kentucky pest news march 12, 2013

7/29/2019 Kentucky Pest News March 12, 2013

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Online at: www.uky.edu/KPN

Number 1331 March 12, 2013

CORN- Use of Strobilurin Fungicides by Top-Yielding

Corn Producers in 2012

TOBACCO- Managing Rhizoctonia Diseases in

Tobacco Float Systems- Pythium Root Rot in the Float System

FRUIT CROPS- Perennial Canker of Peach

-Spotted Wing Drosophila Management in KY

GREENHOUSE- One weird trick for spider mite control

in the greenhouse

DIAGNOSTIC LABORATORY HIGHLIGHTS

CORN

Use of Strobilurin Fungicides by Top-Yielding

Corn Producers in 2012By Paul Vincelli and Don Hershman, ExtensionPlant Pathologists. Chad Lee, ExtensionAgronomist

Fungicides in the strobilurin class (or “strobi”class) are highly effective products for control of certain important corn diseases. Brand names

such as Headline ®, Quadris ®, Stratego ®, Evito®, Fortix ® and Approach ® contain strobilurinfungicides1. Strobilurin fungicides are excellentfor preventative control of gray leaf spot, northernleaf blight, and southern rust, all of which areconcerns in Kentucky corn production.

According to the 2012 National Corn YieldContest results (report available at:http://www.ncga.com/for-farmers/national-corn-yield-contest), 40% of top-yielding producers

2

1 Note: Strobilurin fungicides include pyraclostrobin (the active ingredient in Headine®), azoxystrobin (thea.i. in Quadris®), trifloxystrobin (one of two a.i.’s inStratego®), fluoxastrobin (the a.i. in Evito® and one of two a.i.’s in Fortix®), picoxystrobin (the a.i. inApproach®), and several other pre-mix fungicides.2 The report provides state-by-state results for anywherefrom one to three growers in each production class. Allof these were included in our count.

used a foliar strobilurin fungicide at least once in their contest-winning field. Of course, of this

also means that 60% of the top-yielding

producers did not apply a foliar fungicide

treatment in their contest-winning field.

If we look at the 2012 Kentucky Yield Contestresults (athttp://www.uky.edu/Ag/GrainCrops/YieldContest/ CornYieldContest/2012CornContest_WinnersProd

uctionSummary.pdf ), we find that only one of nine Kentucky winners used a foliar spray of a

strobilurin fungicide in their contest-winning field .

The above indicates that high-yield corn producerssometimes—though not always—perceive abenefit from applying a strobilurin fungicide inhigh-yield fields. Some of the national winnersreported applying fungicide in order to reducestress on crops, whereas others reported applyingthem for disease control.

Strobilurin fungicides do sometimes promotegrowth and leaf health even in the absence of significant disease pressure, and this cansometimes result in an economic benefit (even avery substantial one). However, these stress-reducing and growth-promoting effects arevariable from field to field and year to year,ranging from a yield loss of 5+ bushels to a 20+

Lexington, KY 40546

http://www.uky.edu/KPN



http://www.ncga.com/for-farmers/national-corn-yield-contest



http://www.uky.edu/Ag/GrainCrops/YieldContest/CornYieldContest/2012CornContest_WinnersProductionSummary.pdf












bushel yield increase. Given that many of thenational winners that applied fungicide farm instates with high humidity, we suspect a substantialnumber of them applied fungicide for reasons of disease control (though we don’t know for sure,since survey data are unavailable).

What does this mean for producers?Strobilurin fungicides are effective sometimes, butcost money when they are not. Disease risk is stillthe best guidance for deciding whether astrobilurin application might provide an economicreturn. Figure 1 provides a summary of diseaserisk factors. The more of these that are in place,the more likely a producer is to see an economicbenefit. For example, it may make sense to applya strobilurin to a bottom field under irrigation, or afield of corn-after-corn under conservation tillage.

Since crop response to strobilurin fungicides canbe so variable, there is no substitute to runningyour own strip trials. Extension agents canprovide guidelines on ways to optimize theinformation you get from a strip trial. Always besure to leave agronomically similar untreatedcontrol strips for comparison.

