing crop, or in a partial

fallow situation. Appropriate cropsinclude sweet clover, early maturingbarley, fall rye, or oat cut for feed.Fall tillage after later maturing cropscan also be effective againstperennial weeds. Plants can bekilled by exposing the roots, iffreezing temperatures follow shortly

after tillage. Fall tillage reducesstubble and trash cover -- reducingsnow trapping. It also acceleratessoil erosion. So fall tillage shouldbe approached cautiously.

Quackgrass problems should behandled differently. Tillage tocontrol this weed depends onphysically damaging the rootsystem. In dry years, a cultivatorwith narrow spikes will be effective,as this drags roots and rhizomes tothe surface where they dry out anddie. In wet years or areas, the firsttillage operation should be with adisc implement that cuts therhizomes into small pieces. Eachsmaller rhizone section will try toestablish a new plant, which in turn

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Problem

Background

Fallow has traditionally played a large part inweed control strategies. What are theadvantages and disadvantages of thistechnique?

Fallow can be used as a weed control methodfor both annual and perennial weeds. It can beused to reduce the weed seedbank by allowingweeds to germinate, then killing them beforethey set seed. This is especially effective onweeds with short dormancy periods, such askochia, goat’s beard, hare’s ear mustard, Indianmustard, Russian thistle, cow cockle, greenfoxtail, downy brome, wild buckwheat or

foxtail barley. Some reduction is possible forweeds with longer dormancy, but some seedswill survive.

Three to six tillage operations may be requiredfor effective annual weed control during the

fallow year. An early start is recommended for

summerfallow tillage, perhaps by mid-May.Tillage operations should be as shallow aspossible to avoid bringing new weed seeds tothe soil surface. The initial operation shouldalways be the deepest with subsequent onesprogressively shallower. Tillage is mosteffective when the soil surface is dry and airtemperature high. Tilling small seedlings whenthe soil surface is moist will usually producepoor results, as many of the seedlings are

transplanted rather than being killed.

Fall tillage is an alternative to fallow tillagethat can be used to destroy winter annual andbiennial weeds. On weeds that over-winter,fall tillage is more effective than spring tillage.Fall tillage may encourage some summerannual weeds to germinate and most of thesewill be winter-killed. However, tillage alsoburies weed seeds that may become dormant,acting as a reserve for later years. Fall tillageshould be shallow (less than four inches) to

avoid deep burial of weed seeds. Alternatingintensive tillage during fallow years withcropping and spring and fall tillage can be used

to reduce severe perennial weed problems.

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References1

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Chepil, W. S. 1946. Germination of weed seeds II: The influence of tillagetreatments on germination. Sci. Agr. 26: 347-357.

Molberg, E.S., E.V. McCurdy, A. Wenhardt, D.A. Drew and R.D. Dryden.1967. Minimum tillage requirements for summer fallow in Western Canada.Can. J. Soil Sci. 47: 211-216.

Canada. Experimental Farm, Scott, Sask. 1954. Progress Report 1948-1953.

Foster, K. 1996. FARMFACTS. Organic Crop Production: Weed Management.Sustainable Production Branch, Saskatchewan Agriculture and Food

Keys, C.H. and D. E. Forsburg. 1954. Tillage and cropping methods for thecontrol of toadflax, Linaria vulgaris. National Weed Committee (WesternSection) Research Report.

Pavlychenko, T.K. and L.E. Kirk. 1946. Crested wheat grass helps in thecontrol of perennial weeds. Univ. of Sask. Agricultural Extension Bull #20.

Subcommittee on Weeds, Committee on Plant and Animal Pests, AgriculturalBoard, National Research Council. 1968. Weed control, principles of plant andanimal pest control, volume 2. Publ. 1597. National Academy of Sciences,Washington, D.C.

Results of experiments 1931-1936 inclusive. 1938. Experimental sub-sttion,Regina, Saskatchewan. Dominion of Canada Dept. Of Agriculture, DominionExperimental Farms.

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BioMal is a bioherbicide thatcontains viable spores of afungus,

that infects round-leavedmallow. Tests indicate that itcan have a significant effecton the weed population. Itcurrently is not available onthe market.

The Saskatoon ResearchCenter is a leader in researchand developing inundativebiocontrol agents. Severalpromising agents have beenidentified and are beingdeveloped to control weedssuch as wild oat, greenfoxtail, dandelion, andscentless chamomile.Developing a bioherbicide ischallenging since it is a livingorganism that must remainviable after application inorder to be effective.Researchers at the SaskatoonResearch Center aredeveloping novel deliverysystems for applyingbiocontrol agents.

Classical biocontrol agentsare available for a fewperennial weed species.Agents can be collected atprevious release sites wherethey are already established.These agents offer thepossibility of long-term, low-cost control. Inundativebiocontrol agents have notyet reached the farm gate, butthey have good potential.

Colletrotichumgloeosporoides f. sp. malvae,

Conclusions

Toadflax seed predatorsand

can bespread by placing infected toadflaxstems among flower stems at the

new site. Additional agents beingtested for toadflax control includethe stem boring weevil

, the root boring mothand the root

galling weevil .However, initial releases of

anddid not establish successfully inSaskatchewan.

The seed weevil hassuccessfully established on scentlesschamomile after initial releases in1992. The population is increasingover time and the weevil can reduceup to 40% of seed the plantproduces. Other biocontrol agentsreleased on scentless chamomileinclude a stem weevil

and a gall midge.Releases are currently beingmonitored for establishmentsuccess. Growers who want toobtain scentless chamomile seedweevils may contact SaskatchewanAgriculture and Food.

involvesapplying large quantities of acontrol agent (such as a fungalpathogen) to weeds in much thesame manner as a chemicalherbicide. Once an inundativebiocontrol agent is identified, itspropagules (eg. spores, mycelium)can be produced in large quantitiesthrough fermentation techniques.The ... “commercial feasibility tomass-produce viable, infective andstable propagules of the pathogen isa major requirement for developing

a bioherbicide”.

Brachypterolus pulicariusGymnaetron antirrhini

MecinusjanthinusEteobalea serratella

Gymnetron linariaeMecinus

janthinus Eteobalea serratella

Apion hookeri

Microplontusedentulus

Inundative biocontrol

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Problem

Background

Weeds are often introduced species inagricultural habitats. In their original habitats,they may have been less abundant, in partbecause their natural predators and diseasesreduced their vigour and they were incompetition with other species. How can weuse these biological methods of weed control?

of weeds is using living organismsto destroy weeds, or to inhibit their growth andability to compete with crops. Biocontrol isoften separated into two categories:introducing classical biocontrol agents, ofteninsects, and the increase and inundative use oforganisms, often disease agents.

introduces naturalpredators to weed populations. Classicalbiological weed control with insects involvesintroducing host-specific natural enemies fromthe target weed’s native range. Classicalbiocontrol has had good long-term success insome instances, particularly in rangeland. It isless commonly used in cropped land.Generally, the target weed is a long-livedperennial species that is especially difficult tocontrol by traditional means.

Nodding thistle is attacked by a weevil,introduced to Saskat-

chewan in 1968. Weevils may be gathered bycollecting about 500 infected nodding thistleseed heads in mid-August, and placing them innew stands. Several years are required for theweevil population to become established sothat it can effectively control the thistle.

Two insects, the black dot spurge beetle, and the copper spurge

beetle can be used asbiocontrol agents in leafy spurge. Larvae feedon spurge roots. The black dot spurge beetle ismore effective on high, dry and exposed sites,on coarse soils. In Alberta, redistribution ofbeetles is about 65% successful.Redistribution is accomplished by collecting

and releasing adult beetles.

Biocontrol

Classical biocontrol

Rhinocyllus conicus

Aphthona nigriscutisAphthona flava

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References1

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Harris, P. 1978. Biological control of weeds in Chemicals and Agriculture;Problems and Alternatives. Canadian Plains Proceedings 5. Canadian PlainsResearch Centre, University of Regina.

Anonymous. 1994. Practical Crop Protection. Weeds, Insects, Diseases.Alberta Agriculture Food and Rural Development Publishing Branch.

Wyse, D.L. 1994. New technologies and approaches for weed managementin sustainable agriculture systems. Weed Technology 8: 403-407.

Auld, B.A. and L. Morin. 1995. Constraints in the development ofbioherbicides. Weed Tech. 9: 638-652.

Funding –

Research coordination –

Canada-Saskatchewan Agri-Food Innovation Fund

Eric JohnsonTel: 306-247-2011 Fax: 306-247-2022E-mail: [email protected]

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used in green feed if cutbefore seed set. To controlperennial weeds, mowingmight be delayed until theonset of weed floweringwhen food reserves are at alow point. The weed willrespond by sending up newstems, further depleting itsreserves. Mowing at aboutthree week intervals canseverely weaken or even kill

the weeds.

Mowing is also important inconjunction with perennialforages. Mowing can beuseful in giving an advantageto perennial forages overweeds. By preventing annualweeds’ seed set, anddepleting reserves ofperennial weeds, mowingmay be the most importantcomponent of weed control inperennial crops.

Mowing, like tilling, caninterfere with beneficialcreatures. Delaying mowinguntil mid to late July canreduce nesting birds'

mortality. This fits well withperennial weed control, butmay compromise annualweed seed set prevention.

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Tillage is not appropriate in somesituations. Where risks of erosion orsalinization are high, avoidingtillage is important. In othercircumstances, tillage’s negativeeffects can be limited by carefulmanagement, or seeking alternativesthat reduce the need for tillage.

The type of tillage itself makes adifference. Some implements, suchas the Noble or Victory blades, thatleave stubble standing, will alleviatesome fall tillage risk. These twoequipment types are less effective incool wet conditions. Tilling atslower speeds can reduce theerosion potential.

The amount of tillage can belessened in various ways. You canleave uncultivated strips betweencultivated areas. Leaving strips mayalso help trap snow. Tilling weedypatches rather than entire fields mayalso reduce risk. If erodible knollshave few weeds, leaving the knollsuntilled will conserve residues andlimit erosion. Where fallow tillageis planned, black summerfallow canbe replaced with partial fallow, forinstance, after plowdown of anunderseeded crop, or mowing greenfeed.

Mowing, in place of tillage, can bean effective part of weed controlwhere tillage is undesirable. Doneearly enough, mowing may preventweed seed set. To be effective,mowing should be done beforeflowering, as many weeds can setseed very quickly after flowering,using the reserves left in the portionof cut stem that remains attached to

the flowers. Many weeds, such aswild oats or Russian thistle, can be

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Problem

Background

Tillage is often seen as the organic alternativeto chemical weed control. Tillage can be veryeffective at reducing weed populations, but canit be embraced as the solution to the weedproblem? What cautions are necessary?

Tillage should be considered an external input– it requires the expenditure of fossil fuels.Reducing tillage reduces dependence onlimited non-renewable resources. Springtillage loosens and dries soil, thus warming it.Tillage can pulverize soil, making it more

susceptible to erosion. Tillage reduces stubbleand trash cover, thus reduces snow trapping,and also accelerates soil erosion. Tillage alsospeeds decomposition and loss of organicmatter, and increases salinization. It increasesnitrogen volatilization to the atmosphere andpotential for nitrate leaching.

Tillage also affects life within the soil. It canreduce the survival of beneficial invertebrates,

soil microfauna and microflora. Tillagereduces the populations of weed-seed eating

carabid beetles and field crickets.

Tillage exposes soil and weed seeds to thelight. For some species, this triggersgermination. When cultivation was performedat night or if the implement was covered, weed

populations were reduced by up to 50%.Tillage places weed seeds in better contact withthe soil, also facilitating germination. In termsof weed control, deep tillage is a mixedblessing. It may bring up dormant seeds buriedin the soil, and bury other seeds for

later retrieval.

Tillage equipment may spread perennial plantparts throughout the field. In this way, a smallpatch can become a general problem. Tillagefavors some species over others, and thus isone of the management tools that can be used

to alter weed communities.

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ConclusionsEvery weed control techniquehas benefits and detriments.Non-chemical methods arenot automat-ically

environmentally friendly.Techniques can sometimes bealtered to reduce detrimentswithout greatly reducingbenefits. In developingeffective and efficient weedmanagement strategies,growers must consideradvantages, disadvantagesand limitations of all the toolsavailable.

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References1

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Ghersa, C.M. 1994. Coevolution of agroecosystems and weed management. BioScience44: 85-94.

House, G.J. and Brust, G.E. 1989. Ecology of low input, no-tillage agroecosystems. Agric.Ecosyst. Environm. 27: 331-345.

Jordan, V.W.L. 1992. Opportunities and constraints for integrated farming systems. Proc. 2nd

European Society of Agronomy Congress, Warwick University.

Brust, G.E. and House, G.J. 1988. Weed seed consumption in low-input soybeanagroecosystems by arthropods and rodents. Am. J. Alt. Agric. 3: 19-25.

Galagher, R.S. and J. Cardina. 1998. The effect of light environment during tillage on therecruitment of various summer annuals. Weed Science. 46: 214-216.

Yenish, J.P., J.D. Doll, and D.D. Buhler. 1992. Effects of tillage on vertical distribution andviability of weed seed in soil. Weed Sci. 40: 429-433.

Banting, J.D. 1977. Growth habit and control of wild oats. Canada Agriculture Publication1531 (Revised)

Ashford, R. 1978. Weeds and Their Control. Wascana Institute of Applied Arts and Sciences,Regina, Saskatchewan

Anonymous. 1994. Practical Crop Protection. Weeds, Insects, Diseases. Alberta AgricultureFood and Rural Development Publishing Branch.

Rasmussen, J., J. Ascard. 1995. Weed control in organic farming systems D.M. Glen, M.P.Greaves, H.M. Anderson, eds. Ecology and Integrated Farming systems. John Wiley and SonsLtd., Bristol, UK.

et al.

in

Funding – Canada-Saskatchewan Agri-FoodInnovation Fund

Further information – Eric JohnsonTel: 306-247-2011 Fax: 306-247-2022E-mail: [email protected]

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133

yield increases of 57 to300%. Benefits from inter-row cultivation were limiteddue to in-row weed growth.Most uncontrolled weedgrowth occurred in theuncultivated area adjacent toand within the crop row.Results

cultivation provided that

weed populations are low.Therefore, integration withother mechanical or culturalmethods may be required forsatisfactory results with inter-row cultivation.

Inter-row cultivation haspotential as means ofcontrolling late flushes ofweeds. It should not beconsidered a stand-aloneweed management techniquesince significant in-row weedgrowth may limit benefits.Future studies shouldinvestigate the potential ofinter-row cultivationconducted on the sameexperimental area over anumber of years to trulyevaluate its potential.

from this study areconsistent with researchconducted in other parts of theworld. A standard cultivatorwas not effective in controllingweeds in field bean due to

intra-row weed growth. Anin-row cultivator or rotaryhoeing prior to inter-rowcultivation was required toreduce weed populations tothat achieved by a herbicide.Another study foundsatisfactory results with inter-

row

1 0

11

Conclusions

inter-row cultivation. Inter-rowcultivation was conducted with amodified S-tine cultivator. Threetines were arranged in a deltaformation and fitted with 10-cmsweeps to fit between the crop rows.Cultivation depth was 2.5 to 3.0 cmand was adjusted to ensure that croprows were not covered by soil.

Cultivation speed was 3.5 km/hr .Experimental design was arandomized complete block withtreatments consisting of sequentialinter-row cultivations (1, 2, and 3cultivations) and an untreated check.We cultivated at field pea’s 6, 8, and10-node stages. Inter-rowcultivation before the six-node stagewould have resulted in too muchcrop burial. A herbicide treatedcheck was also included (seeded in22 cm rows). Data collectionincluded crop and weed density andbiomass, and crop yield.

Successive inter-row cultivationcaused a linear reduction in wildmustard density in both years.Those wild mustard plants thatremained produced as muchbiomass as plots where cultivationwas not done. Many weed speciesexhibit morphological plasticity inresponse to environmental variation

and density. Weeds can compen-sate for density changes so that totalbiomass per unit area is heldrelatively constant. Inter-rowcultivation had an erratic effect ongrass weeds' density and biomass.Field pea yield showed a linearresponse to successive inter-rowcultivation in both years. Responsemagnitude was greater under themore favorable growing conditionsin 1999. Inter-row cultivationimproved field pea yield by 33%and 78% for 1998 and 1999,respectively. However, herbicideapplication resulted in respective

-1

9

Major findings

Problem

Background

Study description

Some growers in western Canada haveconsidered using inter-row cultivation as analternative to herbicides. There has been littleresearch in western Canada on inter-rowcultivation in our commonly grown field crops.This study’s objective was to evaluate inter-row cultivation as an alternative weedmanagement system in field pea.

Inter-row cultivation is commonly used in row

crop production in the United States. It hasbeen effective in corn and soybean whencombined with a band of herbicide applied

over the crop row. Swanson and Jacobson

and Johnson reported non-weed controlbenefits of inter-row cultivation such asimproved soil aeration and reduced soilcompaction. However, most benefits of inter-row cultivation are attributable to weed

control. Research on inter-row cultivation offield crops in Saskatchewan is very limited.Inter-row cultivation in cereal crops wasinvestigated at the University of Saskatchewan

in the 1920’s. The purpose of that researchwas primarily to reduce summerfallow andmanage drought, and not to manage weeds.Two to three rows of wheat, oat, or barley(spaced 15 cm apart) were separated by a 90cm spacing to facilitate cultivation. Barley andoats appeared to respond best to the treatment;however, there were no non-cultivated checksfor comparison. Subsequent wheat cropsyielded similar to wheat crops grown onfallow. These results were similar to the

observations of Tull, who stated that “the moresuccessive crops are planted in wide intervalsand often hoed, the better the ground doesmaintain them”.

