herbicide mode of action - agronomy...

Herbicide Mode of Herbicide Mode of ActionAction

Greg MacDonaldGreg MacDonaldUniversity of FloridaUniversity of Florida

Chemical Chemical -- HerbicidesHerbicides•• over 150 active ingredients registeredover 150 active ingredients registered•• over 4000 trade namesover 4000 trade names•• herbicides account for 55% of herbicides account for 55% of

pesticide usepesticide use

Names on the LabelNames on the Label

•• Trade nameTrade name -- marketing; lives with marketing; lives with the life of the productthe life of the product

•• Common nameCommon name -- active ingredient(s)active ingredient(s)•• Chemical nameChemical name –– IUPAC approved IUPAC approved

name, internationally recognizedname, internationally recognized

Herbicide HistoryHerbicide History•• Carthage Carthage -- 100 B.C. (salted the ground)100 B.C. (salted the ground)•• Copper SOCopper SO44, sulfuric acid, salts , sulfuric acid, salts -- late late

1800s1800s•• petroleum oils, Stoddardpetroleum oils, Stoddard’’s Solvents Solvent-- 19001900’’ss•• 2,4,62,4,6--dinitrophenol dinitrophenol -- 19321932•• 2,42,4--D D --19441944

HerbicidesHerbicides•• Herbicide is a chemical compound, Herbicide is a chemical compound,

generally organic, that is used to control generally organic, that is used to control plants. plants.

•• Chemistry of the herbicide dictatesChemistry of the herbicide dictates --–– how it works in the planthow it works in the plant–– how it behaves in the environmenthow it behaves in the environment–– how it can be stored, mixed and appliedhow it can be stored, mixed and applied

Application MethodsApplication Methods

•• prepre--plant, preplant, pre--plant incorporated, plant incorporated, preemergencepreemergence

•• atat--cracking, early postemergencecracking, early postemergence•• midmid--post, late post, post, late post, laybylayby, , salvagesalvage•• postpost--directed, shielded sprays, directed, shielded sprays, ropewickropewick

Application MethodsApplication Methods•• Apply to the soil or water Apply to the soil or water -- taken by plant taken by plant

roots or seedlingsroots or seedlings•• Apply to the leaves, bark, stemApply to the leaves, bark, stem•• contact herbicides contact herbicides -- only what they hitonly what they hit•• systemic herbicides systemic herbicides -- throughout plantthroughout plant•• placement selectivity can be achieved at placement selectivity can be achieved at

either level but either level but ……………………………………... ... need to need to know the herbicideknow the herbicide

FormulationsFormulations•• water soluble, oil soluble, salts, esterswater soluble, oil soluble, salts, esters•• clay suspension, pellets, granules, clay suspension, pellets, granules,

wettablewettable powders, powders, emusifiableemusifiableconcentratesconcentrates

•• the goal of the formulation is tothe goal of the formulation is to: store, : store, mix/spray in water, get it in the plant, and mix/spray in water, get it in the plant, and minimize offminimize off--target damagetarget damage

Persistence/Environmental FatePersistence/Environmental Fate

•• Factors affecting herbicide persistence in Factors affecting herbicide persistence in the environment:the environment:–– physical processesphysical processes–– chemical processeschemical processes–– biological processesbiological processes


•• Physical Processes Physical Processes -- VOLATILTYVOLATILTY–– temperature, soil moisture & composition temperature, soil moisture & composition –– as temperature increases, volatilization as temperature increases, volatilization

increases increases –– generally less volatilization in moist soil, but generally less volatilization in moist soil, but

can have volatilization in wet, heavy soilscan have volatilization in wet, heavy soils–– less volatilization in heavier soils w/ high OMless volatilization in heavier soils w/ high OM


•• Physical Processes Physical Processes -- LEACHINGLEACHING–– most movement is downward, but can be most movement is downward, but can be

upward (capillary flow)upward (capillary flow)–– affected byaffected by: soil texture, colloidal adsorption, : soil texture, colloidal adsorption,

water solubility of herbicide, chemical chargewater solubility of herbicide, chemical charge–– more leaching in sandy soils with low OMmore leaching in sandy soils with low OM