Figure 1. Decision guide for determining the likelihood of an

economic response to foliar strobilurin fungicide in corn inKentucky. The higher on the list, the more important the

factor.

TOBACCO

Managing Rhizoctonia Diseases in TobaccoFloat SystemsBy Kenny Seebold, Extension Plant Pathologist

Tobacco transplant production is now underwayKentucky, and disease management is probablynot at the top of the list of concerns for manyproducers. We’re very early in the productioncycle and weather conditions have been on thecool side, so for now there’s not much risk to anyof the major diseases that occur on tobaccotransplants. Things will change, though, as wemove into April. Temperatures will rise, and thesewarmer temperatures will bring in increased risk to Rhizoctonia damping-off and, later, target spot.Taking steps early in the transplant season can

help reduce the likelihood of losses to thesediseases before plants go to the field. Thefollowing are suggested practices for managingRhizoctonia damping-off and target spoteffectively. Detailed information about thesediseases can be found in the fact sheet PPFS-AG-T-02, Managing Target Spot and Rhizoctonia

Damping-Off in the Float System, available online at

www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/ppfsagt2.pdf .

Damping-off

Infested soil or Styrofoam trays are the mostcommon sources of R. solani in transplantproduction. Sclerotia and dormant hyphaeassociated with organic debris are the principalresting structures of R. solani. These can be foundeasily on the surfaces of infested trays and incracks and crevices in older Styrofoam trays.Infested trays thus become a source of inoculum insubsequent years if not sanitized properly orreplaced. Using new trays for each crop of transplants will all but eliminate the risk of

carrying over inoculum from previous transplantcycles, but this option can be expensive and maycreate issues with disposal of old trays. Used traysshould be sanitized properly (refer to ID-160, The2013-2014 Kentucky-Tennessee TobaccoProduction Guide, for more information) to reducecarryover of inoculum.

http://www.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/ppfsagt2.pdf







Minimizing leaf and stem wetness should be apriority, and providing adequate ventilation toplants will help keep plants as dry as possible.Properly-timed fungicide applications can beeffective in controlling damping-off. We getreasonable suppression with the mancozeb-based

fungicides Dithane DF, Manzate Pro-Stick, andPenncozeb. These products are applied at a rate of 0.5 lb/100 gallons of finished spray solution (or 1level teaspoon per gallon) once plants havereached the size of a dime. Use 3-5 gallons of thefungicide solution per 1000 square feet, applied asa fine spray (to ensure good coverage) on youngerplants; and increase spray volume to 6-12 gallonson older plants. Begin applications beforesymptoms develop, or immediately after the firstsymptoms are observed at the latest, and continueon a 5-7 day schedule until plants are ready to go

to the field.

Target Spot

As with damping-off, sanitation and good growingpractices are the best defense against target spot.Because nitrogen deficiency can increase thesusceptibility of tobacco seedlings to the targetspot pathogen, maintain nitrogen within therecommended range of 75-125 ppm. This practicewon’t eliminate the risk to target spot but it willreduce the likelihood of a severe outbreak.

Mancozeb fungicides, as described for damping-off, should be applied when conditions favordisease. These products work reasonably wellwhen used in conjunction with sound managementpractices. A better option for target spot in thefloat bed is Quadris fungicide, which received a“Special Local Need”, or ”24 (c)” label for controlof target spot in float beds through December 31,2018. Under the provisions of this label, growerswill be able to make ONE application of Quadrisat a rate of 6 fl oz/A, which is the equivalent of 0.14 fl oz (4 cc, or roughly 1 tsp) of product per

thousand square feet of float bed (roughly 400trays) applied in a recommended volume of 5gallons. This should be adequate to get good leaf coverage and rundown of fungicide solution ontostems. For best control of disease, we recommendmaking the Quadris application before symptomsare seen (or when they first appear at the verylatest) and at a time when the plants would be themost susceptible to target spot. To get ahead of

the disease, a good strategy would be to applyQuadris after the 1st or 2nd clipping. Aftermaking the Quadris treatment, producers shouldswitch back to mancozeb until plants are set in thefield. It is also important to note that the float-bedapplication counts towards the seasonal limit for

Quadris in the field. Following the manufacturer’suse guidelines for Quadris is critical to stay incompliance with the label, and to minimize therisk of the target spot pathogen developingresistance to this important fungicide.