The study was conducted on cereal stubble atthe Scott Research Farm in 1998 and 1999.Wild oat and wild mustard were seeded on theexperimental area in early spring followed by acultivation to distribute weed seeds. Field peawas seeded at a depth of 7.5 cm on May 12,1998 and May 7, 1999. We used a hoe-drillplot seeder with adjustable row spacing andon-row packing. The crop was seeded insingle rows spaced 33 cm apart to facilitate

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9-6 Inter-row cultivation – effective weed control in field pea?

– E. Johnson, B. Frick - Scott Research Farm


134

References1

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3

4

5

6

7

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Hanna, M., R. Hartzler, D. Erbach, K. Paarlberg, and L. Miller. 1996. Cultivation: An effectiveweed management tool. Iowa State University Extension Publication PM-1623. Iowa StateUniversity. Ames, Iowa.

Krausz, R.F., G. Kapuista, and J.L. Matthews. 1995. Evaluation of bands vs. broadcastherbicide applications in corn and soybeans. J. Prod. Agric. 8: 380-384.

Swanson, C.L.W. and H.G.M. Jacobson. 1953. Herbicides: a new tool for use in studying soilphysical properties affecting crop growth. Weeds 1: 174-184.

Johnson, R.R. 1986. A new look at cultivation. Crops Soils 37: 13-16.

Gonsolus, J.L. 1990. Mechanical and cultural weed control in corn and soybeans. Am. J. Alt.Agr. 5: 114-119.

Champlin, M. 1933. Growing grain in cultivated rows. College of Agriculture FieldHusbandry Circular 505. University of Saskatchewan. Saskatoon, SK.

Champlin, M. 1933. Experiments with inter-tilled crops. College of Agriculture FieldHusbandry Circular 505A. University of Saskatchewan. Saskatoon, SK.

Tull, J. 1762. Horse-hoeing husbandry: or, an essay on the principles of vegetation andmanagement. A. Millar. London.

Holt, J.S. 1987. Ecological and physiological characteristics of weeds. p. 7-24. M.A.Altieri and M. Liebman, (ed.) Weed Management in Agroecosystems: Ecological ApproachesCRC Press Inc., Boca Raton.

Vangessel, M.J., E.E. Schweizer, R.G. Wilson, L.J. Wiles, and P. Westra. 1998. Impact oftiming and frequency of in-row weed control in dry bean ( ). Weed Technol.12: 548-553.

Buhler, D.D., J.L. Gonsolus, and D.F. Ralston. 1992. Integrated weed managementtechinques to reduce herbicide inputs in soybean. Agron. J. 84: 973-978.

In.

Phaseoulus vulgaris

Funding

Further information –




Table 1. Effect of inter-row cultivation on wild mustard density infield pea. Mean of two years (1998-99). Scott, SK.

Treatment

No inter-row cultivation1 inter-row cultivation (6-node stage)2 inter-row cultivations (6 + 8 node stages)3 inter-row cultivations (6, 8 + 10 node stages)Herbicide treatmentLSD0. 05

Wild mustard density(plants/m )

2

1557956603065

Table 2. Effect of inter-row cultivation on field pea yiels (kg/ha).

Treatment

No inter-row cultivation1 inter-row cultivation (6-node stage)2 inter-row cultivations (6 + 8 node stages)3 inter-row cultivations (6, 8 + 10 node stages)Herbicide treatmentLSD0. 05

Field pea yield (bu/ac)1998

15.818.219.321.224.83.1

1999

14.920.326.524.447.06.6

135

9-7 Post-emergence harrowing for weed control

– E. Johnson - Scott Research Farm

Problem

Background

Organic crop production practices such as croprotation, use of clean seed, careful use oftillage between crops, and good crophusbandry reduce problems with weeds.However, some weeds are likely to be found inthe crop, and can cause yield loss if allowed tocompete with the crop throughout the growingseason. Can post-emergence harrowing beused to reduce these problems?

Harrowing after seeding but before the cropemerges can be useful if weeds emerge beforethe crop. A rod weeder, cable weeder orflexible harrow may be used. Tillage with adrag or flex harrow after the crop emerges canalso be effective. A rotary harrow can be usedwith an excess of trash, where a tine harrowwould clog. Pre-seeding harrowing needs anaggressive angle, but post-emergenceharrowing should disturb plants as little aspossible. Harrowing may not kill all theweeds, but can damage them, to allow the cropa competitive advantage. Extra caution is

needed if conditions are very dry. Weeds suchas Russian thistle, tumble mustard, wildbuckwheat, stinkweed, green foxtail, lambsquarters and redroot pigweed can be controlled

well. Control of wild oat with post-emergent

harrowing can be quite variable. Kirklandreported that multiple post-emergenceharrowing passes reduced wild oat panicles andfresh weight in spring wheat in two years outof a three-year study. However, spring wheatyield was improved in only one year of thestudy. Three to four passes were required toreduce wild oat fresh weight by 40 to 80%.

Crops are generally harrowed with the rows.Limited research done in western Canada andEurope indicates that harrow direction has littleeffect on selectivity (ratio of weed control tocrop injury). Tables 1 and 2 discuss factors andtimings for best results when harrowing post-emergence for weed control.

1

2 ,3

4

Table 1. Factors affecting the efficacy ofpost-emergence harrowing

-- Harrow less than 2 inches deep -- Large amounts of trash-- Soil is dry -- Compacted soil-- Crop seeded heavy, deep -- Weed seeds deep in soil-- Cool wet conditions following -- Poor growing conditions

harrowing to let crop recover following harrowing

Factors improving success Factors reducing success

Table 2. Optimum timings for post-emergenceharrowing for weed control

Wheat 2 - 4 leafBarley 2 - 4 leaf, before tilleringOat not recommendedSunflower up to 6 leafFababean 2 - 6 inches tallLentil seedling less than 4" tallField pea seedling less than 4" tallCanola not recommendedFlax not recommended

Recommended crop stages for harrowing

Crop Stage for harrowing

Study description

Major findings

Studies were conducted in 1998 and1999. Wild mustard and wild oatswere seeded as weeds. Theexperiment included field pea,canola, flax, lentil, and chickpea.Crops were harrowed at a combin-ation of stages including emergence,three-, five- and seven-leaf stage. Acheck plot received no harrowingtreatment. Harrowing was with atine harrow, and was either a singleor double pass at each timing. Theexperimental design was a split-plotwith four replicates.

Weed control in the study waserratic, however the study was veryuseful in determining the relativetolerance of crops to post-emergence harrowing. Crop injurywas assessed by counting thenumber of crop plants remainingafter the harrowing treatment. Fieldpea was very tolerant with 85 to90% of the plants remaining afterharrowing (Figure 1). Chickpeawas also very tolerant; however,producers should be cautious withthis practice since physical injurycould make chickpea moresusceptible to Ascochyta blight.Lentil showed intermediatetolerance to post-emergenceharrowing, while canola and flaxdid not tolerate harrowing.

ConclusionsPost-emergence harrowingfor weed control can berecommended in field pea.Harrowing should beapproached cautiously forlentil and chickpea untilmore is known about theimpact of harrowing ondisease spread. Post-emergence harrowing is notrecommended in eithercanola or flax.


136

References1

2

3

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5

Smith, G., 1995. The harrow and hoe: Post emergence weed control inSouthwest Saskatchewan. Synergy Winter 1995:19-22.

Foster, K., 1996. FARMFACTS. Organic Crop Production: WeedManagement. Sustainable Production Branch, Saskatchewan Agriculture andFood.

Report of the Superintendent for the year 1924. Experimental Station, SwiftCurrent, Sask. Dominion of Canada, Department of Agriculture, DominionExperimental Farms.

Kirkland, K.J. 1994. Frequency of post-emergence harrowing effects wildoat controland spring wheat yield. Can. J. Plant Sci. 75: 163-165.

Saskatchewan Pulse Crop Development Board. 1995. Pulse ProductionManual. Saskatchewan Agriculture and Food.

Funding

Further information



Figure 1. Percent reduction in plant stand due to post-emergence harrowing --mean of six harrow treatments -- Scott, 1998 - 1999.

100 --

80 --

60 --

40 --

20 --

0 -

%re

duct

ion

incr

opst

and

Field pea Chickpea Lentil Canola Flax

1998 1999


137

Post-emergence harrowinghad significant effects onfield pea density in bothyears. In both years, the tineharrow’s high disturbancesetting reduced field peadensity more than its lowdisturbance setting and bothrotary harrow settings (Table1). The tine harrow’s highdisturbance setting resulted ina 25% (1998) and 35%(1999) decline in field peadensity. The tine harrow’slow disturbance settingresulted in fewer problemswith crop residue pluggingthan did the high disturbancesetting. Residue attached tothe bottom of the tines on thehigh disturbance settingcaused more plant uprooting.The rotary harrow is designedto distribute crop residue andthis may account for its lackof crop injury.

In both years, harrow typehad a significant effect onwild mustard density (Table2). The tine harrow wasmore effective in reducingwild mustard density in bothyears. Harrow type had noeffect on wild oat density in1998; however, in 1999 thetine harrow’s high disturb-ance setting resulted in higherwild oat density and biomass,due to greater crop injury(Table 3). Increased plantcovering effects from the tineharrow’s high disturbancesetting was more effective incontrolling wild mustarddensity but this was offset byhigher crop injury.

Study description

Major findings

The experiment was conducted onspring wheat stubble in 1998 and1999 at the Scott Research Farm.Weeds were seeded in the earlyspring followed by a shallowcultivation to distribute weed seedsand crop residue. Field peas (Grande) were seeded on May 13,1998 and May 5, 1999. We used ahoe-opener plot seeder (22 cm rowspace) equipped with on-rowpacking. The experimental designwas a randomized complete blockand the treatment design was a2x2x2 factorial. Factors includedharrow type (rotary, tine), setting(low and high soil disturbance) andnumber of passes (single, double).Low and high soil disturbancesettings are illustrated in Figure 1.Our experiment included twochecks -- one untreated, oneherbicide treated.

Harrow treatments were carried outat field pea’s four - five node stage.The single pass harrowing operationwas done in the same direction asthe crop rows. In the double passtreatment, the second harrow passwas done in the opposite directionto the first. Harrowing speed was 6

km/hr . Plot size was 4x5 metersand each treatment was replicatedfour times. Crop burial was visuallyestimated on a scale of 0-100 percent immediately after harrowingwas done. We collected data oncrop and weed density and biomass,and crop yield.

The tine harrow buried more cropthan the rotary harrow in both years,particularly when harrows were setat high soil disturbance level. Therotary harrow’s high disturbancesetting and the tine harrow’s lowdisturbance setting (tines set at anangle of 45° backwards) buriedsimilar amounts of crop.

cv.

-1

Problem

Background

Post-emergence harrowing generally results inlow selectivity, which is the ratio between

weed control and crop injury. Many organicgrowers have suggested that post-emergenceharrowing’s selectivity could be improved withchanges in implement design. This study’sobjective was to determine if selectivitydiffered between a Phoenix rotary harrow and atine harrow.

The rotary harrow is manufactured in westernCanada and is designed for granular herbicideincorporation and field leveling under highcrop residues. The amount of soil disturbancecaused by the rotary harrow is dependent onthe angle of the harrow gangs in relation to thedirection of travel. Soil disturbance is lowwhen the harrow gangs are set perpendicular tothe harrow hitch and increases as the angleapproaches parallel.

Organic growers commonly use post-emergence harrowing for weed control;however it is not a practice commonly used byconventional growers. Fifty-two percent oforganic growers surveyed in Saskatchewanused post-emergence harrowing as a weed

control practice.

There are very few published papers on post-emergence harrowing in western Canada. Theresults of a 12-year study at Indian Headshowed that the yield of barley and springwheat grown under weed-free conditions wasnot reduced by a single harrow pass conducted

at emergence, the 1.5 or 2.5 leaf stage.

Kirkland reported that multiple post-emergence harrowing passes reduced wild oatpanicles and fresh weight in spring wheat intwo years out of a three-year study. However,spring wheat yield was improved in only oneyear of the study. Three to four passes wererequired in order to obtain a reduction in wildoat fresh weight of 40 to 80%.

Studies have shown that field pea can toleratepost-emergence tillage performed with a

harrow or rotary hoe. Yield responses frompost-emergence tillage in field pea have ranged

from 0 to 18%.

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9-8 Post-emergence field pea harrowing – rotary or tine?



138

This agrees with

findings – that a flexiblechain harrow was a moreefficient weed killer than aspring-tine harrow but it alsocaused more crop damage infield pea and spring wheat.He concluded that similarresults could be obtained withall harrow types, if theirsettings are adjusted to givesimilar plant covering effects.

In 1998, there was nosignificant increase in cropyield due to post-emergenceharrowing. In 1999, thehighest yields were obtainedwith the tine harrow's lowdisturbance setting and therotary harrow's highdisturbance setting (Table 3).The rotary harrow's lowdisturbance setting did notimprove crop yield since itdidn't effectively controlbroadleaf weeds.

Selectivity did not vary withharrow type. There wasopportunity to improveselectivity within bothharrow types by adjusting thelevel of soil disturbance andcrop burial caused by theharrow. A high level of soildisturbance and crop burialwas counter-productive assignificant crop injury offsetany improvements in weedcontrol. Since the tineharrow’s low disturbancesetting resulted in lower cropinjury without sacrificingweed control, producerswould be advised to set theirharrow tines at a 45° anglebackwards. On the rotaryharrow, a 45° angle providedboth satisfactory weedcontrol and crop tolerance.

Rasmuusen’s8

Conclusions

Figure 1. Soil disturbance settings for tine androtary harrows.

Tine harrow settings

High Low

Direction of travel

10°

45°

Rotary harrow settings

Low

Harrow

Harrow

Direction

oftr

avel

15°

15°

High

45°

45°


Table 1. Effect of harrow type and disturbancesetting on field pea density. --Scott, SK -- 1998 - 1999.

Harrow/setting

Tine / lowTine / highRotary / lowRotary / highUntreatedLSD0. 05

Field pea density (plants/m )1998

2

62526560667

1999

665064737410

Table 3. Effect of harrow type and disturbancesetting on wild oat biomass and fieldpea yield -- Scott, SK -- 1999.

Harrow/setting

Tine / lowTine / highRotary / lowRotary / highUntreatedLSD0. 05

1999Wild oat

biomass (g/m )2

247506216234223204

Field peayield (bu/ac)

35.227.228.432.426.1

5

Table 2. Effect of harrow type on wild mustarddensity -- means of two disturbance settins foreach harrow type -- Scott, SK -- 1998 - 1999.

Harrow

TineRotaryUntreatedLSD0. 05

Wild mustard density (plants/m )1998

2

25454214

1999

4611923525

References1

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3

4

5

6

7

8

Rasmussen. J. 1990. Selectivity, an important parameter on establishing the optimumharrowing technique for weed control in cereals. Proceeding of the 1990 European WeedResearch Society Symposium, Integrated weed management in cereals. Helsinki, Finland.Pages 197-204.

Beckie, M.A.N. 2000. Zero-tillage and organic farming in Saskatchewan: An interdicisiplinarystudy of the development of sustainable agriculture. PhD Thesis. University of Saskatchewan,Saskatoon, SK

Lafond, G.P. and K.H. Kattler. 1992. The tolerance of spring wheat and barley to post-emergence harrowing. Can. J. Plant Sci. 72: 1331-1336.

Kirkland, K.J. 1994. Frequency of post-emergence harrowing effects wild oat control andspring wheat yield. Can. J. Plant Sci. 75: 163-165.

Al-Khatib, K., C. Libbey, and R. Boydston. 1997. Weed suppression with greenmanure crops in green pea. Weed Sci. 45: 439-445.

Boerboom, C.M. and F.L. Young. 1995. Effect of postplant tillage and crop density onbroadleaf weed control in dry pea ( ) and lentil ( ). Weed Technol.9:99-106.

Rasmussen, J. 1993. Yield response models for mechanical weed control by harrowing at earlygrowth stages in peas ( L.). Weed Res. 33. 231-240.

Rasmussen, J. 1992. Testing harrows for mechanical control of annual weeds in agriculturalcrops. Weed Res. 32: 267-274.

In

Brassica

Pisum sativum Lens culinaris

Pisum sativum

Funding

Further information



139


References1

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Hoveland, C.S., G. A. Buchanan and M.C. Harris.1976. Response of weeds to soil phosphorous andpotassium. Weed Science 24: 194-201

Schipstra, K. 1957. Weeds as indicators ofnutritional diseases. Tjdschr. Piziekt. 63: 15-18.

Tilman, E.A., D. Tilman, M. Crawley and A.E.Johnston. 1999. Biological weed control via nutrientcompetition: potassium limitation of dandelions.Ecological Applications 9: 103-111

Peterson, L.A. A Field Guide to Edible Wild Plants.Eastern and central North America. Houghton MifflinCompany. Boston.

Marshall, T. 1992. Weed control in organic farmingsystems. Proceedings of the 1st International weedcontrol congress. Weed Science Society of Victoria,Melbourne, Australia. Vo. 2. pp 311-314



Funding

Further information

Some weeds are highly nutritious,as human food, or animal feed.They can be harvested, cut for feed,grazed, or left for wildlife. Lamb’squarters, dandelion, commonchickweed, and redroot pigweed canbe used in salad or as cookedgreens. Stinkweed seeds addflavour to salad dressings.Dandelion roots can be used as a

coffee substitute. Wild oats, kochiaand quack grass make nutritiousforage if cut early. Weeds thatemerge late in the season may causelittle crop loss in that year. If thefield is fenced, they might providesuitable grazing after harvest.

