Weed Biology and Management

Curtis RainboltCurtis Rainbolt

Extension Weed Extension Weed ScientistScientist

Everglades RECEverglades REC

Weed Biology and its Impact on Management

What makes a plant a weed?What makes a plant a weed? Cost of weedsCost of weeds Why do weeds always win? BiologyWhy do weeds always win? Biology

Get to know the enemyGet to know the enemy Anatomy of a weedAnatomy of a weed Common south Florida weedsCommon south Florida weeds

Strategies for weed managementStrategies for weed management

Definition of a weed:Definition of a weed:

A weed is an A weed is an undesired plant out undesired plant out of placeof place Water hyacinth in a Water hyacinth in a

aquatic garden: not aquatic garden: not a weeda weed

Water hyacinth Water hyacinth clogging canals: a clogging canals: a weedweed

Weed impactsWeed impacts

Weeds are costlyWeeds are costly $24 billion in $24 billion in

agricultural crop agricultural crop lossloss

$3 billion in $3 billion in control costscontrol costs

Pimentel et al. 1999

Weeds are costlyWeeds are costly

It is estimated that It is estimated that without control, without control, sugarcane losses would sugarcane losses would be 50% from heavy be 50% from heavy infestations of fall infestations of fall panicumpanicum

In 2000, over $51 In 2000, over $51 million was spent for million was spent for weed control in US weed control in US sugarcanesugarcane

Why do weeds always win?Why do weeds always win?

Dormancy: broken when conditions Dormancy: broken when conditions favor survivalfavor survival

Rapid early growth and expansionRapid early growth and expansion Early and fast root growth Early and fast root growth Efficient uptake and processing of Efficient uptake and processing of

nutrients and waternutrients and water

Ability to reproduce early in life cycleAbility to reproduce early in life cycle Prolific seed productionProlific seed production Absorb resources in excessAbsorb resources in excess Tolerate low levels of resourcesTolerate low levels of resources Genetic and environmental adaptabilityGenetic and environmental adaptability Ability to develop resistance to control Ability to develop resistance to control

measuresmeasures

Why do weeds always win?Why do weeds always win?

Reproduction by seedReproduction by seed First infestation is dependant on seedFirst infestation is dependant on seed

Estimates of the total number of weed seeds in the soil range Estimates of the total number of weed seeds in the soil range from 4 million to 133 million per acre furrow slicefrom 4 million to 133 million per acre furrow slice

Vegetative reproductionVegetative reproduction Less longevity in soil than seedsLess longevity in soil than seeds Very small structures can reproduceVery small structures can reproduce

Canada thistle: ¼” piece of root results Canada thistle: ¼” piece of root results in new plantin new plant

Torpedograss can reproduce from very Torpedograss can reproduce from very small segments of rhizomessmall segments of rhizomes

Can be as prolific as seed productionCan be as prolific as seed production Yellow nutsedge: 1,900 new plants and Yellow nutsedge: 1,900 new plants and

18,000 tubers in one year from one 18,000 tubers in one year from one plantplant

Get to know the enemy: weed identification

Weed identification goalsWeed identification goals

Impossible to learn the thousands of Impossible to learn the thousands of weeds found in Floridaweeds found in Florida

Learn the primary weedsLearn the primary weeds Keep field notesKeep field notes The goal is to learn how to identify a The goal is to learn how to identify a

weedweed Plant anatomyPlant anatomy Plant keysPlant keys

Weed classification: life Weed classification: life cyclescycles

Annuals- reproduce by seed onlyAnnuals- reproduce by seed only Biennial:Biennial:

Life cycle completed in two yearsLife cycle completed in two years Flowering and fruiting in second yearFlowering and fruiting in second year Examples: wild carrot, cudweedExamples: wild carrot, cudweed

Perrenials:Perrenials: Simple- reproduce by seed onlySimple- reproduce by seed only Creeping- reproduce by seed and Creeping- reproduce by seed and

vegetative propagulesvegetative propagules

Differences Differences between grasses between grasses and sedges:and sedges: Sedges have a solid, triangular in Sedges have a solid, triangular in

cross section, stem. Leaves are cross section, stem. Leaves are arranged in threes (extend in three arranged in threes (extend in three directions).directions).

Grass stems may be round or Grass stems may be round or flattened.flattened.

Purple vs Yellow NutsedgePurple vs Yellow Nutsedge

Purple vs Yellow NutsedgePurple vs Yellow Nutsedge

Common Common Sugarcane WeedsSugarcane Weeds

Fall panicumFall panicum ( (Panicum dichotomiflorumPanicum dichotomiflorum))

Most common grass in Most common grass in the areathe area Relatively easy to Relatively easy to

identifyidentify Stem can be hairy or Stem can be hairy or

smooth (hairy when smooth (hairy when young)young)

Ligule fringe of hairsLigule fringe of hairs Round stemRound stem Widely dispersed Widely dispersed

seedheadseedhead

Wild oats (Wild oats (Sorghum almumSorghum almum))