Figure 2. Damping-off, caused by Rhizoctonia solani, on

tobacco seedlings.

Figure 3. Leaf yellowing and necrosis associated with

damping-off on tobacco transplants.



Figure 4. Target spot on tobacco transplants. Lesions have

the characteristic zonate (concentric rings) pattern of

growth on affected leaves.

Pythium Root Rot in the Float SystemBy Kenny Seebold, Extension Plant Pathologist

Pythium root rot (PRR) is the most importantdisease of tobacco seedlings grown in float beds.Plants can be affected by PRR from the momentthat seed germinate until seedlings are set in thefield; however, the disease is found mostcommonly after the middle of April in most years.This is generally when water temperatures in floatbeds begin to climb above 70 °F, favoring rapiddevelopment of the species of Pythium that causePRR in float systems. Pythium root rot has beenfound early in the production cycle, though, whentemperatures have been above-normal in March.If left unmanaged, PRR can cause a significantloss of useable transplants. When seedlings withPRR are transplanted, they are more likely todamp-off than healthy plants and are moresusceptible to diseases like Fusarium wilt andblack shank. Fortunately, this disease can bemanaged effectively with good growing practices

and fungicides.

Prevention is the most effective management stepfor PRR, and sound sanitation is the keypreventive practice that should be employed forthis disease. When seeding, use new trays or thosethat have been disinfested with a 10% bleachsolution to reduce the potential of introduction of

the pathogen. Never use pond or surface water tofill float beds, since water from these sources islikely contaminated with Pythium and other plantpathogens such as Phytophthora or Fusarium.Make sure that shoes and tools are cleaned beforebringing them into a transplant facility, and be

careful to not introduce field soil into float bays.Pythium is a plant pathogen common to most (if not all) Kentucky soils and even small amounts of dirt that make their way into float water can leadto serious outbreaks of disease.

Preventive use of Terramaster 4EC is an effectivemanagement practice for PRR. For prevention of disease, apply 1 fl oz of product per 100 gallons of float water beginning 2-3 weeks after seeding, orwhen roots first enter the water. Additionaltreatments can be made at 2-3 week intervals. Do

not exceed 3.8 fl oz per 100 gallons of water percrop of seedlings, and do not apply Terramasterlater than 5 days before transplanting. Make surethat the product is mixed thoroughly in float baysto minimize the risk of plant injury. “Rescue”applications of Terramaster (1.4 fl oz/100 gallonsof float water) in systems with active PRR willhalt further development of disease andsymptomatic seedlings will likely recover.However, the higher rates of Terramaster used inrescue treatments increase the risk of plant injury.Recuperating plants may still harbor Pythium and

increase their susceptibility to black shank andFusarium wilt. For these reasons, preventive useof Terramaster is recommended over curativeapplications of the product. Before usingTerramaster, or any pesticide, refer to the label forspecific instructions and safety information.Detailed information on this fungicide can befound in the product label, or refer to ID-160(2013-13 Kentucky-Tennessee TobaccoProduction Guide) or PPFS-AG-T-8 (2013Fungicide Guide for Burley and Dark Tobacco).Please note that Terramaster is the only product

labeled for controlling Pythium root rot on tobaccoseedlings grown in float beds. Other products,such as Banrot or Ridomil Gold SL, are notapproved for this use.

Symptom recognition also plays an important rolein managing PRR with fungicides. Rescuetreatments with Terramaster will be most effectiveif treatments are made as soon as symptoms



appear than when a significant level of disease ispresent. The first symptoms of the disease thatmost producers notice are yellowing and stuntingof transplants in well-defined areas of a float bay.Damping-off, or seedling death, can occur insevere cases. During the outbreak, seedlings wilt

and root systems decay to some degree and thiswill be evident even before wilting and yellow isseen on the plants themselves. Roots andsometimes lower stems of plants affected byPythium root rot take on a darkened, necrotic,sometimes slimy appearance. Infected roots willeventually slough off and some re-growth may beobserved; however, new tissue will showsymptoms of PRR within 7-10 days of itsemergence. Consult “Pythium Root Rot inTobacco Float Systems” (University of Kentuckyfact sheet PPFS-AG-T-01) for additional

information on diagnosing and managing PRR.This publication is available atwww.ca.uky.edu/agcollege/plantpathology/ext_files/PPFShtml/ppfsagt1.pdf .