Weeds can harbour beneficialinsects, , birds, etc.Weed seeds at soil surface may bean important food source for insects.Weeds with a shallow nectar sourceare particularly important as foodsources for predatory wasps,hoverflies and other desirable

predatory insects.

4

5

mychorrizae

Even in a crop, weeds are not always aproblem. Volunteer pea in a wheat field maybe of more value than the wheat crop if it canbe separated after harvest. A few weeds in abean or pea field may reduce wind damage andhelp raise the pods higher off the ground,making them easier to harvest. In a wet year,weeds in a lentil field might stress the crop intoflowering, rather than producing onlyvegetative matter.

Weeds are signs of life in otherwise inhospit-able habitats. They play a role in both naturaland managed ecosystems. They alter the

environment

Conclusions

in ways that can be beneficial.

Weeds may indicate soil ormanagement conditions. Redrootpigweed and wild mustard, forinstance, do well only whenphosphorous levels are relatively

high, and thus they indicateadequate phosphorous when theyare abundant. Lamb’s quarters, onthe other hand, is more common in

phosphorous deficient soils, andthus may indicate a problem.Dandelions do poorly in soils low in

potassium. Other weeds, such asfoxtail barley, may indicate saltaccumulations. Thus weeds cansignal the astute manager thatmanagement changes are required.

1

2

3

Problem

Background

Weeds are often defined asplants growing where theyare unwanted. The definitionreflects our attitude, butdoesn't help us understandthe roles these plants play inmanaged ecosystems.

In natural environments,weeds are the first species tocolonize disturbed habitats.Many weeds are well adaptedto survive and reproducewhere other plants can not –often in conditions of lowfertility or frequentdisturbance. Weeds canmodify these habitats in waysthat make them morehospitable for other species.Weeds shade the soil surface– reducing evaporation andthe sun’s harmful effects.They can reduce wind speedsat the soil surface. In winter,they trap snow, adding to soilmoisture. Weeds can beimportant agents of soilconservation. Weed roots canstabilize erodible soil andprovide channels for themovement of water and air inthe soil. They contribute tosoil tilth.

Some weed roots penetrate sodeeply that they tap nutrientsunavailable to crop plants.The weeds bring thesenutrients to the surface as theplant grows new shoots orshallow roots. When weedsdie and decompose, thosenutrients become available inthe soil's surface layers.Weeds can also add substan-tial organic matter to the soil.

9-9 Weeds -- when are they a good thing?


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141

Helpful insects can beencouraged by providinghabitat, such as shelterbeltsand ground cover. Increasedweed seed predation has beenobserved with cover crops.

Reader reported that ground-cover restricted seedlingemergence by providing ahabitat for seed predators.High numbers of insects,snails, slugs, and voles werereported in heavy residues ofrye and hairy vetch and it wasfelt that these organisms’feeding decreased the number

of weed seedlings. Somecarabid insects show a prefer-

ence for species of foxtail.

Livestock can be useful inweed management both asdirect consumers of weeds,and because livestock providecost recovery for some weedmanagement practices suchas chaff collection ormowing. Other beneficialorganisms can be encouragedby leaving naturalenvironments within the farmecosystem, by reducingtillage, and by usingchemicals judiciously.

9

1 0

9

Conclusions

Beneficial creatures other thanlivestock may also be important inweed management. They can beencouraged by maintaining habitatfor them. This might includereducing tillage, maintainingshelterbelts and wooded refuges,sloughs, or borders, and leavingunbroken native land. Blind use ofrefuge habitats is risky, because it isdifficult to determine, at first, ifcreatures harbored this way arebeneficial or harmful. However,careful observation should helpmake that decision. Our usual habitof viewing all non-domesticatedcreatures as pests may be cautious,but it is unwarranted.

Biological agents in the soil can alsoaffect competitive relationshipsamong crops and weeds. Somebiological agents are available toimprove crop growth, such as therhizobial inoculants used withlegumes to support nodulation orthe fungal organism of

to solubilize inorganicphosphorus in the soil. Arbuscularmycorrhizae (AM) can benefitplants by facilitating nutrient uptake

and improve growth and yield.These mycorrhizae benefit somespecies such as cereals and legumesover species that do not associate

with them, such as wild mustard,lamb’s quarters, wild buckwheat,tame mustard, canola and quinoa.

Other soil organisms can be directlydetrimental to weeds. Seed-bornebacteria may effectively reducedormant weed seed populations.Rhizobacteria have potential toreduce the vigor of grass weeds incereal crops. Applying microbialagents to control weeds may proveuseful in the future. Reducingtillage might foster growth of thesebacteria, which actively grow oncrop residues, and are favored bythe cooler, moister environment the

residues generate.

Penicllium

billai

7

7

8

Problem

Background

Many plants considered weeds in agriculturalcrops are actually highly nutritious andpalatable plants. Can livestock use weeds? Canwe integrate livestock and other weed eatinganimals into a weed control strategy?

On mixed farms, livestock may be useddirectly to graze weeds, or consume mownweeds, chaff, and screenings. Goats arebrowsers, and are especially good at controllingwoody plants, such as aspen or rose. Goats

also eat thistles. Sheep can effectively controlleafy spurge. Once they acquire a taste for it,sheep consume large quantities of spurge,

which gives them nutritious forage. Sheep areespecially good for weed control, as they grazeclose to the ground, and will readily eat

thistles. In legume crops, sheep will graze out

grassy weeds. Geese have been used in garden

plots to control grassy weeds. Weeder geesecan be used (at five to six geese/hectare) aftercrops grow too large for birds to eat. Hogs, at24 animals/hectare, can control perennialweeds between cropping seasons in fencedfields. Cattle and sheep can be used for earlygrazing to prevent weed growth. Weedregrowth faces strong competition from

legumes and grasses in pasture. If livestockare used to graze mature weeds, or to disposeof screenings or chaff, digestion will destroy

many, but not all, weed seeds.

Livestock also have indirect benefits in a weedmanagement system. Livestock reclaimotherwise-useless things like screenings, chaff,patches mown for weed control, and thesepractices become more viable for the producer.

Long-term rotations that include a perennialoffer distinct benefits to soil quality and weedmanagement. Currently, the usual way to getalfalfa or another perennial legume back intothe rotation is to include livestock as part of the

production system. Options that generate the‘livestock advantage’ without livestock mightalso be pursued. For instance, dehy and seedalfalfa producers might develop partnershipswith livestock producers.

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9-10 Livestock and other beneficial organisms for weed management



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References1

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8

9

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Loiselle, M. personal communication

Anonymous. 1994. Practical Crop Protection. Weeds, Insects, Diseases.Alberta Agriculture Food and Rural Development Publishing Branch.

Marshall, T., 1992. Weed control in organic farming systems. Proceedings ofthe 1st International weed control congress. Weed Science Society of Victoria,Melbourne, Australia Vol 2: 311-314

Liebman, M., 1988. Organic and low herbicide approaches for weedmanagement. Proc. Bioregional Farmer/Scientist Workshop in OrganicAgricultue (Maine &Maritime Provinces 1988). D. Patriquin, ed. Fredricton, NewBrunswick

Wyse, D.L. 1994. New technologies and approaches for weed management insustainable agriculture systems. Weed Technology 8: 403-407.

Reganold, J.P., R.I Papendick and J.F. Parr. 1990. Sustainable agriculture.Scientific American. June 1990: 112-120.

Boyetchko, S. M. 1996. Impact of soil microorganisms on weed biology andecology. Phytoprotection 77: 41-56.

Derksen, D.A., R.E. Blackshaw and S.M. Boyetchko. 1996. Sustainability,conservation tillage and weeds in Canada. Can J. Plant Sci. 76: 651-659.

Reader, R.J. 1991. Control of seedling emergence by ground cover: a potentialmechanism involving seed predation. Can. J. Bot. 69: 2084-2087

Mohler, C.L. and J.R. Teasdale. 1993. Response of weed emergence to rate ofRoth and L. residue. Weed Res. 33: 487-499.

Lund, R.D. and F.T. Turpin. 1977. Carabid damage to weed seeds found inIndiana corn fields. Environm. Entomol. 6: 698-698.

Vicia villosa Secale cereale

Funding

Further information




In experimental comparisons oforganic and conventional systems inSouth Dakota, annual broad-leavedweeds were not consistentlydifferent in organic systems than inconventional systems. Grassy weednumbers, mostly green and yellowfoxtail, were substantially higherafter six years in organic cerealsthan they were in conventionalcereals. They were not consistently

higher in organic soybeans.6

ConclusionsWeed communities varybecause of many factors.Factors such as croppingsystem, year and region canbe more important thanwhether farms are managedorganically or not. Organicfarms will likely have morewild mustard, lamb’squarters, Canada thistle,bluebur and redroot pigweedthan will conventional farms.

Problem

Background

Are the weeds on organic farms different fromthose on neighboring farms?

Weeds, like all plants, live in the context oftheir environment, the history of the land andthe random workings of chance. Some of themost important factors that make up theenvironment are beyond a farmer’s control,such as climate. Some factors important toweed development, like soil temperature andmoisture, reflect both the local climate andspecific farm management. Farm managementon organic farms is often different fromneighboring farms, and thus weed communitiesmight be expected to be different.

One study in Saskatchewan indicated thatorganic systems had more weed species andmore individual weed plants than conventionalsystems. Wild mustard, lamb’s quarters andCanada thistle especially were more abundantin organic systems. Wild oats were relativelyless of a problem. In that study, differencesamong years were greater than differences

between organic and conventional systems.

A second study compared larger numbers ofSaskatchewan organic and non-organic farms.It concluded that cropping system, especially ifthe farm had a history of perennial foragecrops, had a greater influence on the weedcommunity than whether the farm wasmanaged organically or not. Perennial foragestended to encourage perennial and biennialweeds, while annual cropping systemsencouraged annual weeds. Organic fields hadgreater numbers of weed species mostsusceptible to herbicides -- wild mustard,

lamb’s quarters and bluebur (Table 1).Organic fields had more individual weeds, onaverage, and greater numbers of weed species

than neighboring fields.

In a Manitoba study, organic producersreported problems with wild mustard, Canadathistle, red root pigweed, green foxtail and wildoats. Wild mustard was much more of aproblem for organic producers than their

conventional counterparts (Table 2).

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9-11 Weeds on organic farms


143


Table 1. Comparison of weed density (#/m ) in different cropping systems* and in organicsystems relative to those with moderate levels of chemical inputs (Mod).

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Head

StinkweedGreen foxtailWild buckwheatLamb's-quartersWild oatsNarrow-leaved hawk's-beardQuack grassRussian thistleShepherd's purseCanada thistleWild mustardDandelionPerennial sow-thistleField horsetailVolunteer canolaVolunteer wheatKochiaFlixweedBlueburCleavers

* Fallow systems include fallow; annual and perennial cropping systems includ perennial crops;annual cropping systems do neither of the above.

Organic

44.145.36.175.719.30.90.94.31.11.552.31.30.80.50.70.33.00.81.5

< 0.1

FallowMod

16.217.41.70.60.90.61.02.6

< 0.1< 0.1

< 0.1< 0.1

0.90.21.60.7

< 0.1

Organic

40.385.39.352.84.61.60.78.55.41.46.30.20.62.80.20.50.10.21.8

< 0.1

Annual cropsMod

13.410.14.71.09.52.91.31.34.31.60.50.20.70.32.31.0

< 0.1< 0.1< 0.12.1

Organic

21.230.424.124.70.7

24.931.51.2

18.71.50.14.62.03.0

0.11.11.3

Annual andperennial crops

Mod

11.91.95.04.40.334.523.31.10.80.3

< 0.116.11.11.1

< 0.1< 0.122.46.80.4

144

Table 2. Comparison of weed problems reported by Manitoba organic producers and weednumbers found on Manitoba farms (mostly not farmed organically)

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References1

Frick, B. 1993. Weed communities in organic and conventional wheat fields.Proceedings of the Soils and Crops Workshop. University of Saskatchewan,Saskatoon. 164-169.

Leeson, J. Y., Sheard, J. W., and Thomas, A. G. 1998. Weed communitiesassociated with arable Saskatchewan farm management systems. Can. J. PlantSci. 00:000-000.

Leeson, J.Y., A.G. Thomas and J.W. Sheard. 1999. Weed diversity inSaskatchewan farm management systems. Proceedings of the Fifth PrairieConservation and Endangered Species Conference, Saskatoon, Saskatchewan.Natural History Occasional Paper No. 24. J. Thorpe, T. A. Steeves and M. Gollopeds. Provincial Museum of Alberta, Edmonton AB. 288 to 292.

Entz, M.H, R. Guilford and R. Gulden. Productivity of organic cropping in theeastern prairies: on-farm survey and database development.

Thomas, A.G., B.L. Frick, R.C. Van Acker, S.Z. Knezevic and D. Joosse. 1997.Manitoba weed survey of cereal and oilseed crops in 1997. Weed Survey SeriesPublication 98-1. Agriculture and Agri-Food Canada, Saskatoon, SK

Smolik, J.D., Dobbs, T.L., D.H. Rickerl, L.J. Wrage, G.W. Buchenaw, and T.A.Machacek. 1993. Agronomic, economic and ecological relationships inalternative (organic), conventional, and reduced-till farming systems. SouthDakota Agricultural Experimental Station bulletin. 57 pp.

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Further information




Weed species

Wild mustardCanada thistleRedroot pigweed

Green foxtailWild oatsWild buckwheat

Quack grassPerennial sow thistleLamb's-quartersCurled dock

* Importance is equal to the number of reports for a given species, expressed as a percentageof all species reports (i.e. larger numbers indicate greater importance)

Organic producersRelative importance*

211814

13125

4432

Other producersRelative importance*

464

28119

3330

145

Weeds that remain green atharvest, especially those withfibrous stems, can interferewith harvest. The problemvaries with both the crop andthe weed. A low-growingweed like wild tomato causesvery little problem in a cerealcrop because most of theplants are below swathheight. In a crop like lentil,chickpea, or bean, severeharvest difficulties mayoccur. The low cut meansthat wild tomatoes areharvested with the crop, andthey can stain the pulse and

clog the machinery. Weedslike wild buckwheat, thattwine through a crop can alsobe problematic.

Weeds can harbour probleminsects and crop diseases.For instance, mustard-familyweeds can carry over canoladiseases, making rotation aless effective tool for diseasemanagement.

Immature weeds can interferewith harvesting operations.Weed seeds in harvestedcrops cause dockage andincrease risk of spoilage.This can reduce crop value,or increase shipping costs.

7

Relative timing of crop and weedemergence is very important indetermining the magnitude of yieldloss from weed competition. Whenit comes to plant competition,generally the first one out of theground wins. Competition fromwild oat resulted in a 17% yield lossin barley when it emerged five daysbefore the crop compared to a 3%yield loss when wild oat emerged

five days after crop emergence.

Weed size is partly a matter oftiming. Weeds that emerge beforethe crop are generally larger andbetter established than those thatemerge after the crop. This givesthem greater access to soil andspatial resources, and thus they domore damage to crop yield. Sizealso varies among species. Forinstance, three Canada thistle plantsare naturally much larger, and likelyto cause more yield loss, than threethyme-leaved spurge plants. Sizealso depends on plant nutrition,disease, and pests.

Some weeds may limit cropdevelopment through chemicalmeans, or allelopathy, either whilethey are alive, or as theydecompose. Some weeds, forexample Canada thistle or quackgrass, release chemicals that inhibittheir neighbors. This affects theircompetitive relationships.

Weeds can cause problems otherthan crop yield loss. Some weedsare poisonous and can taint food andfeed crops. For example, wildmustard seed cannot readily beremoved from canola, and canflavor the resulting canola oil ifcrushed with the crop seed.Stinkweed in feed for dairy cattleproduces off-flavors in milk.

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Problem

Background

Weeds are often defined as plants growingwhere they are unwanted. What makes theseplants so undesirable? What sort of problemscan weeds cause?

Farmers are often concerned that weeds mayreduce crop yields. Weeds use the samenutrients that crop plants use, often in verysimilar proportions. They also use resourcessuch as water, sunshine and space that mighthave gone to crops. The more similar the weedand crop requirements, the more they willcompete for those resources. Weeds thatcompete aggressively with crops reduce theiryield. Weeds are most damaging to crop yieldsif they have some advantage over the crop.Four factors are especially important: density,timing, size and chemistry.

More weeds are generally a larger problemthan few weeds, but weed density is not the

only concern. For instance, at very highdensities, green foxtail plants tend to competestrongly with each other and thus remain verysmall. These small plants probably have littlecompetitive effect on the crop even when thereare many of them. At medium densities, greenfoxtail plants grow larger and can severelyreduce crop yields. In this example, areduction in weed numbers may actuallyincrease the weed problem.

Timing of weed-crop competition is important.Ecologists have defined a critical period ofweed competition. This is the time when theweed reduces crop yield. Weeds that areremoved before the critical period, or thatemerge after the critical period do not causeany appreciable yield loss. The exact timing ofthis period is not an “inherent property of the

crop” and varies for different crops, fordifferent weed species, and under different

conditions such as year or location. Ingeneral, weeds should be removed at early cropgrowth stages. Early weed removal was found

necessary to protect field pea yield.

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9-12 Weeds - when are they a problem?



ConclusionsWeeds cause many problems.Most importantly, weeds canreduce crop yield. Weedscause greater crop losses ifthey occur in large numbers,if they get a head start on thecrop, if they are especiallyvigorous, or if they produceallelopathic substances.Other problems weeds causeinclude dockage, taintedproducts such as feed or food,increased numbers of harmfulinsects or diseases, and moredifficult harvest.

References1

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Stopes, C. and S. Millington. 1991. Weed control in organic farming systems. Proceedings ofthe Brighton Crop Protection Conference, Weeds. Vol 1: 185-192

Medd, R.W. 1987. Weed management on arable lands. Ch 9 P.S. Cornish and J.E. Pratley,eds. Tillage: New directions in Australian Agriculture. Indata Press, Melbourne.