Not really an oatNot really an oat Closely related to Closely related to

johnsongrassjohnsongrass No rhizomesNo rhizomes Large, membranous Large, membranous

liguleligule Robust plantRobust plant

Can look like sugarcane Can look like sugarcane seedling when smallseedling when small

Broadleaf panicum Broadleaf panicum Panicum Panicum

adspersum adspersum ((Urochloa adspersaUrochloa adspersa)) Relatively prostrate Relatively prostrate

growthgrowth Wide leaves with Wide leaves with

wavy marginswavy margins Round stemsRound stems Usually dark green in Usually dark green in

colorcolor Very similar to Very similar to

alexandergrassalexandergrass

Alexandergrass Alexandergrass ((Brachiaria Brachiaria

plantagineaplantaginea)) Relatively prostrate Relatively prostrate

growthgrowth Somewhat wide leaves Somewhat wide leaves

with straight marginswith straight margins Round stemsRound stems Usually light green in colorUsually light green in color Very similar to broadleaf Very similar to broadleaf

panicumpanicum leaves narrower (usually)leaves narrower (usually) margins straight rather than margins straight rather than

wavy (usually)wavy (usually)

Alexandergrass vs Broadleaf Alexandergrass vs Broadleaf panicumpanicum

NapiergrassNapiergrass((Pennisetum pupureumPennisetum pupureum))

Very robust plantVery robust plant Forms dense clumps Forms dense clumps

in fieldsin fields Long, wide leaves Long, wide leaves

with finely toothed with finely toothed marginmargin

Up to 12 feet tallUp to 12 feet tall Seedhead has “bottle Seedhead has “bottle

brush” appearancebrush” appearance

Paragrass (Paragrass (Brachiaria Brachiaria muticamutica))

Prostrate growing, medium size grassProstrate growing, medium size grass Long stems covered with hairsLong stems covered with hairs

Short hairs on leaf surfaceShort hairs on leaf surface Swollen nodesSwollen nodes Grows in very wet areasGrows in very wet areas

Often moves out of ditchesOften moves out of ditches Pasture grass in AfricaPasture grass in Africa

Paragrass (Paragrass (Brachiaria Brachiaria muticamutica))

Goosegrass (Goosegrass (Elusine indicaElusine indica))

Found in many fieldsFound in many fields Low growingLow growing

Very white, flattened Very white, flattened stemsstems

Looks like it has been Looks like it has been stepped onstepped on

Probably not Probably not competitivecompetitive

CrabgrassCrabgrass((Digitaria spp.Digitaria spp.))

Very wide first leafVery wide first leaf Initial clumping growth Initial clumping growth

progressing to prostrate, progressing to prostrate, tilleringtillering

Visible membranous liguleVisible membranous ligule Can be very hairy, or Can be very hairy, or

hairless, depending on hairless, depending on speciesspecies

TorpedograssTorpedograss((Panicum repensPanicum repens L.) L.)

Perennial with Perennial with robust, creeping, robust, creeping, sharply pointed sharply pointed rhizomes.rhizomes.

Leaf blade stiff and Leaf blade stiff and erect.erect.

Hairs on upper and Hairs on upper and lower leaf surface.lower leaf surface.

Seedheads with Seedheads with stiff, ascending stiff, ascending branches.branches.

Occurs in wet areas.Occurs in wet areas.

Spiny pigweed Spiny pigweed ((Amaranthus spinosusAmaranthus spinosus))

Most common pigweed Most common pigweed speciesspecies StickerweedStickerweed

Large, upright growth Large, upright growth habit, entire leaveshabit, entire leaves

Very evident spines Very evident spines located at nodeslocated at nodes

AlligatorweedAlligatorweed ( (Alternanthera Alternanthera philoxeroidesphiloxeroides))

Common in many Common in many areas of the EAAareas of the EAA Prefers wet areasPrefers wet areas Often spread by Often spread by

cultivationcultivation Low growingLow growing

Hollow stems when Hollow stems when growing in wet spotsgrowing in wet spots

Opposite leavesOpposite leaves Small white bloomsSmall white blooms

Common lambsquarters Common lambsquarters (Chenopodium album)(Chenopodium album)

Common some yearsCommon some years Usually during the cooler Usually during the cooler

months (Dec, Jan)months (Dec, Jan) Can be difficult to controlCan be difficult to control

Waxy leaf surfaceWaxy leaf surface Small “dots” of wax are Small “dots” of wax are

useful for IDuseful for ID Gives leaves a white-gray Gives leaves a white-gray

colorcolor Alternate leavesAlternate leaves Medium size lobes on Medium size lobes on

leavesleaves

Common purslaneCommon purslane((Portulaca oleraceaPortulaca oleracea))

Very commonVery common Probably not competitiveProbably not competitive Prostrate growingProstrate growing SucculentSucculent Leaves small, smooth, opposite or Leaves small, smooth, opposite or

alternatealternate Small, yellow flowersSmall, yellow flowers Red stemsRed stems

Common ragweedCommon ragweed((Ambrosia artemisiifoliaAmbrosia artemisiifolia))