Figure 5. Stunting, yellowing, and damping-off associated

with Pythium root rot in tobacco float beds.

Figure 6. Decay (necrosis) of water roots is a typical

symptom of Pythium root rot on tobacco seedlings, and can

be seen often before plants begin to wilt or turn yellow.

Figure 7. Pythium root rot will progress from water roots to

plug roots if not managed, resulting in extensive decay and

eventual stunting or death of plants.

FRUIT CROPS

Perennial Canker of PeachBy Nicole Ward, Extension Plant Pathologist

Perennial canker of peach is a fungal infection of fruiting twigs, scaffold limbs, or trunks (Figs 8 &9). The disease may also be referred to asCytospora canker, Leucostoma canker, perennialcanker, valsa canker, or peach canker. A commonsymptom is oozing gum from canker sites, sosymptoms may also be referred to as gummosis(Fig 8).

The causal fungi, Leucostoma spp., are weak pathogens that infect stressed or wounded plants.Infections cause cankers, or stem lesions, thatenlarge every year, creating annual rings or target-like growths. These cankers expand until limbsbecome girdled and die. Cankers often oozegummy sap (gummosis) that eventually hardens(Fig 9).

Gummosis can also be caused by other plantinjuries such as bacterial infection (bacterialcanker of peach), boring or sucking insects, andmechanical damage. It is important to properlydiagnose the cause of gummosis beforeconsidering management options.








The fungi that cause peach canker produce sporesduring spring. Fungal spores ooze from cankersduring cool rainy weather. Consequently, diseaseis often more severe during rainy years.

Prevention of peach canker begins with vigorous

plants and proper orchard sanitation.

• Retain plant vigor. Maintain soilmoisture, fertilize according to soil tests,and mulch properly.

• Avoid plant wounds such as mowerdamage, sunscald, winter injury, andinsect injury.

• Make clean, sharp pruning cuts that healquickly. Avoid jagged cuts.

• Prune peach trees during late winter,preferably during late-February or March.

• Prune during dry weather only. Fungalspores spread during wet conditions.

• Maintain a clean orchard by pruning deadand damaged wood. Remove cuttingsfrom the orchard; bury, burn, or movethem at least 100 yards from peachplantings.

• Some peach cultivars are less susceptibleto peach canker than others. Use resistantor tolerant trees when possible.

If peach canker becomes a problem in the orchard,a strict sanitation should be implemented. Thereare no fungicide treatments available formanagement of peach canker.

• Remove diseased twigs and limbs, makingclean cuts at least 6 inches below cankers.Remove diseased cuttings from theorchard.

• Infected trunks may require “surgery.”Using a knife or chisel, remove bark atleast one inch around each disease lesion.There is no need to cut into hardwood. Donot paint affected area with wounddressing, paint, or oil.

• Prune during dry weather, only.

• Disinfest pruners and tools between cutsusing a commercial sanitizer, 10% bleach,or 10% Lysol® concentrated disinfectant.

• Apply fungicides to open pruning woundsas a preventative. Captan, iprodione

(Rovral), and thiophanate-methyl (TopsinM) may be applied after pruning (delayeddormant phase), after petal fall, and aftershuck split to prevent new infections.

Sanitation and increased plant vigor are the

primary disease management options for peachcanker. Growers should be aware of potentialrisks for infection and prevent disease outbreaksby following the guidelines above. Once treesbecome infected, the pathogen can spread throughorchards in just a few years. Fungicides do notcure peach canker, and cultural practices are theprimary means for disease management.

Figure 8. Perennial canker of peach limb, advanced

symptoms with oozing sap. (Photo Penn State)

Figure 9. Infection of peach twigs, early symptoms. (Photo

West Virginia University)



Spotted Wing Drosophila Management in KY

By Ric Bessin and Patty Lucas

Spotted wing Drosophila (SWD) was detected intwo locations and confirmed by the USDA APHISthis past fall. This puts Kentucky on the long list

of states where this insect has become a veryserious invasive pest. SWD was first identified inCalifornia in 2008 and has since spread to manystates on the west and east coasts and central stateswhere it is a pest of small fruit crops and other softskinned fruits. I’ve gleaned the information in thisarticle from a number of extension resourcesaround the country in order to provide our ‘best’management recommendations for 2013.

