Characteristics of WeedsCharacteristics of Weeds•• ““Think dynamic with the ability to make Think dynamic with the ability to make

serious changesserious changes””•• The next few slides will detail some The next few slides will detail some

methods of classifying weeds, strategies methods of classifying weeds, strategies for success and how/why weeds are for success and how/why weeds are weedsweeds

Worst weeds grouped by plant familyWorst weeds grouped by plant family

4444GramineaeGramineae3232CompositaeCompositae

# Species# SpeciesFamilyFamily

1212CyperaceaeCyperaceae77AmaranthaceaeAmaranthaceae77CruciferaeCruciferae

44ChenopodiaceaeChenopodiaceae55EuphorbiaceaeEuphorbiaceae55ConvolvulaceaeConvolvulaceae66LeguminosaeLeguminosae

Adapted from Holm et al 1977; Adapted from Holm et al 1977; ““WorldWorld’’s Worst Weedss Worst Weeds””

WorldWorld’’s Worst Weeds by Rankings Worst Weeds by Ranking

4444purple purple nutsedgenutsedge ((CyperusCyperus rotundusrotundus))3232bermudagrassbermudagrass ((CynodonCynodon dactylondactylon)**)**

Ranking*Ranking*Weed Weed

1212barnyardgrassbarnyardgrass ((EchinochloaEchinochloa cruscrus--galligalli)**)**77junglericejunglerice ((EchinochloaEchinochloa colonacolona)**)**77goosegrassgoosegrass ((EleusineEleusine indicaindica)** )**

55water hyacinth (water hyacinth (EichhorniaEichhornia crassipescrassipes))55cogongrass (cogongrass (ImperataImperata cylindricacylindrica)** )** 66johnsongrassjohnsongrass ((Sorghum Sorghum halepensehalepense)**)**

*Adapted from Holm et al 1977; *Adapted from Holm et al 1977; ““WorldWorld’’s Worst Weedss Worst Weeds””** notice how 6 of the top 8 are grasses** notice how 6 of the top 8 are grasses

Classification of WeedsClassification of Weeds•• Of the 250,000Of the 250,000++ known plant species, 1% known plant species, 1%

(2,500) are considered weedy(2,500) are considered weedy•• Weeds classified by:Weeds classified by:

–– Life cycleLife cycle–– HabitatHabitat–– MorphologyMorphology–– PhysiologyPhysiology

•• These classification schemes will be These classification schemes will be outlined in the next few slidesoutlined in the next few slides

Life Cycle Life Cycle -- AnnualsAnnuals•• Annuals (germinate from seed, grow Annuals (germinate from seed, grow

vegetativelyvegetatively and set seed in one growing and set seed in one growing season)season)–– In Florida we have two distinct types of annual In Florida we have two distinct types of annual

weedsweeds–– Summer annualsSummer annuals: germinate in spring, grow : germinate in spring, grow

vegetativelyvegetatively in summer, flower and set seed in summer, flower and set seed in late summer/early fallin late summer/early fall

–– Winter annualsWinter annuals: germinate in fall, grow : germinate in fall, grow vegetativelyvegetatively in winter, flower and set seed in in winter, flower and set seed in late winter/early springlate winter/early spring

Summer Annual Summer Annual -- SicklepodSicklepod

Cotyledons at seedling Cotyledons at seedling stage stage –– April/MayApril/May Flowering and seed set Flowering and seed set

–– August/SeptemberAugust/September

Summer Annual Summer Annual -- CrabgrassCrabgrass

Cotyledons at seedling Cotyledons at seedling stage stage –– April/MayApril/May Flowering and seed set Flowering and seed set

–– June until frostJune until frost

Winter Annual Winter Annual –– AnnualAnnual bluegrassbluegrass

•• SeedheadSeedhead formation occurs throughout the formation occurs throughout the winter months in Floridawinter months in Florida

Common ChickweedCommon Chickweed

•• Cooler Cooler temperatures temperatures initiate seed initiate seed germination, grows germination, grows throughout the throughout the winter monthswinter months

Life Cycle Life Cycle -- BiennialsBiennials•• Biennials Biennials –– germinate from seed late in germinate from seed late in

one season, grow one season, grow vegetativelyvegetatively, , overwinteroverwinter(resting period), and flower/set seed the (resting period), and flower/set seed the next spring or summernext spring or summer

•• Some biennials will behave like winter Some biennials will behave like winter annuals in Floridaannuals in Florida

Curly DockCurly Dock

Germinates from seed, forms rosette of leaves during the late Germinates from seed, forms rosette of leaves during the late summer and winter months (above left). Long days in the spring summer and winter months (above left). Long days in the spring trigger stem elongation and flower production occurs on the trigger stem elongation and flower production occurs on the elongated stem (above right).elongated stem (above right).