Often found on ditch Often found on ditch banks and field edgesbanks and field edges Deeply dissected leavesDeeply dissected leaves Many hairs on upper Many hairs on upper

and lower surfacesand lower surfaces Long seedhead at top of Long seedhead at top of

plantplant Yellow flowersYellow flowers

Similar in appearance Similar in appearance to ragweed partheniumto ragweed parthenium

Different flower typeDifferent flower type

Ragweed partheniumRagweed parthenium((Parthenium Parthenium

hysterophorushysterophorus)) Primarily ditchbanksPrimarily ditchbanks

Less common than Less common than common ragweedcommon ragweed

Leaves less deeply Leaves less deeply dissecteddissected

Divisions don’t go all the Divisions don’t go all the way to the stemway to the stem

White flowersWhite flowers Single, not multiplesSingle, not multiples

American black nightshadeAmerican black nightshade((Solanum americanumSolanum americanum))

Occasional weed in EAAOccasional weed in EAA Problematic in vegetables (tomato, Problematic in vegetables (tomato,

pepper)pepper) Same family (Solanaceae)Same family (Solanaceae) Resistant to paraquat in some areasResistant to paraquat in some areas

Alternate leavesAlternate leaves Usually entire to somewhat lobedUsually entire to somewhat lobed

Purple fruitPurple fruit Seems quite competitiveSeems quite competitive

American black nightshadeAmerican black nightshade((Solanum americanumSolanum americanum))

Sources of Weed ID Sources of Weed ID InformationInformation

Picture books:Picture books: Southern Weed Science Society ID Southern Weed Science Society ID

GuideGuide Excellent resourceExcellent resource

Very thorough (almost too many plants)Very thorough (almost too many plants)

Web Picture/Taxonomic SitesWeb Picture/Taxonomic Sites http://aquat1.ifas.ufl.edu/photos.htmlhttp://aquat1.ifas.ufl.edu/photos.html http://www.griffin.peachnet.edu/cssci/TURF/http://www.griffin.peachnet.edu/cssci/TURF/

turf.htmturf.htm

Weed management

strategies

Secrets to Successful Weed Secrets to Successful Weed ControlControl

1.1. PreventionPrevention

2.2. PreventionPrevention

3.3. PreventionPrevention

OnlyOnly you you can prevent weed can prevent weed invasion!invasion!

Be careful what you plant Be careful what you plant Consider all points of entryConsider all points of entry Keep an eye out for new invaders Keep an eye out for new invaders

elsewhereelsewhere Prevent reproduction of early Prevent reproduction of early

invadersinvaders

Ecological weed management Ecological weed management is based on how a plant is builtis based on how a plant is built

Annual vs. biennial vs. perennialAnnual vs. biennial vs. perennial Growth stage – perennials act like Growth stage – perennials act like

annuals for a short periodannuals for a short period Timing relative to the seasonsTiming relative to the seasons Control prior to seed productionControl prior to seed production

Management timing relative to Management timing relative to the seasonsthe seasons

Perennial weed growth schedule:Perennial weed growth schedule: Spring: export carbohydrates from roots Spring: export carbohydrates from roots

to new shootsto new shoots Summer: capture and assimilate new Summer: capture and assimilate new

energyenergy Fall: “pack it in” for winter – Fall: “pack it in” for winter –

carbohydrates transported to the rootscarbohydrates transported to the roots Winter: usually, minimal growth or Winter: usually, minimal growth or

activityactivity

Management timing relative to Management timing relative to the seasonsthe seasons

Perennial weed management – Perennial weed management – general terms:general terms: Spring: limit new growth – drain the Spring: limit new growth – drain the

rootsroots Summer: prevent energy captureSummer: prevent energy capture Fall: opportunity to attack the root Fall: opportunity to attack the root

storage systemstorage system Winter: eliminate new seedlingsWinter: eliminate new seedlings

Manual removalManual removalHoeing, Pulling, CultivationHoeing, Pulling, Cultivation

Success determined by population Success determined by population and distribution – is it feasible?and distribution – is it feasible?

Annual weeds easily removedAnnual weeds easily removed Perennial plants are often Perennial plants are often

“subdivided”“subdivided” Vegetative root pieces often produce Vegetative root pieces often produce

new plantsnew plants

Biological controlBiological control Biological control of weeds in cropping Biological control of weeds in cropping

systems is a difficult propositionsystems is a difficult proposition The control agent must be very host-The control agent must be very host-

specific and not injure non-target speciesspecific and not injure non-target species The life cycle of the control agent must The life cycle of the control agent must

match that of the target speciesmatch that of the target species Surrounding habitat should support control Surrounding habitat should support control

agent survival and reproductionagent survival and reproduction In the future, possibility of bioherbicidesIn the future, possibility of bioherbicides

HerbicidesHerbicides Several good Several good

options for most options for most crops grown in EAAcrops grown in EAA

Applications should Applications should be timed to be timed to minimize minimize competition with competition with cropcrop

Should be made Should be made prior to weed seed prior to weed seed head formationhead formation

Questions??Questions??