•• Physical Processes Physical Processes -- EROSIONEROSION–– runoff where the herbicide moves with the soilrunoff where the herbicide moves with the soil


•• physical processes physical processes --–– volatility volatility -- hot and windy hot and windy ↑↑–– leaching leaching -- sandy soils, high rain sandy soils, high rain ↑↑–– erosion erosion -- high rain in short time high rain in short time ↑↑


•• Chemical Processes Chemical Processes -- ADSORPTIONADSORPTION–– herbicides poorly adsorbed to sand, siltherbicides poorly adsorbed to sand, silt–– highly adsorbed to clays and organic matterhighly adsorbed to clays and organic matter–– reduces the amount herbicide available to reduces the amount herbicide available to

plants, slows leaching, retards breakdownplants, slows leaching, retards breakdown–– greatly influenced by soil pH (greatly influenced by soil pH (pKapKa’’ss, charges), charges)


•• Chemical Processes Chemical Processes --PhotodecompositionPhotodecomposition–– degradation by sunlight (generally UV light)degradation by sunlight (generally UV light)

•• Chemical Processes Chemical Processes -- HYDROLYSISHYDROLYSIS–– molecules in the soil or water chemically react molecules in the soil or water chemically react

with the herbicide, breaking the herbicide with the herbicide, breaking the herbicide downdown


•• chemical processes chemical processes ––adsorption adsorption -- sandy soils, variable pH sandy soils, variable pH ↓↓––photodecomposition photodecomposition -- high light high light ↑↑––hydrolysishydrolysis


•• Biological Processes Biological Processes -- MICROBIALMICROBIAL–– microbes use the herbicide as a food sourcemicrobes use the herbicide as a food source–– generally a favorable process, but can be generally a favorable process, but can be

detrimental (breakdown too quickly detrimental (breakdown too quickly -- lose lose weed control)weed control)

–– soil temperature, aeration, pH, moisture affect soil temperature, aeration, pH, moisture affect microbial activity and herbicide breakdownmicrobial activity and herbicide breakdown

•• Biological Processes Biological Processes -- DETOXIFICATIONDETOXIFICATION


•• biological processesbiological processes––microbial microbial -- high temp., humidity high temp., humidity ↑↑––detoxificationdetoxification

Herbicides Herbicides -- BackgroundBackground•• grouped according to chemical family grouped according to chemical family

(structure) (structure) -- generally relates to activity, generally relates to activity, but not alwaysbut not always………………somewhat confusingsomewhat confusing

•• can also be grouped by how they work to can also be grouped by how they work to control plants control plants (mode of action) (mode of action) –– this is this is how herbicides will be classified and how herbicides will be classified and explained in this classexplained in this class

How herbicides workHow herbicides work•• Controlled/selective plant poisoningControlled/selective plant poisoning

–– applied to soil (root uptake) and/or applied to soil (root uptake) and/or leavesleaves

–– contact or systemiccontact or systemic–– selective vs. nonselective vs. non--selectiveselective

•• each herbicide has unique properties, each herbicide has unique properties, some more environmentally friendly some more environmentally friendly

Mode vs. MechanismMode vs. Mechanism•• modemode--ofof--actionaction ---- symptoms that occur symptoms that occur

after herbicide application leading to plant after herbicide application leading to plant deathdeath

•• mechanismmechanism--ofof--actionaction ---- actual actual biochemical site of herbicide activitybiochemical site of herbicide activity–– generally enzyme or cogenerally enzyme or co--factorfactor–– in some cases actual in some cases actual ‘‘sitesite’’ is unknownis unknown

More Detailed More Detailed SymptomologySymptomology

•• contact vs. systemic herbicidescontact vs. systemic herbicides–– contact herbicides only affect what they hitcontact herbicides only affect what they hit–– systemic herbicides move throughout the systemic herbicides move throughout the

plantplant•• some systemic herbicides only move up some systemic herbicides only move up

from the roots to the leaves in the water from the roots to the leaves in the water streamstream