Life Cycle Life Cycle -- PerennialsPerennials•• Perennials Perennials –– persist over multiple growing persist over multiple growing

seasons through vegetative structuresseasons through vegetative structures–– Simple perennials Simple perennials

•• resproutresprout from crown/taprootfrom crown/taproot

–– Creeping perennials Creeping perennials •• reproduce from specialized structuresreproduce from specialized structures

–– Woody perennialsWoody perennials•• reproduce from woody tissuesreproduce from woody tissues

Simple Perennial Simple Perennial -- DandelionDandelion

Creeping Perennial Creeping Perennial bermudagrassbermudagrass

Notice the tough underground rhizomesNotice the tough underground rhizomes

Creeping PerennialCreeping Perennialpurple purple nutsedgenutsedge

Notice the rhizomes and strings of tubers in chainsNotice the rhizomes and strings of tubers in chains

Woody PerennialWoody PerennialSmilax (Greenbrier)Smilax (Greenbrier)

•• Underground corms Underground corms of smilax. Notice how of smilax. Notice how several corms do not several corms do not possess an possess an aboveground sprout. aboveground sprout. This is critical to longThis is critical to long--term survival.term survival.

Woody PerennialWoody Perennialmelaleucamelaleuca

Classifying Weeds by HabitatClassifying Weeds by Habitat

•• Could be anything Could be anything –––– Weeds of corn, weeds of agronomic cropsWeeds of corn, weeds of agronomic crops–– Residential weeds, forestry weedsResidential weeds, forestry weeds–– Aquatic vs. terrestrial weedsAquatic vs. terrestrial weeds–– Disturbed vs. nonDisturbed vs. non--disturbed environmentsdisturbed environments

•• Environmental Protection Agency (EPA) Environmental Protection Agency (EPA) considers site and/or crop to be the considers site and/or crop to be the defining factors in pesticide registrationdefining factors in pesticide registration

Classifying Weeds by MorphologyClassifying Weeds by Morphology

•• This method uses the physical characteristics of This method uses the physical characteristics of the plant to place into separate groupsthe plant to place into separate groups–– DicotsDicots vs. monocotsvs. monocots–– Grasses vs. broadleavesGrasses vs. broadleaves–– Erect growing vs. prostrateErect growing vs. prostrate–– ViningVining, creeping, bunch type, creeping, bunch type–– Large seeded vs. small seededLarge seeded vs. small seeded

•• This is the most commonly used method This is the most commonly used method –– this this will be used to study weeds later in labwill be used to study weeds later in lab

Classifying Weeds by PhysiologyClassifying Weeds by Physiology

•• This method is rarely used and This method is rarely used and distinguishes weeds by the type of distinguishes weeds by the type of photosynthesisphotosynthesis

•• C3 vs. C4 photosynthetic mechanismsC3 vs. C4 photosynthetic mechanisms•• CAM photosynthesisCAM photosynthesis

–– http://www.colorado.edu/eeb/courses/4140bohttp://www.colorado.edu/eeb/courses/4140bowman/lectures/4140wman/lectures/4140--06.html06.html

•• Provides a good overview of these Provides a good overview of these mechanisms mechanisms

Why are weeds successful?Why are weeds successful?StrategiesStrategies (begin and end with the seed)(begin and end with the seed)1.1. Seed germination over a wide range of Seed germination over a wide range of

environmental conditionsenvironmental conditions2.2. Discontinuous germination (dormancy)Discontinuous germination (dormancy)**3.3. Rapid growth rateRapid growth rate4.4. Tremendous seed/Tremendous seed/propagulepropagule productionproduction5.5. Self compatible, but able to outcrossSelf compatible, but able to outcross6.6. Short and long distance dispersalShort and long distance dispersal7.7. LongLong--term survivability, persistenceterm survivability, persistence

* Dormancy will be covered in forthcoming slides * Dormancy will be covered in forthcoming slides on weed biologyon weed biology

Genetics Genetics –– Inherent VariabilityInherent Variability

•• From an ecological standpoint, weeds are From an ecological standpoint, weeds are primary invaders into an open nicheprimary invaders into an open niche

•• Considered general purpose genotypes, Considered general purpose genotypes, plasticity allows for maximum adaptation plasticity allows for maximum adaptation (changes in growth in response to (changes in growth in response to changes in environmental conditions)changes in environmental conditions)

•• Most crops were once weeds, over the Most crops were once weeds, over the years have an artificially streamlined years have an artificially streamlined genetic base (through human selection)genetic base (through human selection)

Ecological Survival StrategiesEcological Survival Strategies

““rr--strategystrategy”” –– large number of offspring with large number of offspring with high dispersion potential high dispersion potential

1.1. smallsmall--seeded annuals such as crabgrass, seeded annuals such as crabgrass, pigweeds, pigweeds, chamberbitterchamberbitter, oxalis, oxalis

2.2. Pioneering species that get into an area and Pioneering species that get into an area and exploit it as much as possibleexploit it as much as possible