Zimdahl, R.L. 1988. The concept and application of the critical weed-free period. M.A.Altieri and M. Liebman, eds. Weed Management in Agroecosystems: Ecological Approaches.Boca Raton, Fla: CRC Press. Pp. 145-155.

Weaver, S.E. 1984. Critical period of weed competition in three vegetable crops in relation tomanagement practices. Weed Res. 24: 317-325.

Harker, K.N., R.E. Blackshaw, and G. Clayton. 2001. Timing weed removal in field pea( ). Weed Tech. 15: 277-283.

O’Donovan, J.T., E.A. de St. Remy, P.A. O’Sullivan, D.A. Dew, and A.K. Sharma. 1985.Influence of the relative time of emergence of wild oat ( ) on yield loss of barley( ) and wheat ( ). Weed Sci. 33: 498-502.

Frick, B. and F.A. Holm. 1994. Wild tomato. Saskatchewan Pulse Crop Development BoardNewsletter 10: 7-8.

in

In

Pisum sativum

Avena fatuaHordeum vulgare Triticum aestivum

Funding – Canada-Saskatchewan Agri-FoodInnovation Fund


Further information

146

Weeds in grasslands aregenerally those that are lesspalatable. They increase withgrazing, because the livestockgraze them less than the morepalatable plants. Over time,this reduces range

productivity for livestock.Weeds such as smooth bromeor purple loosestrife cancompete aggressively withnative vegetation, and replaceit.

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9-13 Crop husbandry for weed management


In one Saskatchewan study,increasing peas' seeding ratereduced weed numbers; highpea populations competed

well with weeds. In anotherstudy at Scott, barley yieldedthe most at narrow rowspacing and increasedseeding rate. Weed biomasswas reduced by bothnarrower row spacing and

increased seeding rate.

Narrow row spacing allowscrops to fill the availablespace more completely,leaving less space for weeds.Cross-seeding is anotheralternative that needs nomachinery modification, buthas much the same effect.

Good crop husbandry is aneffective weed managementsystem. Two primaryprinciples of crop husbandryrelate to weed management:

vary farm practice to avoidhaving weeds adapt to itwhenever possible, give theadvantage to the crop, notthe weed.

Practices recommended forweed-free conditions mayneed to be altered for weedyconditions. High seedingrates, and close plantingpatterns leave lessopportunity for weeds.

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Conclusions

�

�

Seeding rates and patterns can alsohave an effect on how well a cropcompetes. High seeding rates andnarrow row spacing decrease thedistance between crop plants, andthe canopy closes sooner. Thisreduces weed seedling germination,and gives the crop an edge in earlycompetition. The disadvantages areincreased seed costs, and less-feasible inter-row cultivation.

High seeding rates are especiallyhelpful on weedy land. On weed-free land, high seeding rates offer noadvantages over recommended

seeding rates. Green feed andsilage crops can be seeded at higherrates to increase crop competitionand feed quality. Increased seedingrates should also be used if eitherpostseeding or postemergencetillage is planned. This will helpcompensate for any damage causedby in-crop tillage. An increase of25% above normal is oftenrecommended. High seeding ratesmay be advantageous in a dry yearif seedlings more effectively coverthe soil and reduce evaporation fromthe soil surface. If there is enoughmoisture, high seeding rates willspeed maturity (two to three days),and result in shorter plants withfewer tillers. Under certainenvironmental conditions, higherseeding rates may increase diseaseincidence or may result in higherlodging losses.

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Problem

Background

What is crop husbandry? How is it importantfor weed management?

One of the most effective weed management

tools is good crop husbandry. A strong andcompetitive crop offers less opportunity forweeds. All crop management techniques thatcontribute to good growth can be consideredweed management tools. Crops can competewell with weeds if they establish quickly and

uniformly, are vigorous, and well nourished.

Agronomic recommendations are oftenassembled from results obtained in virtuallyweed free experimental plots. A combinationof sowing time, crop genotype, crop plantingarrangement, crop density and fertilizer inputthat's optimal under weed free circumstances isnot necessarily optimal in weedy fields.Moreover, desirable husbandry practices cancontribute considerably to weed control at very

little extra cost.

Two primary principles of crop husbandryrelate to weed management:

vary farm practice to avoid having weedsadapt to itwhenever possible, give advantage to thecrop, not the weed.

Varying farm practice prevents weeds thatprosper in one system from gaining too strongan advantage. Many factors can be varied to‘confuse’ the weeds. These include:

extensive and varied crop rotationsalternating timing of operations such asseeding and harvestvarying tillage amount and timingmodifying soil fertility through greenmanures, livestock manures and other soilamendments, and using crops that depletenutrients to a greater or lesser extent.

Slight alterations of existing practices are oftenenough to change their relative advantage. Forinstance, on-row packing, rather than packingthe entire field may give an advantage to thecrop relative to most of the weeds. Bandingliquid manures near the crop row, rather thanacross rows may mean a relatively greatershare of them goes to the crop.

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References1

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Pavlychenko, T.K. 1942. The place of crested wheat grassL. in controlling perennial weeds. Sci Agr. 22: 459-460.

Hanley, P. 1980. Earthcare: Ecological Agriculture in Saskatchewan.Earthcare Group, Regina. Earthcare.

Medd, R.W. 1987. Weed management on aerable lands. Ch 9 P.S.Cornish and J.E. Pratley, eds. Tillage: New directions in AustralianAgriculture. Indata Press, Melbourne.

Godel, C.L. 1935. Relation between rate of seeding and yield of cerealcrops in competition with weeds. Sci. Agr. 16: 165-168.

Results of experiments 1931-1936 inclusive. 1938. Experimental sub-station, Regina, Saskatchewan, Dominion of Canada, Dept. Of Agriculture,Dominion Experimental Farms.

Townley-Smith, L. and A.T. Wright. 1994. Field pea cultivar and weedresponse to crop seed rate in western Canada. Can. J. Plant Sci.: 387-393.

Kirkland, K.J. 1993. Weed management in spring barley () in the absence of herbicides. Journal of Sustainable Agruiculture 3:

95-104

Agropyroncristatum

in

Hordeumvulgare

Funding

Further information




149

A Saskatchewan studyindicated that weedpopulations were affectedmore by frequency ofperennial forages in rotationthan by any other manage-ment factor studied. Whenforage crops' frequencywithin a rotation increased,there were more perennial orwinter annual weeds such asdandelion, smooth brome,quack grass and narrow-leaved hawks-beard -- andfewer annual species. Otherfactors influencing weedcommunities less thanrotation were the number oftillage passes and fallowfrequency. Both tillage andfallow encouraged annualweed growth, but discour-aged both perennials and

winter annuals.

A good crop rotation isdependent on the site, themanager, field history and therest of the farm operation, buta guideline for weedmanagement is to include asmuch diversity as you arecomfortable with. Croprotations can vary timing ofdisturbances (such as earlyseeded, late seeded, wintercrops, biennials, perennials,and green manures). Croprotations can account fordifferences in nutrientrequirements. For instance, athree year alfalfa crop mightbe followed by wheat (whichwill use nitrogen from alfalfabreakdown), a legume (thatwould not require a high

1 2

The greater the differences betweencrops in a rotational sequence, thebetter cultural control of pests can

be expected. In a Saskatchewanstudy, the presence of winter wheatin a rotation was the factor with thelargest impact on quackgrassgrowth. When winter wheatestablished well with adequate

moisture, it suppressed quackgrass.

Including alfalfa or other perenniallegumes in rotations may beespecially helpful in managing weed

problems. This solution is limited,in part, by the small number of

farms with livestock. Thisproblem might be overcome throughcreative marketing (to livestockproducers or the dehy industry), inthe use of alfalfa grown for seed,and of short-term plow-downs whenseed prices are favorable. A furtherconstraint results from perenniallegumes’ high moisture requirementresulting in severe soil drying. Forthis reason, introducing perenniallegumes should be done cautiously,with on-farm feasibility testing.

Using legumes in rotation began todecline when synthetic nitrogen was

introduced in the 1940's. Makingrotations shorter (not includingperennials, pastures, green manuresand increased summerfallow) hasreduced soil organic matter,degraded soil physical properties,and increased erosion and external

inputs. Once established, foragegrasses and legumes withinrotations are very effective insuppressing growth of some annualweeds. This is a consequence ofleaving the soil surface undisturbed,providing dense crop canopy coverand root development, and mowing.Mowing affects annual weed growthmuch more severely than it affects

forage grasses and legumes.

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Problem

Background

Crop rotations are considered the key to soundorganic farming practice. Why are croprotations important? What is a good organiccrop rotation?

Crop rotation is a planned sequence of differentcrop types, such as spring-seeded cereals, fall-seeded cereals, oilseeds, pulses, perenniallegumes and other perennial species. Rotationsalso include alternating crop types, for instancebetween barley and wheat, or flax and canola;or alternating cultivars within a crop species,for instance, between Harrington and Brierbarley.

Crop rotation is a central component of allsustainable farming systems. Crop rotationoffers the most effective, indirect method ofminimizing pest, disease and weed problemsand maintaining and enhancing soil structure

and fertility. Crop rotations can limit build-upof weeds that are favored in a single crop

environment. Crop rotations have manybenefits, including increased soil microbialactivity, which may increase nutrientavailability, including phosphorus. Whencrops are rotated, yields are usually 10 to 15%

higher than when grown in monoculture.

Each crop has unique characteristics, and thusrequires different kinds of disturbances, such asdifferent seeding times, different tolerance topractices such as post-emergence harrowing,etc. Crop rotation dictates the pattern of thesedisturbances, that ultimately change weed

species' composition within agroecosystems.Thus, in spring-sown crops there is selectionagainst autumn-germinating weed specieswhile the opposite is true of autumn-sown

crops. There has been evidence since at leastthe 1800s that weed incidence varies with crop

rotation. An extensive literature survey ofover 200 references indicated that weednumber, biomass and seed production arereduced in rotations and intercropping

situations compared to monoculture.

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9-14 Crop rotations for organic systems



150

nitrogen level and would fixatmospheric nitrogen moreeffectively at low soilnitrogen levels), wheat again,and then oats (with a small

nutrient requirement).Rotating crops for disease andinsect management cancontribute to a healthy cropwith less opportunity forweed growth. Crops can berotated according tocompetitive ability. Forinstance, competitive cropssuch as barley or alfalfa couldbe grown before lesscompetitive crops such as flaxor lentil to start the lesscompetitive crops in as cleana field as possible. Using acompetitive crop, or severalcompetitive crops following aless competitive crop may beused for clean up. Weedsuppressing cover crops suchas fall rye or sweet-clover canreplace some of thesummerfallow land.

A good crop rotation isimportant in reducing weeds,diseases, nutrient depletionand in improving crop vigour.An ideal rotation balancesrequirements of crops andsoil, disturbance timing andfarmer comfort.

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Conclusion

References1

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Jordan, V.W.L. 1992. Opportunities and constraints for integrated farming systems. Proc. 2nd

European Society of Agronomy congress, Warwick University.

Liebman, M. 1988. Organic and low herbicide approaches for weed management. Proc.Bioregional Farmer/Scientist Workshop in Organic Agriculture (Maine & Maritime Provinces1988). D. Patriquin, ed. Fredricton, New Brunswick

Reganold, J.P., R.I. Papendick and J.F. Parr. 1990. Sustainable agriculture. ScientificAmerican June 1990: 112-120.

Ball, D.A. and S.D. Miller. 1990. Weed seed population response to tillage and herbicide usein three irrigated cropping sequences. Weed Science 38: 511-517.

Froud-Williams, R.J., R.J. Chancellor and D.S.H. Drennan. 1981. Potential changes in weedflora associated with reduced-cultivation systems for cereal production in temperate regions.Weed Research 21: 99-109.

Young, A. 1808. General view of agriculture of the count of Sussex. London: Phillips. InLee, H.C. 1995. Non-chemical weed control in cereals. Brighton Crop Protection Conference.Weeds. Vol 3:1161-1170.

Kuebnabm N. 1993. Crop rotation and intercropping strategies for weed management.Ecological Applications 3: 92-122.

Bullock, D.G. 1992. Crop rotation. Crit. Rev. Plant Sci. 11: 309-326.

Loeppky, H.A. and D.A. Derksen. 1994. Quackgrass suppression through crop rotation inconservation tillage systems. Canadian Journal of Plant Science 74: 193-197.

Wyse, D.L. 1994. New technologies and approaches for weed management in sustainableagriculture systems. Weed Technology 8: 403-407.

Walker, R.H. and G.A. Buchanan. 1982. Crop manipulation in integrated weed managementsystems. Weed Science Supplement 30: 17-24.

Leeson, J. Y. 1998. Weed communities and management practices in Saskatchewan farmingsystems. M.Sc. thesis, University of Saskatchewan, Saskatoon. 129 pp.

Funding

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151

9-15 Soil fertility affects weed and crop competition

– B. Frick, E. Johnson - Scott Research FarmProblem

Background

Making nutrients available to the cropgenerally means making nutrients available toweeds. Crops and weeds have the same basicnutrient requirements. How can soil fertility bemanaged to give the greatest advantage to thecrop?

All plants require the same basic nutrients butplants differ in the way they respond to nutrientavailability. They differ in their ability toaccess nutrients because of differences in theirroot structures or mycorrhizal associations.They also can differ in their ability to toleratenutrient imbalances, or in their efficiency atconverting nutrients into growth. Maintainingor improving soil fertility is thus an element ofweed management.

There is an advantage in placing nutrientswhere they are more readily accessed by thecrop than by weeds. Although cropcompetitiveness may improve with improvednutrient status, some weeds are more effective

at utilizing excess resources than are crops.Nutrient levels are generally recommended onthe assumption that herbicides will be used,and that weeds are not an importantconsideration. Lower nutrient availabilitymeans less available for weed growth as wellas for crop growth.

Higher nutrient levels stimulate thecompetitive ability of wild oats, green foxtail

and barnyard grass. Other weeds might belimited by nutrient levels that are adequate forcrop growth. Redroot pigweed, for instance, isespecially sensitive to low phosphorous levels,and will not grow well if phosphorous is

depleted. Wild mustard is also sensitive to

low phosphorous levels, but lamb quartersmay be more abundant in soils with

phosphorous deficiencies. One authorclaimed, after reviewing numerous researchreports on fertilization’s effect on weeds, that"weeds are capable of absorbing nutrientsfaster and in relatively bigger amounts thancrop plants and thus profit more fromfertilization. In the presence of a high weedpopulation density, fertilizer application maystimulate weed growth so greatly that the crop

plants will be overgrown and suppressed."

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Wild oat-wheat competitionexperiments showed that wild oatswere better able to compete withwheat at higher nitrogen levels.Wild oat seed production increasedwith nitrogen, while wheat yielddecreased. Wheat yield increasedwith added nitrogen only if wildoats plants were less than 2% of the

total plant counts. In another study,total weed density (several species)was highest at lowest nitrogen level

in cereal crops. Therefore, resultsfrom experiments investigatingnitrogen effects on weedcompetition have beencontradictory. The effect offertilizer nitrogen on weed-cropcompetition is largely dependent on

fertilizer placement. Generally, instudies where weed growth has beenfavoured over crop growth, thenitrogen has been broadcast.Banding nitrogen close to the seed-row allows the crop roots to useapplied fertilizer more efficientlythan weeds. A number of studieshave been conducted which showthat banding nitrogen can favor the

crop over weeds.

Phosphate fertilizers applied atseeding have been shown to

increase crop competitiveness.Long-term application of manure orother phosphate sources may havesimilar effects. Manure should becomposted to kill most weed seeds.Use soil tests to determineappropriate amounts to add. In onestudy where herbicides were notused, researchers found that soilamendments (cattle manure andpotato compost and alternatingyears of legume green manure)substantially reduced the weedbiomass, possibly by improving

crop competitiveness.

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ConclusionsCompetition between cropsand weeds for nutrients, andfor other factors (light, space,water) at different nutrientlevels, are complex inter-actions that depend on manyfactors - crop species, weedspecies, moisture, nutrientrelease timing, nutrients’positional availability,nutrient ratios, etc. Actionsthat alter nutrient availabilitywill affect the weedcommunity and the crop’scompetitive ability.


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References1

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Sexsmith, J.J. and U.J. Pittmen. 1963. Effect of nitrogen fertilizers on germination and standof wild oats. Weeds 11: 99-101.

Foster, K. 1996. FARMFACTS. Organic Crop Production: Weed Management, SustainableProduction Branch, Saskatchewan Agriculture and Food

Vengris, J., W.G. Colby, M. Drake. 1955. Plant nutrient competition between weeds and corn.Agron J. 47: 213-216.

Hoveland, C.S., G. A. Buchanan and M.C. Harris. 1976. Response of weeds to soilphosphorous and potassium. Weed Science 24: 194-201.

Schipstra, K. 1957. Weeds as indicators of nutritional diseases. Tjdschr. Piziekt. 63: 15-18 inHoveland, C.S., G. A. Buchanan and M.C. Harris. 1976. Response of weeds to soilphosphorous and potassium. Weed Science 24: 194-201.

Alkamper, J. 1976. Influence of weed infestation on effect of fertilizer dressings.Pflanzenschutz-Nachrichten 29: 191-235.

Carlson, H.L. and J.E. Hill. 1985. Wild oat ( ) competition with spring wheat:effects of nitrogen fertilization. Weed Science 34: 29-33.

Jörnsgård, B., K. Rasmussen, J. Hill and J.L. Christiansen. 1996. Influence of nitrogen oncompetition between cereals and their natural weed populations. Weed Research 36: 461-470.