While SWD was found in apple cider vinegar trapsthat were put out in Daviess and Warren Counties,

a commercial grower in Larue County alsoreported having maggots in raspberries that werefrozen this past summer for use in processing. It isvery possible and likely that this insect is also inother counties in Kentucky: at this point we don’tknow. We will be conducting a survey in strategiclocations throughout the state and have receivedsupport from the Kentucky Horticulture Societyfor this effort.

SWD attacks a number of different fruiting cropsand weeds, notably raspberries, blackberries,

blueberries, and strawberries. In 2010 it causedover $300 million in losses to west coaststrawberries alone. What makes this fruit fly aproblem is the ovipositor (egg layer) which ispointed and can penetrate into otherwiseundamaged fruit. Fruit become vulnerable duringthe ripening process as they begin to soften andturn color. So management and the possible needfor insecticide sprays occur just before and duringharvest.

Figure 10. A SWD male with the characteristic wing spots.

An apple cider-baited trap is used to monitor forthis insect in commercial plantings. If no SWDare found then sprays targeting SWD during theharvest period are not recommended. If SWD isdetected then weekly insecticide sprays during thisperiod will help to reduce losses. The trap is made

of a one-quart deli container with a half cup of apple cider vinegar. Sixteen ¼ inch holes arepunched below the rim to allow the SWD to enterand traps are checked weekly, and vinegar ischanged weekly. The trap is reported to work more effectively when placed in a dense part of the plants with shade. This trap will capture alarge number of fly species and severalunimportant fruit fly species. It is critical toidentify the collected specimens carefully with apowerful hand lens or dissecting microscope. Themale SWD are recognized by the single black spot

on each wing and the two dark combs on the frontlegs. The females are recognized by theirovipositor which is hardened and pointed.

To sample fruit for SWD larvae a simple floatationmethod can be used. Place a small number of ripe,apparently undamaged fruit into a gallon bag. Addsugar syrup (mixture of ½ cup sugar mixed into 1quart of water) to the bag and seal the bag. Mashthe berries, then let the berries settle to the bottomof the bag, any small, white larvae present shouldfloat to the top.

SWD Management for Commercial Plantings

• Monitoring plantings with apple cidervinegar traps in the three weeks leading upto harvest.

• Reduce alternate host plants (wildbrambles, poke, nightshade, wildmulberry) in surrounding habitat if practical

• If spotted wing drosophila is NOT found,DO NOT use SWD insecticides before or

during harvest• If SWD IS found, treat crop on 5 to 7 day

intervals as fruit begin to color and softenthrough the end of harvest with arecommended insecticide

• Know and obey pre harvest intervals(PHI) for each insecticide you use verycarefully. Small fruit crops are not



normally treated with insecticides duringthe harvest period

• Rotate among insecticide chemistries forresistance management

• When on a spray program for SWD,continue to monitor with traps and fruit

sampling to determine effectiveness• Use clean harvest to collect and remove

spoiled, damaged, and fallen fruit from theplanting on a regular basis. Bag or buryunwanted fruit to reduce SWD flypopulations.

• Consider a postharvest clean-up spray toreduce the SWD population

Insecticides available for SWD in commercialsmall fruit (insecticides must be used to preventinfestations with SWD) plantings are listed in ID-

94. Some insecticides used during the harvestperiod may result in noticeable residues or odorson harvested fruit.

GREENHOUSE

One Weird Trick for Spider Mite Control in

the GreenhouseBy Jen White, Extension Entomologist forgreenhouse pest control, University of Kentucky

I don’t know about all of you, but I’m heartilytired of seeing flashing ads on every webpage,promoting “One weird trick” or “One strange tip”to prevent aging, to lose weight, etc.However…I actually have a “trick” that I’ve heard about forbiological control of spider mites in thegreenhouse that I’d like to pass along.