3.3. Generally self compatible (able to self cross)Generally self compatible (able to self cross)4.4. Divert tremendous amount of resources into Divert tremendous amount of resources into

reproductive developmentreproductive development

Ecological Survival StrategiesEcological Survival Strategies““kk--strategy annualsstrategy annuals”” –– larger seeded specieslarger seeded species**

•• Lower dispersal rate but still a strong ability to Lower dispersal rate but still a strong ability to exploit an areaexploit an area

•• Divert an equal amount of resources into Divert an equal amount of resources into reproductive development, but fewer, larger reproductive development, but fewer, larger seedsseeds

•• Examples include: Examples include: morningglorymorningglory, cocklebur, , cocklebur, sicklepodsicklepod

•• Most crop plants fit in this category Most crop plants fit in this category –– corn, corn, soybean, peanut, tomatosoybean, peanut, tomato

* * Becoming the problem weeds over the last 10Becoming the problem weeds over the last 10--20 years, 20 years, more difficult to controlmore difficult to control

Ecological Survival StrategiesEcological Survival Strategies

““kk--strategy perennials strategy perennials ––1.1. Maintain high levels of sexual and Maintain high levels of sexual and

vegetative reproductionvegetative reproduction2.2. Divert more resources into vegetative Divert more resources into vegetative

propagulespropagules than seedsthan seeds3.3. Vegetative ability allows for maintained Vegetative ability allows for maintained

persistence in a given areapersistence in a given area4.4. Examples include Examples include hydrillahydrilla, , nutsedgenutsedge, ,

bermudagrassbermudagrass, , torpedograsstorpedograss

Ecological Survival StrategiesEcological Survival Strategies

““kk--strategystrategy”” –– woody perennialswoody perennials1.1. High degree of resources diverted to woody High degree of resources diverted to woody

and other persistence type structuresand other persistence type structures2.2. Slow growth, but generally not outSlow growth, but generally not out--competedcompeted3.3. A reduced degree of sexual reproductionA reduced degree of sexual reproduction4.4. Generally considered climax speciesGenerally considered climax species

Ecological Survival StrategiesEcological Survival Strategies•• The strategies discussed in the previous slides are The strategies discussed in the previous slides are

ecological models of how certain species fit into an ecological models of how certain species fit into an overall ecosystem. Generally in an open niche, roverall ecosystem. Generally in an open niche, r--strategy strategy plants colonize first, followed by kplants colonize first, followed by k--strategy annuals, strategy annuals, perennials and finally woody perennial trees that form perennials and finally woody perennial trees that form climax vegetation. The type of agriculture production or climax vegetation. The type of agriculture production or native ecosystem will dictate the types of weedy species native ecosystem will dictate the types of weedy species that will be a problem. In annual row crop production that will be a problem. In annual row crop production (such as corn, soybean), r(such as corn, soybean), r--annual weeds are problem; annual weeds are problem; as minimum tillage increased, a shift in weeds to kas minimum tillage increased, a shift in weeds to k--annuals was observed, accompanied by an increase in annuals was observed, accompanied by an increase in kk--perennials. In natural areas, woody perennials are perennials. In natural areas, woody perennials are often the major problem (often the major problem (melaleucamelaleuca, climbing fern)., climbing fern).

Dissemination*Dissemination*•• NaturalNatural

–– Wind Wind –– light weight, light weight, pappuspappus, winged, winged–– Flowing water Flowing water –– almost any seed, corky, almost any seed, corky,

irrigation water, aquatic weedsirrigation water, aquatic weeds–– Animals (wildlife) Animals (wildlife) –– hooks, barbs, hooks, barbs,

mucilaginous, excretion (feces)mucilaginous, excretion (feces)–– Forceful dehiscence Forceful dehiscence –– some legumes, oxalissome legumes, oxalis

*most of the spread is via the seed and this changes as a *most of the spread is via the seed and this changes as a function of seed typefunction of seed type

DisseminationDissemination•• Artificial*Artificial*

–– Planting contaminated crop seed, primary Planting contaminated crop seed, primary means of spread and reason for certificationmeans of spread and reason for certification

–– Livestock manure, tropical soda apple spreadLivestock manure, tropical soda apple spread–– Equipment Equipment –– mowers, harvesters, haymowers, harvesters, hay–– Humans Humans –– pant cuffs, shoes, clothingpant cuffs, shoes, clothing–– Ballasts of ships, packing crates, nursery, Ballasts of ships, packing crates, nursery,

water craft, trailerswater craft, trailers–– Introduction as a potential crop or ornamental Introduction as a potential crop or ornamental

* Spread via humans, long range spread is mainly through * Spread via humans, long range spread is mainly through human movement and activitieshuman movement and activities

Concepts to UnderstandConcepts to Understand•• The major weed problems worldwide with The major weed problems worldwide with

most being grassesmost being grasses•• How weeds are classifiedHow weeds are classified•• Strategies weeds have to be successful, Strategies weeds have to be successful,

including geneticsincluding genetics•• Ecological aspects of weedsEcological aspects of weeds•• Dissemination characteristicsDissemination characteristics