O, Donovan, J.T., K.N. Harker, G.W. Clayton, D. Robinson, R.E. Blackshaw, and L.M. Hall.2001. Implementing integrated weed management in barley ( L.) in R.E.Blackshaw and L.M. Hall eds. Integrated Weed Management: Explore the Potential. ExpertCommittee on Weeds, Sainte-Anne-de-Bellevue, QC. 136 pages.

Blackshaw, R.E., G. Semach, X. Li, J.T. O’Donovan, and K.N. Harker. 2000. Tillage,fertilizer and glyphosate timing effects on foxtail barley ( ) management inwheat. Can. J. Plant Sci. 80:655-660.

Kirkland, K.J. and H.J. Beckie. 1998. Contribution of nitrogen fertilizer placement to weedmanagement in spring wheat ( ). Weed Technol. 12: 507-514.

O’Donovan, J.T., D.W. McAndrew, and A.G. Thomas. 1997. Tillage and nitrogen influenceweed population dynamics in barley. Weed Technol. 11: 502-509.

Hanley, P. 1980. Earthcare: Ecological Agriculture in Saskatchewan. Earthcare Group,Regina. Earthcare

Gallandt, E.R., M. Liebman, S. Corson, G.A. Porter, and S.D. Ullrich. 1998. Effects of pestand soil management systems on weed dynamics in potato. Weed Science 46: 238-248

Avena fatua

Hordeum vulgare

Hordeum jubatum

Triticum aestivum

Funding

Research coordination




153

late-seeded crops, common inorganic systems, and is lessvigorous in cooler situations such asin zero-till, or early seeding.Mature plants vary in size from oneinch to three feet. Large plants canbe quite competitive. Small, verydense plants can reduce surfacemoisture supplies.

Wild oat is an annual cool seasongrass. It has larger seeds, and thusis less prolific. Because the seedsare large, they tend to dry out on thesoil surface, making wild oats morecommon in wet areas, or low spots.Wild oat germinates quickly in coolsoils, and is more competitive atlower temperatures. Thus, it canemerge before the crop and becomevery competitive. Pre-seedingtillage will remove many earlygerminating plants. Later seededcrops may be relatively free of wildoats. Wild oats can be quitecompetitive. Seeds can remaindormant for long periods, making wildoat management a perennial task.

Weed management can be made easierand more effective by considering thecharacteristics of the most commonweeds.

Schreiber, M.M. 1992. Influence oftillage, crop rotation and weedmanagement on giant foxtail (Setariafaberi) population dynamics and cornyield. Weed Science 40: 645-653.

Holzner, W. 1982. Conceptscategories and characteristics of weeds.pp 3-20 W. Holzner and N. Numata,eds. Biology and Ecology of Weeds.W. Junk Publishers, Hague,Netherlands.

Forcella, F. and S.J. Harvey. 1983.Relative abundance in an alien weedflora. Oecologia 59: 292-295 :Ghersa, C.M., M.L. Roush, S.R.Radosevich, and S.M. Cordroy. 1994.Coevolution of agroecosystems and

Conclusions

References1

2

3

in

in

weed management. BioScience 44: 85-94.

Problem

Background

Knowing what weeds are common on aparticular farm will help to determine whatlessons can be learned and what managementstrategies might be effective against them.What can we learn about common weeds tohelp with weed management?

Most weeds have some characteristics incommon. Weeds generally produce largenumbers of seeds. Weed seeds can oftengerminate under a variety of conditions, butsome portion of the seed population remainsdormant. Dormant weed seeds are insuranceagainst conditions that might destroy growingplants. Even though 95% of the weed seeds inthe soil ‘seed bank’ may be lost to germinationor death, the seed bank can often recover in a

single year. Many weeds develop rapidly, areable to self-pollinate, disperse widely andtolerate a wide range of environmental

conditions. A study in 1980 indicated thatdespite enormous effort, weeds have steadily

increased from 1900 to 1980. This trendprobably continues.

Weeds have characteristics unique to eachspecies, so recognizing weed species can beimportant. Many sources are available to help

with weed identification.

Several weed characteristics have beensummarized in Table 1. Let’s compare wildoats and green foxtail as an example of whatwe can learn from these characteristics.

Green foxtail (commonly known as wild milletor pigeon grass) is an annual grass with smallseeds that birds seem to love. As with mostweeds, seed production can be prolific. Seedsthat germinate on the soil surface, or in surfacechaff, often have trouble rooting, so thesespecies can be less abundant in zero-tillagesystems. Root development, even within thesoil is not extensive. Therefore, harrowing isoften an effective means of control. Greenfoxtail is a warm season grass. It germinatesmore quickly and is more competitive at highertemperatures. Thus, it is more aggressive in

1

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3

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4

5

6

7

8

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11

Anonymous. 1998. Weeds ofthe Prairies. AlbertaEnvironment Centre and AlbertaAgriculture

Anonymous. 1986. WeedSeedling Identification Guide.Saskatchewan Agriculture andFood.

Looman, J. and K.F. Best.1981. Budd's Flora of theCanadian Prairie Provinces.Agriculture Canada

Anonymous. 1998. FieldScouting Guide. First steps inintegrated pest management.Insects, diseases, weeds.Canada-Manitoba Agreement onAgricultural Sustainability.

Anonymous. 1994. PracticalCrop Protection. Weeds InsectsDiseases. Alberta AgricultureFood and Rural DevelopmentPublishing Branch.

Chepil, W. S. 1946.Germination of weed seeds II:The influence of tillagetreatments on germination. Sci.Agr. 26: 347-357.

Saskatchewan Pulse CropDevelopment Board. 1995.Pulse Production Manual.Saskatchewan Agriculture andFood.

Hanley, P. 1980. Earthcare:Ecological Agriculture inSaskatchewan. Earthcare Group,Regina

–Agri-Food Innovation Fund


Funding

Review coordination

Canada-Saskatchewan

9-16 Weed characteristics– B. Frick. E. Johnson - Scott Research Farm


154


Table 1. Some characteristics of the most common weeds in Saskatchewan.7, 8, 9, 10, 11

Weed

Wild oats

Green foxtail

Wild buckwheat

Stinkweed

Canada thistle

Lamb's quarters

Perennial sow-thistle

Russian thistle

Wild mustard

Redroot pigweed

Shepherd's purse

Kochia

Dandelion

Quack grass

* A = annual, W = winter annual, P = perennial** Yield loss estimates for weed number per metre squared in wheat. Example: 10 wild oats per metre squared caused a wheat yield loss of 10%.

For perennial plants, losses are expressed per shoot rather than per plant, because it is difficult to recognize distinct plants in the field.

Life *history

A

A

A

A, W

P

A

P

A

A

A

A, W

A

P

P

Seeds/plant

250

5,000

1,200

15,000

700

72,000

10,000

---

3,500

---

38,500

14,600

---

---

Germination

Early

Late

Early

Spring / fall

Medium

Early

---

Early

Early, continual

Late, warm

Spring / fall

Early

---

---

Dormancy

Long

Short

Medium

Medium

Medium

Long

---

Medium

Very long

Long

Medium to long

Short

---

---

Maturity

Medium

Early

Medium

Medium to long

Late

Late

---

Mid to late

Early to late

Late

Early

---

---

---

Preference

Wet or lowspots

Cultivatedareas

---

---

Field edges

Organic soils

Moist, fertile

Drier sites

Cool, moist

Fertile soil

---

---

Field edges

---

Yield **losses

10% for 10

Varies withsize

22% for 30

20% for 750

38% for 14 shoots

25% for 200in barley

No estimate

No estimate

35% for 100

No estimate

No estimate

No estimate

No estimate

10% for 100 shoots

Management

Delayedseeding

No-till, early seedingharrowing

Delayed seeding

Fall/spring tillage

Fall tillage, mowing

Harrowiing

Mowing, tillage

Strong competition

---

Establish crop early

Fall/spring tillage

Delayed seeding

Tillage deeperthan 2 inches

Tillage, mowingspring/fall

155

9-17 Field pea – manage seeding for best pre-emergence weed control


Problem

Background

It is recommended that field pea be seededearly and at a depth of 5 - 7.5 cm. Organicproducers often delay seeding and use pre- orpost-seeding tillage to remove germinatedweeds. Crops that emerge before weedemergence are more competitive than cropsemerging at the same time or after weedemergence. Delayed seeding to control late-emerging weeds and seeding at shallowerdepths to promote rapid crop emergence maybe an alternative weed management strategy.What combination of seeding date, seed depth,and pre-emergence weed control optimizesfield pea yield when grown without herbicideuse?

Organic producers use several cultural and

mechanical methods to manage weeds. Priorto introduction of selective herbicides,secondary tillage combined with delayedseeding was commonly recommended to

control wild oat. Research conducted from1952 to 1957 at seven locations in westernCanada found that tillage and delayed seedingcontrolled greater than 70% of wild oat in

wheat and barley. A Minnesota study foundthat pre-plant tillage just prior to delayedsoybean planting resulted in reduced weed

populations. Delayed seeding may beeffective in controlling some weed species, butit normally results in lower yields for many

crops. Field pea production has been shownto be viable in the brown and dark brown soilzone of Saskatchewan, provided that seeding

is completed before mid-May. In BritishColumbia, delayed seeding reducedprocessing pea yield at a location where themean maximum growing season airtemperature exceeded 21° C, but had no effect

at location with lower air temperatures.Delayed seeding and secondary tillage iscommonly used by organic growers in spite of

the potential yield decline.

1

2

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5

6

7

1

Most weed seeds emerge fromshallow depths (< 2 cm) and largeseeded crops can be seeded deepallowing for selective mechanicalweed control between seeding time

and crop emergence.

Pavylchenko observed that pre-emergence tillage gave crops abouta ten-day weed free period.

Our field experiment was conductedon cultivated cereal crop stubble atthe Scott Research Farm from 1999to 2001. Treatments of seeding date(early May, mid-May and late May),seed depth (2.5 cm and 7.5 cm) andweed control (none, pre-emergencetillage, and herbicide) were appliedin a split-plot experimental design.Each treatment was replicated fourtimes. Wild oats and wild mustardwere seeded just before the earliestseeding date followed by a shallowcultivation to distribute weed seedsand manage crop residue. Weseeded field pea ( Grande) at atarget plant density of 80 pea plants

m with a narrow opener hoe-drillequipped with on-row packing. Wedid pre-emergence tillage aboutthree to five days after seeding, butthe second tillage sometimes had tobe delayed up to 10 days dependingon weather conditions. Pre-emergence tillage was accomplishedin the shallow seeded plots (2.5 cm)with a tine harrow while a rod-weeder was used for the deepseeded plots (7.5 cm). Datacollection included field pea density,weed density, weed biomass, andcrop yield.

8 ,9

1 0

-2

Study description

cv

Major findingsCrop establishment was verygood in all years with plantdensities exceeding 70

plants/m (data not shown).Overall, seeding date andseeding depth did not have aneffect on crop establishment.Field pea was not damagedby pre-emergence tillage asthe treatments did not reducefield pea density. In somecases, deep seeding delayedcrop emergence (date atwhich distinct crop rows werevisible) by one day.However, emergencedifferences did not affect timeto crop maturity.

Pre-emergence tillage did notresult in a detectablereduction in weed biomass atthe early May seeding datesince very few weeds hademerged (Table 1).Herbicides effectivelyreduced weed biomass at allseed dates. Pre-emergencetillage was effective inreducing weed biomass at thedelayed seeding dates, withthe pre-emergence rod-weedtreatment resulting in weedfresh weight reductionssimilar to herbicidetreatments. Pre-emergenceharrowing was not aseffective as pre-emergencerod-weeding in reducingweed biomass at delayedseeding dates. Deep seedingprovided some weed controleffect at the late May seedingdate since the seedingimplement was able to uprootand bury more weeds whenset at a 7.5 cm depth.

-2


156

Seeding delayed until lateMay resulted in yielddeclines of up to 37% (Table2). Previous research hasshown that seeding field peain late May compresses theflowering period resulting in

lower yields.

Pre-emergence tillageresulted in small crop yieldincreases at the early Mayseeding date; however, itprovided yields equivalent toherbicides at the mid-Mayseeding date. At the mid-May seeding date, yieldsachieved by pre-emergencetillage resulted in 80% of thehighest yield achieved withearly seeding and herbicideapplication. At the late Mayseeding date, pre-emergencetillage improved field peayields by 30 to 35% with pre-emergence rod-weedingproviding higher yields thanpre-emergence harrowing.

Though pre-emergencetillage improved field peayield at the late May seedingdate, these yields were stilllower than the untreatedchecks seeded in early May.Shallow seeding did notimprove field pea competi-tiveness at any seed date.Deep seeding resulted inhigher yields at both the earlyand late May seeding date,but not at the mid-Mayseeding date.

We don't fully understand thereason for higher yields withdeep seeding at the early seeddate. However, we believethat deep seeding mayprovide a better environmentfor bacteriasurvival, resulting inimproved nitrogen fixation.Improved yield from deep

6

Rhizobium

seeding at the late May date islikely due to the weed control effectdescribed earlier. Organic growersmay be able to achieve adequateweed control and satisfactory yieldswith a slight delay in seeding datefollowed by pre-emergence tillage,but a long delay in seeding iscounter-productive.

Pre-emergence tillage betweenseeding time and crop emergencecan be very effective in reducingweed density and preventing yieldloss provided there is adequateweed growth at tillage time. Astrategy for producers who choosenot to use herbicides would be toconduct early spring tillage tostimulate weed emergence, wait 10- 12 days and then seed at a 7.5 cmdepth. Follow this with pre-emergence rod-weeding five toseven days after seeding.

Conclusions


Table 1. Interaction effects of field pea seeding date, seed depth, and weed control system onweed biomass at Scott -- 1999-2001.

Depth

LSD

2.5 cm

7.5 cm

* LSD (P=0.05) to separate weed control means within hte same seed depth and seeding date.

Treatment

UntreatedPre-emerge harrowHerbicideUntreatedPre-emerge rod-weedHerbicide

Early MayMay 2-6

7146229974965631

(grams/m )Mid May

195*

Weed biomass2

May 14 - 18

707478186781183183

Late MayMay 30 - June 1

933567209656315314

Table 2. Interaction effects of field pea seeding date, seed depth, and weed control system onfield pea yield at Scott -- 1999-2001.

Depth

Seeding date meansLSD

2.5 cm

7.5 cm

* LSD (P=0.05) to separate seeding date means** LSD (P=0.05) to separate weed control means within the same seed depth and seeding date.

Treatment

UntreatedPre-emerge harrowHerbicideUntreatedPre-emerge rod-weedHerbicide

Early May

2393146*

May 2-6

175819332930216322143363

(kg/ha)Mid May

2510242**

Crop yield

May 14 - 18

207627382719205927372729

Late May

1585

May 30 - June 1

110314372032134017951807

References

Funding


1

2

3

4

5

6

7

8

9

1 0

Beckie, M.A.N. 2000. Zero-tillage and organicfarming in Saskatchewan: An interdicisiplinarystudy of the development of sustainable agriculture.PhD Thesis. University of Saskatchewan,Saskatoon, SK.

Brown, D.A. 1953. Wild oats - progress incultural control. Weeds 2: 295-299.

Canada Department of Agriculture. 1959. Effectof delayed seeding on yield of wheat and barley andwild oat control in the prairie provinces. CanadaDepartment of Agriculture Publication 1044.Ottawa, ON.

Robinson, R.G. and Dunham, R.S. 1956. Pre-plant tillage for weed control in soybeans. Agron.J. 48: 493-495.

Anderson, C.H. and Hennig, A.M.F. 1964. Theeffect of date of seeding and fertility level on theyield of wheat, oats, and barley in northwestAlberta. Can. J. Plant Sci. 44: 15-20.

Miller, P.R., Brandt, S.A., Slinkard, A.,MacDonald, C., Derksen, D., and Waddington, J.1998. New crop types for diversifying andextending spring wheat rotations in the brown anddark brown soil zones of Saskatchewan. FinalReport. Canada-Saskatchewan Agriculture GreenPlan Agreement. 134 pp.

Fletcher, H.F., Ormrod, D.P., Maurer, A.R., andStanfield, B. 1966. Response of peas toenvironment. I. Planting date and location. Can. J.Plant Sci. 46: 77-85.

Mohler, C.L. 1996. Ecological basis for thecultural control of annual weeds. J. Prod. Agric. 9:468-474.

Mohler, C.L. and Galford, A.E. 1997. Weedseedling emergence and seed survival: Separatingthe effect of seed position and soil modification bytillage. Weed Res. 17: 147-155.

Pavlychenko, T.K. 1949. Plant competition andweed control. Agr. Inst. Rev. 4: 142-145.



157


158

Weed burial effectiveness depends on soiltexture, weed growth stage, plant architecture,harrowing speed and depth, harrow setting, soilmoisture and number of passes. Fine-texturedsoils have a higher mechanical resistance thancoarse-textured soils, which impedes recovery

of buried plants. The plant’s ability toresist bending is important in tolerating post-emergence harrowing as bent plants are more

easily buried. Therefore, plants inadvanced growth stages tolerate post-emergence harrowing better than seedlings.Weeds that form a rosette with their meristemclose to the soil surface are more sensitive toburial than erect weeds with their meristems

above ground level.

Soil coverage increases in proportion to

harrowing depth. Weed control due toharrowing will be spatially variable in a field,as working depth and soil cover will fluctuatein response to soil conditions. Weed burial bya tine implement may vary due to ridgesformed by the back row of tines. Kurstjens and

Perdok reported that up to 80% of weeds werecovered by ridges between the tines; however,the trench left by the tine covered less than30% of weeds. This may be why multiplepasses tend to result in more efficacious weedcontrol as subsequent harrow passes may fillthe trenches with soil.