Figure 11

These tiny mites (~0.01 inches) are a particularlypersistent problem, because they can remaindormant in cracks and crevices in your greenhouseover the winter. If you had issues with spidermites last season, there’s a very good chancethey’ll be back as soon as you warm your

greenhouse up.

What you can do, after giving your greenhouse asgood a scrubbing as you can, is to strategicallyplace some bush beans in your greenhouse. Putthe beans out before your crop, in areas where youpreviously had spider mite infections, near walls,and near the legs of the benches. Leave the beansin place throughout the season.

Spider mites love bush beans, and will be attractedto the beans. You can use the beans as monitoring

plants, and concentrate your scouting efforts onthese plants. Check them regularly for thepresence of spider mites using a hand lens. Onceyou find spider mites, your next step depends onyour preferred control methods.

Figure 12

For biological control, purchase some predatory(“good guy”) mites, such as Phytoseiulus

persimilis, from a biological control supplier

(http://www.ca.uky.edu/entomology/entfacts/ef125.asp). Distribute the predatory mites on the

bush beans. The beans will now act as insectaryplants for the predatory mites, providing apopulation of spider mites for the predators to eat,and a home base from which the predators canrove out into your crop to destroy spider mitesbefore they reach damaging numbers. As long asyou’ve got a good population of predators on thebeans, you can move the bean plants (or infestedleaves from the plants) around the greenhouse to

http://www.ca.uky.edu/entomology/entfacts/ef125.asp








any spider mite hotspots that you might find overthe course of the season.If biological control is not your style, you can stilluse the bean plants to concentrate the spider mitepopulations away from your crop as a trap plant.Once the spider mite population starts getting high

on the beans, you need to discard the bean plants(FAR away from your greenhouse!) so that thebeans don’t become a source of spider miteinfestation for your crop. You can keep replacingfresh bean plants throughout the season, and maybe able to avoid costly chemical treatment. Keepan eye on crop plants near the beans, and if theystart building up spider mite populations, then youmay need to treat.

A few important points to keep in mind:

1) If you try the predatory mites, monitor thebeans with a hand lens to make sure theyhave BOTH spider mites and thepredatory mites on them. If you just seespider mites without predators, you mightneed to get more predators, or try analternative control tactic.

2) In general, predators are more susceptibleto chemicals than pests. If you need toapply an insecticide or miticide (even for adifferent pest), you might lose your

predatory mites as well. Consider movingthe bean plants out of the greenhouse forthe duration of the treatment, then bringthe beans back in if they’ve got goodpredator populations.

3) The bush bean trick has primarily beendeveloped for tomato crops

(http://www.appliedbio-nomics.com/crop-recommendations/tomato), but should

work for any crop that spider mites likeless than they like bush beans. If they likeyour crop better than bush beans, then thebeans won’t be particularly helpful aseither monitoring, insectary plant or trapplants, although it won’t hurt anything tohave them there. So, for the price of a fewbeans, it’s worth a try!

DIAGNOSTIC LAB HIGHLIGHTS

By Julie Beale and Brenda Kennedy

Late winter agronomic samples seen in the PDDLhave included Sclerotinia crown rot on alfalfa andcold injury on wheat.

On fruits and vegetables, we have diagnosedseveral samples of Phytophthora root rot onblueberry; Phytophthora collar rot on apple;perennial canker ( Leucostoma) on peach; chillinginjury with secondary rots on stored sweetpotato.We have seen quite a few samples of high tunneland greenhouse tomatoes with diagnoses rangingfrom high soluble salts, injury from both high andlow temperature extremes, russet mite infestation,

root knot nematode and tomato spotted wilt virus.

On ornamentals and turf, we have seen greenhousesamples of gerbera with high soluble salts;geranium with cold injury; and ranunculus withblack root rot. Landscape samples have includedwhite pine root decline (Verticicladiella); winterdrying injury on boxwood, holly and cherrylaurel;and pink snow mold on perennial ryegrass (sportsturf).

Note: Trade names are used to simplify the information

presented in this newsletter. No endorsement by the

Cooperative Extension Service is intended, nor is

criticism implied of similar products that are not

named.

http://www.appliedbio-nomics.com/crop-recommendations/tomato








kentucky pest news march 12, 2013

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