The amount of soil disturbance a harrowcauses is controlled by the angle of the harrowtine in relation to the soil surface. A forwardpointing tine was found to cause 42% morehorizontal transport of soil than a backward

pointing tine. The distance soil aggregatesmove is proportional to the square of the toolvelocity. Therefore, increased harrow speedsresult in more uniform soil covering of weeds

but do not necessarily increase burial depth.Faster harrow speeds do not improveselectivity as they increase soil burial of both

weeds and crop.

Soil moisture’s effect on post-emergencemechanical tillage efficacy is not clear. Incontrolled environment studies, moisturecontent did not affect survival of four weed

species if they were completely buried.

1 6 ,1 3

1 4 ,1 3 ,11

1 3

1 7

11

1 8

1 9

1

1 4

Wild oat can emerge from greaterdepths than most other weed speciesbut pre-emergence tillage can stillbe effective. Wild oat has amesocotyl that extends the growingpoint meristem away from the seed

to near the soil surface. In cerealcrops, the mesocotyl remains closeto the seed, protecting the growingpoint from mechanical injury.

Fifty-two percent of organicgrowers surveyed in Saskatchewanuse post-emergence harrowing as a

weed control practice. Post-emergence tillage generally has lowselectivity as the negative cropcovering effect can offset the

positive weed killing effect.

Studies in Europe show that theprimary action with post-emergenceharrowing is burying plants withsoil and less than 25% of the weeds

are uprooted by the treatment. Theamount of soil burial required tocontrol many weed species varies

between two and three cm. Thismay be difficult to achieve in thefield as it was found that less than10% of harrowed plants were buried

deeper than 1.5 cm. Partially

buried plants generally survive,although dry soil conditions mayincrease the mortality of partially

buried plants.

Sensitivity to soil burial is related to

seed size. Small-seeded plantsexhibit greater mortality whenburied, particularly in early growthstages. The small seeded plants relyheavily on photosynthesis to supplytheir energy needs, while large-seeded plants can draw on seed

reserves in early growth stages.

8

9

1 0

11

1 2 ,1 3

11

1 3

1 4

1 3

3 ,1 5

Problem

Background

Some form of mechanicalweed control is generallyused by most organicproducers. Post-emergenceweed control with animplement such as a harrowor a rotary hoe may controlweeds, but does not alwaysimprove crop yields. If weedinterference is reduced, thenwhy aren’t crop yields alwaysimproved?

Selectivity is defined as theratio between weed control

and crop injury. In general,mechanical weed control ismost selective when the cropsdiffer from weeds in growthhabit, emergence time and

maturity time. Weeds with ashort specific germinationperiod are more easilycontrolled mechanically thanweeds that germinate over a

long time period. Largeseeded crops can be seededdeep which allows highlyselective mechanical weedcontrol between seeding time

and crop emergence. Mostweed seeds emerge from thetop two cm of soil with themaximum emergence depth

at six cm. This techniquecan provide effective weedcontrol and give the crop a

competitive advantage.

Pavlychenko observed thatpre-emergence tillageprovided the emerged cropwith about a ten-day weedfree period.

1

2

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3

4

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9-18 Selectivity - an important concept in mechanical weed control



159

Dry conditions were very effective inimproving mortality if plants were pulled fromthe soil and the roots were re-buried. Goodsoil moisture conditions might have resulted inthe differential ability of spring wheat and wild

oat to recover from harrowing. Above-normal precipitation and good soil moistureconditions at and following harrowing werereported in the one year where harrowingimproved spring wheat yield. The effect of soilmoisture on harrowing efficacy may also be

dependent on the weed species.

Multiple harrow passes may be required to

achieve some level of weed control. A

model developed by Rasmussen suggestedthat up to three harrow passes provided theoptimum level of weed control and yieldresponse in field pea. Four to five consecutiveharrow passes in winter wheat were required to

achieve up to 95% weed control. Threepasses reduced weed biomass by about 75% in

spring barley.

Deep harrowing, high soil disturbance, andmultiple passes may cause more weed burial;however, selectivity is not necessarilyimproved as there is generally a proportional

increase in crop burial. Under low weedpopulations, increased crop covering due toconsecutive harrow passes resulted in a declinein spring barley yields of 0.12 to 0.15% forevery unit percentage of crop cover. Tominimize crop injury, it is usuallyrecommended that harrowing be conducted in

the same direction as crop rows. However,

Wilson found that harrowing directionhad no impact on weed control or crop injuryin winter wheat.

Harrowing may be more selective at the crop’slater growth stages, provided the weeds are in

early developmental stages. Four passes witha flex-tine harrow resulted in up to 90% controlof small broadleaf weeds with no damage towinter wheat when it was harrowed at a heightof 20 to 25 cm. The established crop was ableto push the tines sideways where inter-row

weeds were controlled. Wilson alsoreported that winter wheat tolerated harrowingin the spring, but autumn harrowing causedsevere crop injury.

2 0

11

2 0 ,2 1 ,2 2

2 3

2 4

2 2

1 0

2 5

2 1

2 4

2 1

et al.

et al.

Overall, yield responses to post-emergence harrowing have beenmodest due to low crop-weed

selectivity. Kirkland reported a19% spring wheat yield increase inone year of a three-year study. InDenmark, post-emergenceharrowing resulted in spring wheatyields ranging from 91 to 118% of

the untreated check. Yieldresponse in winter wheat has ranged

from 0 to 10%. A model forharrowing in field pea suggestedyield responses in the range of 0 to5% corresponding to 0 to 70% weed

control. However, Al-Khatib

reported that post-emergencecultivation with a finger weederresulted in an 18% yield increase infield pea. Weed control levels inharrowed spring barley averagedabout 75%; however, yield

responses did not exceed 10%.

Models developed by Rasmussensuggest that crop yield response willbe greater under high weedpressure, as the positive weed-killing effect will outweigh thenegative crop damage.

Organic growers who usemechanical weed control techniquesshould time their operations tomaximize selectivity. Pre-emergence tillage in deep seededcrops can result in highly selectiveweed control. Post-emergenceharrowing has low selectivity,therefore organic growers need toscout their fields to determine if thepractice is justified. If post-emergence harrowing is warranted,every attempt should be made tominimize crop injury.

2 0

2 6

2 1 ,2 4

2 3

2 7

2 2

1 0

et

al.

Conclusions

Funding

Further information –

– Canada-Saskatchewan Agri-Food Innovation Fund



160

References1

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3

4

5

6

7

8

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1 0

11

1 2

1 3

1 4

1 5

1 6

1 7

Rasmussen, J. 1990. Selectivity, an important parameter on establishing theoptimum harrowing technique for weed control in growing cereals. p. 197-204. Proceedings of the 1990 European Weed Research SocietySymposium, Integrated weed management in cereals. Helskinki, Finland.

Zimdahl, R.L. 1993. . Academic Press. SanDiego.

Mohler, C.L. 1996. Ecological basis for the cultural control of annualweeds. J. Prod. Agric. 9: 468-474.

Mohler, C.L. and A.E. Galford. 1997. Weed seedling emergence and seedsurvival: Separating the effect of seed position and soil modification bytillage. Weed Res. 17: 147-155.

Brown, D.A. 1953. Wild oats -progress in cultural control.

Rasmussen, J. 1996. Mechanical weed management. p. 943-948Proceedings of the Second International Weed Control Congress. Vol. III.Copenhagen, Denmark.

Pavlychenko, T.K. 1949. Plant competition and weed control. Agr. Inst.Rev. 4: 142-145.

Fryer, J.D. and S.A. Evans. 1972. Weed Control Handbook Vol. 1. 5thEdition. Blackwell Scientific Publications. Oxford.

Beckie, M.A.N. 2000. Zero-tillage and organic farming in Saskatchewan:An interdisciplinary study of the development of sustainable agriculture. PhDThesis. University of Saskatchewan, Saskatoon, SK.

Rasmussen, J. 1991. A model for prediction of yield response in weedharrowing. Weed Res. 31: 401-408.

Kurstjens, D.A.G., and U.D. Perdok. 2000. The selective soil coveringmechanism of weed harrows on sandy soil. Soil Tillage. Res. 55:193-206.

Terpstra, R. and J.K. Kouwenhoven. 1981. Inter-row and intra-row weedcontrol with a hoe-ridger. J. Agric. Engng. Res. 26: 127-134.

Baerveldt, S. and J. Ascard. 1999. Effect of soil cover on weeds. Biol.Agric. Hort. 17: 101-111.

Jones, P.A. and A.M. Blair. 1996. Mechanical damage to kill weeds. p.949-954. Proceedings of the Second International Weed Control Congress.Copenhagen, Denmark.

Cavers, P.B. and M. Kane. 1990. Responses of proso millet () seedlings to mechanical damage and/or drought treatments.

Weed Technol. 4: 425-32.

Cussans, G.W., S. Raudonius, P. Brain, and S. Cumerworth. 1996. Effectsof depth of seed burial and soil aggregate size on seedling emergence of

, and wheat. WeedRes. 36: 133-141.

Sogaard, H.T. 1998. Automatic control of a finger weeder with respect tothe harrowing intensity at varying soil structures. J. Agric. Eng. Res. 70:157-163.

In

Fundamentals of weed science

In

In

Panicummilliaceum

Alopecurus myosuroides Galium aparine, Stellaria media,

Weeds 2: 295-299.

1 8

1 9

2 0

2 1

2 2

2 3

2 4

2 5

2 6

2 7

Kouwenhoven, J.K. and R. Terpstra. 1979.Sorting action of tines and tine-like tools in thefield. J. Agric. Eng. Res. 24: 95-113.

Rydberg, T. 1993. Weed harrowing - drivingspeed at different stages of development. Swed. J.Agric. Res. 23: 107-113.


Wilson, B.J., Wright, K.J., and R.C. Butler. 1993.The effect of different frequencies of harrowing inthe autumn or spring on winter wheat, and thecontrol of (L.) vill.,L. and L. Weed Res. 33: 501-506.

Rasmussen, K. and J. Rasmussen. 2000. Barleyseed vigour and mechanical weed control. WeedRes. 40: 219-230.

Rasmussen, J. 1993. Yield response models formechanical weed control by harrowing at earlygrowth stages in peas ( L.). WeedRes. 33. 231-240.

Rasmussen, J. 1991a. Optimizing the intensity ofharrowing for mechanical weed control in winterwheat. p. 177-184. Proceedings of the 1991Brighton Crop Protection Conference, Weeds.Brighton, U.K.

Foster, K. 1986. Organic crop production: Weedmanagement. Saskatchewan Agriculture and FoodFarmFacts. Regina, Saskatchewan.

Rasmussen, J. 1992. Testing harrows formechanical control of annual weeds in agriculturalcrops. Weed Res. 32: 267-274.

Al-Khatib, K., C. Libbey, and R. Boydston. 1997.Weed suppression with green manurecrops in green pea. Weed Sci. 45: 439-445.

Stellaria media Galium aparineBrassica napus

Pisum sativum

In

Brassica


161

9-19 Evaluating – an organic herbicideInterceptor

– E. Johnson - Scott Research Farm– K. Sapsford, R. Holm - University of Saskatchewan, Saskatoon

– R. Kutcher - Melfort Research Farm– W. May, G. Lafond - Indian Head Research Farm

– T. Hogg - Canada - Saskatchewan Irrigation Crop diversification Centre, Outlook– B. Nybo - Wheatland Conservation Area Inc., Swift Current– S. Anderson - East Central Research Foundation, Canora

– J. McConnell - South East Research Farm, Redvers

Problem

Background

Organic producers are not allowed to usesynthetic pesticides in their production system.However, herbicides derived from naturalsources may be allowable. Interceptor is aherbicide registered and certified for organicproduction in New Zealand. A non-selectiveorganic herbicide could be very useful inreplacing pre-seeding or pre-emergencetillage. This study’s objectives were: 1) toevaluate Interceptor’s efficacy in controllingannual indicator weeds, and 2) to defineapplication parameters that may improveInterceptor’s efficacy.

Interceptor is a non-selective, contact herbicidederived from an extract of pine oil. Since theherbicide kills by contact, uniform spraydeposition on the target plant is required formaximum efficacy. We did preliminarygreenhouse and field studies to evaluateInterceptor’s efficacy in organic field cropproduction, using canola and tame oat asindicator ‘weeds’ in both studies. Preliminarygreenhouse studies were done at the ScottResearch Farm. Interceptor applicationresulted in quick desiccation of canola plantsbut had little activity on oat plants in thegreenhouse studies. This is likely due to thecontrasting leaf orientations of canola and oat.Canola's broader leaves are horizontallyoriented, while oat has thin, vertically orientedleaves. Broad, horizontal leaves receive morespray droplets and the spray is more likely tobe retained on the leaf. Greenhouse studiesalso suggested that weed control withInterceptor could be improved by increasingcarrier volume from 10 gpa to 20 gpa.

Study descriptionField studies were conducted at allSPOKE sites plus the Kernen CropResearch Farm at Saskatoon.Canola and oat were seeded at target

densities of 150 and 200 plants mrespectively. Plot size varied bylocation. Interceptor was applied atthree rates: 10%, 20% and 30% v/vconcentration. Included in the studywere an untreated check and anindustry standard (glyphosate).Glyphosate rates were 0.25, 0.50and 0.75 liters/acre. Interceptor wasapplied with standard sprayingequipment using a carrier volume of20 gpa. Glyphosate was applied at5 to 10 gpa. Herbicides wereapplied when the plants were in thethree-to-five leaf stage.Experimental design was arandomized complete block.

Visual control ratings (0 to 100%control) were taken three, seven,and 14 days after application. Plantbiomass data were collected 14 to21 days after seeding.

-2

Major findingsTrends were similar for alllocations -- we combineddata. Interceptor causedsome leaf burn on oats, butcontrol ratings averaged lessthan 10% (Table 1). Therewas no significant reductionin wild oat biomass fromInterceptor treatments at allrates. Since Interceptor isstrictly a contact herbicide,spray coverage is critical.Oat has a narrow leaf with avertical orientation, thereforespray retention is generallylow. Interceptor gave slightlybetter results on canola, butoverall control was still notsatisfactory (Table 2).Interceptor was very fastacting on canola -- symptomsappeared within a few hours.Initial control ratings forInterceptor were higher thanfor glyphosate. However,significant regrowth occurredone to two weeks afterInterceptor application. Finalcontrol ratings for Interceptorranged from 10 to 26%depending on rate. The 30%Interceptor rate resulted inabout a 22% reduction incanola fresh weight, relativeto the untreated check.Glyphosate application atrates above 0.50 liter/acreresulted in a 99% reductionin both oat and canola freshweight.


162

ConclusionsInterceptor herbicide is noteffective as a non-selectiveherbicide using conventionalfield application technology.Control may be slightlyimproved with flooding typenozzles that improves spraycoverage; however, it isdoubtful that small changesin application technologywould result in an acceptablelevel of weed control. Highrates of active ingredient arerequired with Interceptor,which would further reduceits applicability in extensivefield crop production.

In spite of its limitations forfield crop production,Interceptor herbicide mayhave potential as a herbicidefor the domestic market.Many urban municipalitiesare restricting the use ofpesticides. In an urbansituation, the highconcentration required is notan issue due to the smallareas usually treated. Sincedomestic application isusually done with a handsprayer, spray coverage maybe improved. Homeownerswho wish to use a herbicidederived from a natural sourcemay find the fast actingnature of the herbicideappealing -- symptomsappear in hours.

Funding





Table 1. Efficacy of Interceptor and Glyphosate in the control of tame oat.Mean of eight Saskatchewan locations -- 2001.

Treatment

Check - untreatedInterceptor 10%Interceptor 20%Interceptor 30%Glyphosate 0.25 L/acreGlyphosate 0.50 L/acreGlyphosate 0.75 L/acre

% VisualControl3 DAT

0.04.46.615.98.413.818.1


0.02.45.19.867.186.491.3

LSD0. 05


0.03.25.49.687.695.599.5

71

Weedbiomass

g/m2

538.4535.7511.3519.92.71.52.8

Table 2. Efficacy of Interceptor and Glyphosate in the control of canola.Mean of eight Saskatchewan locations -- 2001.

Treatment

Check - untreatedInterceptor 10%Interceptor 20%Interceptor 30%Glyphosate 0.25 L/acreGlyphosate 0.50 L/acreGlyphosate 0.75 L/acre


0.013.133.149.710.314.118.8


0.014.630.536.451.475.579.9

LSD0. 05


0.09.820.226.672.388.191.8

94

Weedbiomass

g/m2

497.2558.2435.4388.747.70.70.3

163

References1

2

3

4

Kirkland, K.J. 1993. Weed management in spring barley () in the absence of herbicides. J. Sust. Agric. 3: 95-104.

O’Donovan, J.T., K.N. Harker, G.W. Clayton, and L.M. Hall. 2000. Wildoat (Avena fatua) interference in barley (Hordeum vulgare) is influenced bybarley variety and seeding rate. Weed Technol. 14: 624-629.

Townley-Smith, L. and A.T. Wright. 1994. Field pea cultivar and weedresponse to crop seed rate in western Canada. Can J. Plant Sci. 74: 387-393.

O’Donovan, J.T. 1994. Canola ( ) plant density influencestartary buckwheat ( ) interference, biomass, and seedyield. Weed Sci. 42: 385-389.

Hordeumvulgare

Brassica rapaFagopyrum tataricum

Funding




Major findings

Conclusion

Extremely high weed populationsseverely reduced lentil yield in2000, while 2001 yields were muchbetter under natural weed popula-tions. In spite of low yields in 2000,yield trends were similar for bothyears and data were combined.Lentil yield increased as seedingrate increased at the 11, 22 and 33cm row spacings (Figure 1). At the44 cm row spacing, increased

seeding rate above 60 kg ha had noeffect. Optimum seed rate for lentilgrown in the presence of weeds

approached 150 to 200 kg ha .

Organic producers should considerseeding in a narrow row spacingcombined with increased seedingrates. If narrow rows are notpractical, then producers should usea seeding implement that distributesseed in a wide row band.

Optimum seed rate for lentil underweedy conditions was approxi-mately 1.5 - 2.0 times the currentrecommended seeding rate forconventional producers.

-1

-1

Problem

Background

Study description

Pulse crops such as lentils compete poorlywith weeds. Post-emergence harrowing maybe used; however, this can cause damage andresult in higher levels of disease such asAscochyta blight. This study’s objective wasto assess various row spacings (11, 22, 33, and44 cm) and seeding rates (30, 60, 120, and 240

kg ha ) to improve competitiveness oforganically grown lentil.

Farmers attempting to minimize negativeeffects of uncontrolled weeds often considerusing narrower row spacings and higherseeding rates. Spring barley seeded in 33 cmrows and not treated with herbicides had 46%and 55% higher wild mustard biomasscompared to barley seeded in 11 and 22 cm

rows, respectively. Increasing barley seed rate

from 85 kg ha to 200 kg ha reduced wild oat

dry matter and seed production. Increasingfield pea seeding rate reduced weed densities

and improved crop yield at Melfort. Researchconducted in Alberta shows that increasedcanola seeding rates can reduce the

competitive effect of tartary buckwheat. Weanticipate that narrower row spacings andhigher seeding rates will improve the yield oforganically grown lentil.

The study was conducted in both 2000 and2001 on a tilled fallow site that received anearly spring cultivation. Glamis lentil wasseeded with a hoe-drill plot seeder equippedwith on-row packing. In the 2000 trial, weedswere seeded into the test area prior to seedinglentil. In 2001, lentil was seeded into alocation known for its high natural density ofannual weeds. Wild oat, wild mustard, lambsquarters and stinkweed made up most of theweed population in both years. The experimentwas conducted according to a split plot designwith row spacings (11, 22, 33, and 44 cm) asthe main plot factor and seeding rate (30, 60,

120, and 240 kg ha ) as the subplot factor.Treatments were replicated four times. Subplotsize was 2 m x 5 m. No post-emergenceherbicides were applied. Data collectedincluded only lentil seed yield.

-1

1

-1 -1

2

3

4

-1

9-20 Organic lentil production – optimum seeding rate, row spacing



164

Figure 1. Mean lentil yield response to effects of row spacing and seeding rate -- lentil growing underweedy conditions -- Scott -- 2000 - 2001.

700 -

600 -

500 -

400 -

300 -

200 -

100 -

0 -

Yie

ld(k

g/ha

-1)

Row spacing (cm)

11 cm 22 cm 33 cm 44 cm

Seed rate -- kg/ha

30

60

120

240

Error bar represents the LSD to separate the seeding rate means within each row spacing.0. 05

600 -

500 -

400 -

300 -

200 -

100 -

0 -

0 50 100 150 200 250 300

Yie

ld(k

g/ha

)-1

Seed rate (kg/ha )-1

- - - - - - -

Figure 2. Effect of seed rate on lentil yield (kg/ha) grown inweedy conditions. Seed rate means are the meanof two years of data and three row spacings (11, 22,33 cm) where row spacing had an effect.Scott -- 2000 - 2001


Although variable, clippingreduced subsequent weedseedling emergence.Clipping in 1999 reducedwild oat emergence thefollowing spring if theclipping occurred after wildoat heading (Figure 2). In the2000 - 2001 study, wild oatpopulations were low andclipping did not cause asignificant reduction inemergence.

There was no detectabledifference in wild mustardrecruitment in the 1999 -2000 study, but there was atrend towards lower densitieswhen the wild mustard wasclipped at the podding stage(Figure 3). Many of the podsformed below the cropcanopy in the first year of thestudy, which reduced theefficacy of clipping.Clipping at anyy weed stagewas effective in reducingwild mustardd recruitment inthe 2000 - 2001 study (Figure3). Recruitment of lambsquarters showed similarresults (Figure 4).

Field studies conducted byPAMI showed similar trendsto the Scott trials (Table 1).

PAMI field trials

Problem

Background

Weed control is a challenge for organicgrowers. Organic producers rely on croprotation, cultural practices, and mechanicalmeans to control weeds. Weeds in short staturecrops such as flax and lentil can be particularlyproblematic. This study’s objectives were: 1)to develop or modify field equipment thatcould clip weeds above the crop canopy, 2) todetermine if weed clipping improves cropyield, and 3) to determine if weed clippinginfluences weed seedling densities in thesubsequent growing season.

Some organic producers have experimentedwith clipping weeds above the canopy of shortstature crops such as lentil or flax. Whileclipping weeds may provide some aestheticvalue, it is not known whether the practice willaffect crop yield or weed seed return to the soilseed bank. A project was initiated in 1999 todevelop or modify equipment for weedclipping and to evaluate whether the practiceimproved crop yield and/or reduced weedseedling recruitment the following growingseason. At Scott, a field experiment wasconducted over two years where clipping atvarious stages of weed development wasevaluated. Clipping was done above a lentilcrop canopy with a gas-powered hedgetrimmer. The Prairie Agriculture MachineryInstitute (PAMI) at Humboldt modified thecutting component of a self-propelled swatherand carried out field trials on four farm fields.

Study description

Major findings

Scott experiment

Chenopodium album

PAMI field trials

Scott experiment

�

�

�

�

�

�

�

�

�

�

�

Conducted in 1999 and 2000Experimental design: RCBDCDC Glamis lentils seeded onMay 18, 1999 and May 8, 2000Lentil seeded in 22 cm rows at a

rate of 130 kg/haWild oat and wild mustard seeded

at a density of 100 seeds/mbetween the crop rowsClipping done at these timings:-- 1 -- Wild mustard in full

flower/ Wild oat in boot stage;-- 2 -- Wild mustard podded/

Wild oat headed;-- 3 -- Wild mustard seed watery-

ripe/ Wild oat mid-dough stage;Herbicide and unclipped weedychecks were included.Herbicide treatment: post-emergence sequential application

of metribuzin (212 g ai/ha )

sethoxydim ( 212 g ai/ha ).

Data collection included crop yieldand wild mustard and wild oatseedling emergence the following

spring (plants m ) prior to seeding.In the spring of 2001, lambsquarters ( L)emergence was also recorded.

Fields were clipped above a lentil orflax crop with a modified swather.Each field also had an unclippedcheck strip.

Weed clipping did not result in adetectable lentil yield increase ineither year (Figure 1). Clippingmust be postponed until the weedselongate above the crop canopy.Most of the yield loss associatedwith weed competition occurs inearly crop development stages.

-1

-2

-1

-1

-2

9-21 Clipping weeds above a crop canopy

– E. Johnson - Scott Research Farm– G.E. Hultgreen - Prairie Agricultural Machinery Institute, Humboldt

165


Funding


Further information

– SaskatchewanAgriculture Development Fund;Canada Saskatchewan Agri-Food Innovation Fund

–Gordon HultgreenTel: 306-682-5033Fax: 306-682-5080E-mail: [email protected]


Table 1. Effect of weed clipping on subsequent wild oat andwild mustard density (plants/m ). Mean of four field trialsconducted by PAMI. Fields used as replicates to determineLSD. Assessments done in spring of 2001.

2

166

2000 -

1800 -

1600 -

1400 -

1200 -

1000 -

800 -

600 -

400 -

200 -

0 -

Lent

ilyi

eld

(kg/

ha)

Year1999 2000

Check

Clip - stage 1

Clip - stage 2

Clip - stage 3

Clip - stages 1, 2, 3

Herbicide

Figure 1. Effect of weed clipping on lentil yield -- Scott -- 1999 - 2000.Error bars represent the LSD within years.0. 05

70 -

60 -

50 -

40 -

30 -

20 -

10 -

0 -

Wild

oatd

ensi

ty(p

lant

s/sq

.met

re)

Year of clipping/year of assessment1999/00 2000/01

Check

Clip - stage 1

Clip - stage 2

Clip - stage 3


Herbicide

Figure 2. Effect of weed clipping on subsequent wild oat density-- Scott -- 1999 - 2000. Error bars represent LSD within years.0. 05

40 -

35 -

30 -

25 -

20 -

15 -

10 -

5 -

0 -

Lam

bsqu

arte

rsde

nsity

(pla

nts/

sq.m

etre

)

Year of clipping/year of assessment2000/01

Check

Clip - stage 1

Clip - stage 2

Clip - stage 3


Herbicide

Figure 4. Effect of weed clipping on subsequent lambsquarters density -- Scott -- 1999 - 2000.Error bar represents LSD .0. 05

1400 -

1200 -

1000 -

800 -

600 -

400 -

200 -

0 -Wild

mus

tard

dens

ity(p

lant

s/sq

.met

re)

Year of clipping/year of assessment1999/00 2000/01

Check

Clip - stage 1

Clip - stage 2

Clip - stage 3


Herbicide

Figure 3. Effect of weed clipping on subsequent wild mustard density-- Scott -- 1999 - 2000. Error bars represent LSD within years.0. 05

100 -

90 -

80 -

70 -

60 -

50 -

40 -

30 -

20 -

10 -

0 -

ConclusionsWhile results are preliminary,weed clipping may havepotential as a means ofreducing weed seed returnfollowing a short stature non-competitive crop. Furtherstudy is warranted to defineoptimum timing for clippingand to improve consistencyof results.


UnclippedClipped

LSD0. 05

Wild oat density(plants/m )

2

296

22

Wild mustard density(plants/m )

2

17621

167

from deep levels where lightcould not normally penetrate.Night tillage may also slowweed seeds’ germinationrates, thus allowing a seededcrop a chance to emerge

before weed emergence.Time of season can influencethe success of photocontrolsince many species have

seasonal dormancy periods.A study in southern Swedenfound that night tillage wasmost effective in May, lesseffective in April and August,

and ineffective in October.Reduction in weedemergence from nighttimetillage was quite small in thisstudy, ranging from 5 to 30%.

Success with photocontrolmay be dependent on the typeof tillage implement used.Nighttime tillage waseffective in reducing seedlingemergence when a mold-board plow was used, but wasineffective when a chisel

plow was used. Moldboardplowing may have moved ahigher percentage of deeplyburied, light sensitive weedseeds to the surface than thechisel plow.

Results from photocontrolhave been inconsistent withgermination reductions

ranging from no effect to ashigh as a four-fold decrease

in some cases. In othercases, a decrease in relativeemergence of many annualspecies has been reported butabsolute weed numbers inlight-excluded plots were still

unacceptably high.

1 5 ,2 0

1 9

1 8

1 9

1 9

1 5

1 4 ,1 5

seedling s chance of survival. Lightrequirement can be a signal that theseed is close enough to the soilsurface so it has a high probabilityof successful emergence. The lightstimulus is mediated by asophisticated photoreceptor in plantsknown as phytochrome that isextremely sensitive to fluctuations

in light intensity and light quality.Phytochrome functions at all stagesof the plant's life cycle, acquiringinformation on the lightenvironment, and giving the plantthe capacity to adapt to lightfluctuations.

Studies have shown that excludinglight during tillage can reduce weed

seed germination.Photocontrol has been accomp-lished by tilling at night or coveringthe tillage implement with a light-proof cover. Weed emergence fromlight-induced tillage is the result ofthe light flash experienced duringtillage and not from light that may

reach the seed after emergence.Experiments where tillage wasconducted in the dark and the areacovered with opaque plastic sheetshad similar emergence to plots tilledin the dark and not covered.

Light-excluded tillage has generallycaused a greater reduction in thenumber of dicots emerging, with

less impact on grasses. Emergenceof small seeded broadleaf weedspecies such as lambs quarters,pigweeds, and wild mustard werereduced with night tillage, but therewas no effect on large seeded

broadleaf species like velvetleaf.However, another study found norelationship between seed size and

light-induced germination.

Jensen found that weed emergencefrom daytime tillage was due to anincreased emergence of weed seeds

=

1 2

1 3 ,1 4 ,1 5 ,1 6 ,1 7 ,1 8 ,1 9

1 9

1 5

1 6

2 0

1 6

Problem

Background

Many buried weed species develop a light-dependent stimulus for germination. This ledto the concept of photocontrol, (excluding lightduring tillage), as a potential way to reduceweed seed germination. Much research hasbeen conducted on photocontrol in Europe andSouth America, but very little has been done inwestern Canada. We examined the potential ofphotocontrol in western Canada with anextensive literature review to indicate whetherfurther research is warranted.

The soil contains a massive amount of weedseeds with estimates as high as 137,000 seeds

per square meter. The density andcomposition of the seed bank is very

heterogeneous within a landscape and is

closely linked to the land’s cropping historybut will also be influenced by tillage

practices, soil water, and soil type.

In temperate climates most seeds are dispersed

near the end of the growing season. Springannual weed seeds must avoid germinationbefore entering the winter. Late summergermination is avoided by seeds’ primarydormancy, light induced dormancy, andnormally, low amounts of available water. Asautumn progresses low temperaturesadditionally inhibit germination.

Seeds can become light-dependent for

germination upon burial in the soil. The firstplants to emerge after disturbance of naturalvegetation or perennial cover arise fromdormant seed in the soil rather than from

freshly dispersed seed. Large populations ofviable buried weed seeds were found in soil

that had been in pasture for six years. Soilcultivation produced a large flush ofgermination during the subsequent four weeks.Exhumed seeds had low germination levels inthe dark but a 90-second light flash wasenough to cause germination of a largeproportion of the seeds.

Light stimulus from soil disturbance is an

important evolutionary survival mechanism.Soil disturbance will reduce competition fromestablished plants, thereby improving the

1

2 ,3

4 ,5

6 ,7 5 2

8

9

1 0

11

8

9-22 Photocontrol – tilling in the dark?



168

The inconsistent response tophotocontrol is likely due tothe complexity of the seedgermination process. Inaddition to light, weed seeddormancy can also be brokenby fluctuating soil

temperatures, and soil nitrate

level. Also, some weedseeds can lose their light

dependency over time andthere can be considerablegenetic variation within aweed species in their response

to light.

Weed seed-bank dynamics areaffected by agronomicpractices and environmentaland soil conditions. Tilling inthe dark has shown potentialin some experiments;however, results have beeninconsistent. Organicproducers may want toevaluate this practice on theirown farms; however, theyshould not have highexpectations of success.

2 1

2 2

2 2

2 0

Conclusions

Funding

Review coordination

– Canada-SaskatchewanAgri-Food Innovation Fund


References1

2

3

4

5

6

7

8

9

1 0

Wilson, R.G. 1988. Biology of weedseeds in the soil. In

, eds. M.A. Aliteri and M.Liebman. Boca Raton, FL CRC Press,pp. 25-39.

Benoit, D.L., D.A. Derksen, and B.Panneton. 1992. Innovativeapproaches to seed bank studies.

40: 660-669.

Albrecht, H. and E.M. Forster. 1996.The weed seed bank of soils in alandscape segment in Southern Bavaria– I. Seed content, species compositionand spatial variability. 125:1-10.

Ball, D.A. 1992. Weed seed bankresponse to tillage, herbicides.

40: 654-659.

Albrecht, H. and M. Pilgram. 1997.The weed seed bank of soils in alandscape segment in southern BavariaII. Relation to environmental variablesand to the surface vegetation.

131: 31-43.

Clements, D.R., D.L. Benoit, S.D.Murphy and C.J. Swanton. 1996.Tillage effects on weed seed return andseedbank composition. 44:314-322.

Feldman, S.R., C. Alzugary, P.S.Torres, and P. Lewis. 1997. The effectof different tillage systems on thecomposition of the seedbank.

37: 71-76.

Pons, T.L. 1991. Induction of darkdormancy in seeds: its importance forthe seed bank in the soil.5. 669-675.

Wesson, G. and P.F. Wareing. 1969.The induction of light sensitivity in theweed seeds by burial. 20(63): 414-425.

Sauer, J. and G. Struik. 1964. Apossible ecological relation between soildisturbance, light-flash, and seedgermination. 45(4): 884-886.

Weed Managementin Agroecosystems: EcologicalApproaches

WeedSci.

Vegetario

WeedSci.

PlantEcol.

Weed Sci.

WeedRes.

Funct. Ecol.

J. Exp. Bot.

Ecology

11

1 2

1 3

1 4

1 5

1 6

1 7

1 8

1 9

2 0

2 1

2 2

Wesson, G. and P.F. Wareing. 1969. The role oflight in the germination of naturally occurringpopulations of buried weed seeds. 20(63): 402-413.

Smith, H. and G.C. Whitelam. 1990.Phytochrome, a family of photoreceptors withmultiple physiological roles.13. 695-707.

Hartmann, K.M. and W. Nezadal. 1990.Photocontrol of weeds without herbicides.

77, 158-163.

Ascard, J. 1994. Soil cultivation in darknessreduced weed emergence. 372: 167-177.

Scopel, A.L., C.L. Ballare and S.R. Radosevich.1994. Photostimulation of seed germination duringsoil tillage. 126: 145-152.

Jensen, P.K. 1995. Effect of light environmentduring soil disturbance on germination andemergence pattern of weeds. 127:561-571.

Buhler, D.D. 1997. Effects of tillage and lightenvironment on emergence of 13 annual weeds.

11: 496-501.

Fogelberg, F. 1997. Photocontrol of weeds: theseasonal variation in weed reduction on nighttimecultivation. In:

1997 June 22-26; Poznan, Poland.p. 174.

Botto, J.F., A.L. Scopel, C.L. Ballare, and F.A.Sanchez. 1998. The effect of light during and aftersoil cultivation with different tillage implements onweed seedling emergence. 46: 351-357.

Miilberg, P., L. Andersson, and A. Noronha.1996. Seed germination after short-duration lightexposure: implications for the photo-control ofweeds. 33. 1469-1478.

Thompson, K. and J.P. Grime. 1983. Acomparative study of germination responses todiurnally-fluctuating temperatures.20: 141-156.

Bouwmeester, H.J. and C.M. Karssen. 1989.Environmental factors influencing the expression ofdormancy patterns in weed seeds. 63:113-120.

J. Exp. Bot.

Plant Cell Environ.

Naturwissenchaften

Acta Horticult.

New Phytol.

Ann. Appl. Biol.

Weed Technol.

European Weed Research Society10th Symposium;

Weed Sci.

J. Appl. Ecol.

J. Appl. Ecol.

Ann. Bot.


References

Funding


1

2

3

4

6

7

Foster, K. 1996.FARMFACTS. Organic CropProduction: Weed Management.Sustainable Production Branch,Saskatchewan Agriculture andFood.

Macey, A. 1992. OrganicField Crop Handbook.Canadian Organic Growers Inc.,Ottawa, ON.

Best, K.F. and G.I. McIntryre.1975. The biology of Canadianweeds. 9. L.Can. J. Plant Sci. 55:279-292.

Bibbey, R.O. 1935. Theinfluence of environment uponthe germination of weed seeds.Sci. Agr. 16: 141-150.

Banting, J.D. 1977. Growthhabit and control of wild oats.Canada Agriculture Publication1531 (Revised).

Canada. Experimental Farm,Indian Head, Sask. 1974.Research Summary 1974.

Canada. Experimental Farm,Scott, Sask. 1954. ProgressReport 1948-1953.



Thlaspe arvense

5

Major findingsPre-seeding tillage timing did notalways have an impact on weeddensity or crop yield. When it wasimportant, it was generally better toseed as close to tillage as possible.Pre-seeding tillage timing appearedto have more effect under the highermoisture conditions experienced atMelfort. However, pea yields wereimproved at Scott in 1998 if seedingwas conducted soon after tilling(Table 1). At Melfort, flax yielddeclined as seeding was delayed(Table 1) with field pea and canolayields showing similar trends.Overall yields were low at Melfortin 1999 but flax showed similaryield responses to pre-seedingtillage timing with highest yieldsoccurring when seeding wasconducted within one day of thefinal tillage operation (data notshown with this article).

ConclusionsThere may be yield benefits toseeding soon after the final pre-seeding tillage operation. Whetherthese benefits materialize or notprobably depends on the timing ofmoisture availability for weedgermination prior to seeding crop,and on conditions that permitadequate crop growth.

Problem

Background

Study description

Organic producers often use spring cultivationto stimulate weed populations to germinate.Once weeds have emerged, they can becontrolled before or as the crop is seeded.Seeding is delayed to allow time for weedgermination and tillage. How long should thefarmer wait between final tillage and seedingthe crop?

Spring tillage can be used for weed control aswell as to prepare the seedbed. Shallow pre-seeding tillage (less than three inches) in earlyspring can aerate and warm the soil, thusstimulating weed seedling germination.Harrow-packing following spring cultivationfirms the soil and further encourages weedseed germination. The tillage operation shoulddestroy weed growth while conserving asmuch soil moisture and crop residue as

possible. The second tillage operation is

delayed until weeds have emerged. Seedingcan then be conducted after the second tillageoperation. This practice can be especiallysuccessful at reducing the weed seedbank ofwinter annual and early emerging species, such

as stinkweed, knotweed, Russian pigweed,

Russian thistle, lambs quarters, wild mustard,wild oats, and wild buckwheat. Weed controlcan be very successful with delayed seeding,but the practice may reduce crop yields eitherbecause of increased losses due to delayedharvest, or from reduced moisture in tilled

soils. Seeding should only be delayed longenough to let weeds emerge.

The study was conducted at Scott from 1997 to1999 and at Melfort from 1997 to 2000. Bothgrass and broad-leaved weeds were seeded inthe early spring, and were then cultivated andharrow packed. Field pea, lentil, canola andflax were sown the same day, and one, two,three, four or five days later.

Our experimental design was a randomizedcomplete block with four replications.

1

2

3

4

5 ,6 ,7

9-23 Weed control – false seed bed technique


Days betweentillage andseeding

543210

Flax yieldMelfort, 1998

kg/ha-1

19447978489310321168

Field pea yieldScott, 1998

kg/ha-1

1335.81383.21345.31428.91488.21492.9

Table 1. Delaying seeding after tillage -- effecton field pea and flax yield at Scott and Melfort,respectively -- 1998.

169


170

ConclusionsWeed movement onto farms and among fieldscan be slowed. Importing weeds can bereduced by sowing clean seed, by purchasingonly clean plant material such as hay, and bycleaning equipment traveling among fields.Careful management of non-crop areas canreduce weed movement into fields. Chaffcollection can reduce future weed problems.

References

Funding –

Further information

1

2

3

4

5

6

7

Ashford, R. 1978. Weeds and Their Control.Wascana Institute of Applied Arts and Sciences,Regina, Saskatchewan.

Foster, K. 1996. FARMFACTS. Organic CropProduction: Weed Management. SustainableProduction Branch, Saskatchewan Agriculture andFood.

Marshall, E.J.P. 1989. Distribution patterns ofplants associated with arable field edges. Journal ofApplied Ecology 26: 247-257.

West, T.M., E.J.P. Marshall, and G.M. Arnold.1997. Can sown field boundary strips reduce theingress of aggressive field margin weeds? 1997Proceedings of Brighton Crop ProtectionConference - Weeds.

Anonymous. 1994. Practical Crop Protection.Weeds, Insects, Diseases. Alberta Agriculture Foodand Rural Development Publishing Branch.

Harmon and Klien. 1934. The percentage andviability of weed seeds recovered in the feces offarm animals and their longevity when buried inmanure. J. American Soc. Agron. 26: 762-767.

Lee, H.C. 1995. Non-chemical weed control incereals. Brighton Crop Protection Conference -Weeds. Vol. 3, 11611170.

Canada-Saskatchewan Agri-FoodInnovation Fund


It is often recommended that weedsbe removed along fence lines,shelterbelts, road allowances or inother non-crop areas to prevent themfrom spreading to fields. However,only a few weeds on field marginspose a real threat of spreading into

adjacent fields. Completeelimination of field margin weedsmay damage beneficial insects thatrequire weeds as host species. Ifnon-crop areas are especially weedy,they can be seeded to competitivenative grasses. Movement of Canadathistle into fields is reduced byhaving the field margin sown tonative species, rather than having an

unsown border. If these areas aremowed, delaying operations untillate July will allow ground nesting

birds to raise their broods.

A chaff saver behind the combinecan collect weed seeds. It isespecially good at collecting cropseeds that blow over and causevolunteer problems in followingyears. It is also effective at removinglarge numbers of seeds of latermaturing weeds. This practiceprevents some weed movementwithin a field and provides usefullivestock feed. Weed seeds shouldbe cooked, ground or pelleted beforeusing as feed. Chickens areespecially good at destroying weedseed viability. Sheep, horses, swineand cattle are progressively lesseffective at destroying weed seed

viability. If green feed containsweed seeds, it can be made intosilage to destroy them. Properlycomposting livestock manure should

kill most weed seeds.

3

4

5

6

7

Problem

Background

Weeds enter farms and fieldsin various ways. Historically,most of our weeds wereintroduced from Europe andother areas as a result ofhuman immigration to theprairies. On individual farms,weeds are introduced fromneighbouring farms, fromsuppliers, from road margin tofield and from field to field.How can we prevent newweeds establishing on farms?

Introduction of weeds ontothe farm can be slowed, butnot halted, by carefulprevention and sanitation.Some seed movement isinevitable, due to birds,mammals, movement duringsnow melt, etc.

The first step in preventingweed introduction is to sowclean seed. Weed seeds arefound as contaminants in the

seed from other farms, or inseed cleaned at grain

elevators. Weed seeds andvegetative parts can betransported on equipment. Itis a sound practice tothoroughly clean equipmentthat moves between fields orbeyond weed patches. This isespecially important if customwork is done. A tarp overgrain, soil or feed beingtransported will preventcontamination along roads orin yards.

1

2

9-24 Weeds – how to prevent new problems



Untreated and herbicide(imazamox + imazethapyr50:50 applied at a rate of 30 g

ai/ha ) checks also wereincluded in addition to thefactorial arrangement ofharrow type and passes.Treatments were replicatedfour times. Subsubplots were2 m x 5 m. Data collectedincluded field pea density,total weed density and freshweight, and seed yield.

The tine harrow and moderateand high disturbance settingsof the flex-tine harrow causeda decline in field pea densityas the frequency of harrowingincreased (Figure 2). Theflex-tine harrow’s lowdisturbance setting resulted inminimal crop injury withplant densities similar to theherbicide treatment and theuntreated check.

Highest weed densities wererecorded with the flex-tineharrow at the low disturbancesetting (Table 1). All otherharrow types and settingsresulted in similar weeddensities. Two or moreharrow passes resulted in thelowest weed densities for allthe harrow types and settings.

We found no significantdifference in weed freshweight between harrow typesor disturbance settings (Table2). Although the flex-tineharrow’s low disturbancesetting resulted in the highest

-1

Major findings

Study descriptionThe study was conducted on wheatstubble from 1999-2001 An earlyspring cultivation was performed onthe experimental area. Wild oat andwild mustard were seeded across theplots at a target density of 100

plants/m for each species. Asecond shallow cultivation was doneimmediately after weed seeding touniformly distribute the weed seeds.

Field pea ( Grande) was seeded in

early May at a rate of 220 kg/ha

(80 viable seeds/m ) with a hoe-drillplot seeder (22cm row-space)according to the treatment design.Field pea was inoculated with 5.6

kg/ha of granular inoculant appliedin the seed row. The experimentwas conducted according to arandomized complete block design.

Treatments included a factorialcombination of harrow type (tineand flex tine), levels of flex tine soildisturbance (low, moderate, andhigh), and number of operations(one - four passes). Settings for theflex-tine harrows are illustrated inFigure 1.

Our strategy for multiple harrowpasses was: one pass = singleharrowing at crop’s three to fournode stage; two passes = singleharrowing at crop’s three to fournode stage and a single harrowingone week later; three passes =double harrowing at crop’s three tofour node stage and a singleharrowing one week later; and fourpasses = double harrowing at crops’three to four node stage and adouble harrowing one week later.

.

-2

-1

-2

-1

cv.

Problem

Background

Post-emergence harrowing generally results inlow selectivity, which is the ratio between

weed control and crop injury. Many organicgrowers have suggested that selectivity of post-emergence harrowing could be improved withchanges in implement design.

The flex-tine weeder is a common implementused in Europe by organic growers in crops

such as sugar beets and potatoes. The flex-tine harrow is also referred to as a finger

weeder. The springy tines of the flex-tineharrow are gentle enough not to harm the cropwhile uprooting or covering small weeds. Thelong, thin spring-tines may be pushed aside bya well-established crop, allowing for selectiveweed control between rows. The amount ofsoil disturbance caused by the flex-tine harrowcan be adjusted by adjusting the angle of thetine relative to the soil surface.

Fifty-two percent of organic growers surveyedin Saskatchewan use post-emergence

harrowing as a weed control practice. Thereare very few published papers on post-emergence harrowing in western Canada.Results of a 12-year study at Indian Headshowed that yield of barley and spring wheatgrown under weed-free conditions was notreduced by a single harrow pass conducted at

emergence, the 1.5 or 2.5 leaf stage. Kirklandreported that multiple post-emergenceharrowing passes reduced wild oat panicles andfresh weight in spring wheat in two years outof a three-year study. However, spring wheatyield was improved in only one year of thestudy. Three to four passes were required inorder to obtain a 40 to 80% reduction in wildoat fresh weight.

Studies have shown that field pea can toleratepost-emergence tillage performed with a

harrow or rotary hoe. Yield responses frompost-emergence tillage in field pea have ranged

from 0 to 18%.

1

2

3

4

5 6

7 ,8

8 ,9 ,1 0

This study’sobjectives were to determine if selectivitydiffered between a Lely Flex-tine harrow and atine harrow; and to determine whether multiplepasses will optimize weed control in field pea.

9-25 Field pea harrowing – flex-tine weeder or tine harrow?


171


172

weed densities, maintainingsufficient plant populationsallowed the crop to competemore effectively with weeds.Three or more passes resultedin up to a 40% decline inweed fresh weight (relative tothe untreated check),independent of harrow typeor setting.

All harrow types and settingsresulted in similar field peayields (Table 3). Highestyields were obtained with thethree pass system whichresulted in approximately20% higher crop yield thanthe untreated check.Herbicides improved cropyield by 60%.

Results from this study areconsistent with other studiescomparing harrow types. Atine harrow was moreeffective in reducingbroadleaf weed numbers thana rotary harrow, however it

caused more crop injury.

Rasmuusen reported that aflexible chain harrow was amore efficient weed killerthan a spring-tine harrow butit also caused more cropdamage in field pea andspring wheat. He concludedthat similar results could beobtained with all harrowtypes, if their settings areadjusted to give similar plantcovering effects.

11

1 0

ConclusionsCrop injury could be reduced byusing a low disturbance setting onthe flex-tine harrow. The flex-tineharrow can be easily adjusted tovary the amount of soil disturbanceand crop covering. The harrowshould be set to minimize areduction in plant density. Highlevels of soil disturbance did notresult in improved weed control.The three-pass system employed inthis study resulted in a 50%reduction in weed biomass and a20% increase in field pea yield.

90 -

80 -

70 -

60 -

50 -

40 -

30 -

20 -

10 -

0 -

Fie

ldpe

apl

ants

/m-2

Tine FT low FT mod FT high

One pass

Two passes

Three passes

Four passes

Untreated

Herbicide

Figure 2. Tine harrow, flex-tine harrow setting, and number of post-emergence passes -- effect onfield pea density (plants/m ) -- Scott -- 1999 - 2001.

-2

Moderate

Frame Low

High

50° 85°

Figure 1. Settings for flex-tine harrow

experiment. Scott -- 1999 - 2001.


Table 1. Tine harrow, flex-tine harrow setting, and number ofpost-emergence passes -- effect on weed density(plants/m ). Scott, SK. 1999-2001.

2

FactorHarrow

LSD (P= )

Number of passes

LSD (P= )

Checks

TineFlex-tine - Low disturbanceFlex-tine - Moderate disturbanceFlex-tine - High disturbance

OneTwoThreeFour

UntreatedHerbicide

0. 05

0. 05

Weed density (plants/m )

19

19

2

55936857

85666259

10726

Table 2. Tine harrow, flex-tine harrow setting, and number ofpost-emergence passes -- effect on weed freshweight (g/m ). Scott, SK. 1999-2001.

2

FactorHarrow

LSD (P= )

Number of passes

LSD (P= )

Checks

NS


OneTwoThreeFour

UntreatedHerbicide

* = Differences between means are not significant

0. 05

0. 05

Weed fresh weight (g/m )

NS*

71

2

315375338307

395373271296

44130

References1

2

3

4

5

6

7

8

9

1 0

11

Rasmussen. J. 1990. Selectivity, an importantparameter on establishing the optimum harrowingtechnique for weed control in cereals.Proceeding of the 1990 European Weed ResearchSociety Symposium, Integrated weed managementin cereals. Helsinki, Finland. Pages 197-204.

Ascard, J. and R.R. Bellinder. 1996. Mechanicalin-row cultivation in row-crops. Proceedingsof the Second International Weed ControlCongress, Volume 3. Copenhagen. Pages 1121-1126.

Rasmussen, J. and Svenningsen, T. 1995.Selective weed harrowing in cereals. Biol. Agric.Hort. 12: 29-46.

Beckie, M.A.N. 2000. Zero-tillage and organicfarming in Saskatchewan: An interdicisiplinarystudy of the development of sustainableagriculture. PhD Thesis. University ofSaskatchewan, Saskatoon, SK.

Lafond, G.P. and K.H. Kattler. 1992. Thetolerance of spring wheat and barley to post-emergence harrowing. Can. J. Plant Sci. 72: 1331-1336.


Al-Khatib, K., C. Libbey, and R. Boydston.1997. Weed suppression with greenmanure crops in green pea. Weed Sci. 45: 439-445.

Boerboom, C.M. and F.L. Young. 1995. Effectof postplant tillage and crop density on broadleafweed control in dry pea ( ) and lentil( ). Weed Technol. 9:99-106.

Rasmussen, J. 1993. Yield response models formechanical weed control by harrowing at earlygrowth stages in peas ( L.). WeedRes. 33. 231-240.

Rasmussen, J. 1992. Testing harrows formechanical control of annual weeds in agriculturalcrops. Weed Res. 32: 267-274.

Johnson, E.N. 2001. Mechanical weed controlin field pea. M.Sc. Thesis. University ofSaskatchewan. Saskatoon, SK.

In

In

Brassica

Pisum sativum

Lens culinaris

Pisum sativum

Funding –

Research coordination –

Canada-Saskatchewan Agri-FoodInnovation Fund

Eric JohnsonTel: 306-247-2011 Fax: 306-247-2022

E-mail: [email protected]

173


Table 3. Tine harrow, flex-tine harrow setting, and number ofpost-emergence passes -- effect on field peayield (kg/ha). Scott, SK. 1999-2001.

FactorHarrow

LSD (P= )

Number of passes

LSD (P= )

Checks

NS


OneTwoThreeFour

UntreatedHerbicide

* = Differences between means are not significant

0. 05

0. 05

Field pea yield (kg/ha)

NS*

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