•• other systemic herbicides move both up other systemic herbicides move both up and down, track to areas of growthand down, track to areas of growth

Herbicide/Plant InteractionsHerbicide/Plant Interactions•• Selectivity Selectivity –– differences in the response differing differences in the response differing

plant species to a herbicideplant species to a herbicide–– Placement Placement –– crop does not take up the herbicide while crop does not take up the herbicide while

the weeds do.the weeds do.•• Time Time –– before the crop emergesbefore the crop emerges•• Spatial Spatial –– located away from crop (hooded sprayer)located away from crop (hooded sprayer)

–– Differential uptake Differential uptake –– crop takes up less herbicidecrop takes up less herbicide–– Metabolism Metabolism –– plant breaks down herbicide via oxidation, plant breaks down herbicide via oxidation,

dehydroxylationdehydroxylation, reduction, reduction•• Glutathione or amino acid conjugationGlutathione or amino acid conjugation•• Sequestration in vacuoleSequestration in vacuole

–– Differential binding at the enzyme level Differential binding at the enzyme level –– the herbicide the herbicide binds to the weed enzyme but not the crop enzymebinds to the weed enzyme but not the crop enzyme

Herbicide SelectivityHerbicide Selectivity•• placement placement -- keep it away from keep it away from

desirable plantdesirable plant•• uptake uptake -- apply so it doesnapply so it doesn’’t get in and t get in and

movemove•• metabolism metabolism -- some plants breakdown some plants breakdown

herbicides butherbicides but……. . ……•• target site is differenttarget site is different

Sequestered in vacuoleSequestered in vacuoleX does not X does not binds to binds to enzyme Yenzyme Y

Herbicide X Herbicide X not absorbednot absorbed

XX

X metabolized to ZX metabolized to Z

Y1Y1

Mechanisms of ToleranceMechanisms of Tolerance

W.H. Freeman and Sinauer Associates

Plant ProcessesPlant Processes1.1. photosynthesisphotosynthesis2.2. amino acids and proteins amino acids and proteins 3.3. fatty acid synthesisfatty acid synthesis4.4. growth inhibitiongrowth inhibition5.5. cell membranescell membranes6.6. pigment synthesispigment synthesis7.7. growth regulationgrowth regulation

1. Photosynthesis1. Photosynthesis•• process where the plant uses light energy process where the plant uses light energy

to convert COto convert CO22 and Hand H22O to sugars, release O to sugars, release OO22

•• Light reactionsLight reactions–– chlorophyll absorbs lightchlorophyll absorbs light–– passes energy down a biochemical chainpasses energy down a biochemical chain–– form intermediates to drive sugar formationform intermediates to drive sugar formation

Herbicides Herbicides -- PhotosynthesisPhotosynthesis•• block the flow of energy from chlorophyll to block the flow of energy from chlorophyll to

the intermediatesthe intermediates–– plant cannot make sugars plant cannot make sugars -- starvesstarves–– chlorophyll continues to absorb light and this chlorophyll continues to absorb light and this

‘‘excessexcess’’ energy forms toxic intermediates energy forms toxic intermediates •• generally soil active, root uptake and generally soil active, root uptake and

movement through water stream to leavesmovement through water stream to leaves

Substituted Substituted UreasUreas•• DiuronDiuron ((KarmexKarmex), ), tebuthiurontebuthiuron (Spike)(Spike)•• used in a variety of cropping systems for used in a variety of cropping systems for

broadleaf and some grass controlbroadleaf and some grass control•• mostly soil applied, but some foliar activitymostly soil applied, but some foliar activity•• root uptake, translocation via water root uptake, translocation via water

stream, little movement from foliar stream, little movement from foliar applicationsapplications

•• potent inhibitors of photosynthesispotent inhibitors of photosynthesis

TriazinesTriazines•• atrazineatrazine, , prometonprometon ((PramitolPramitol))•• wide variety of crops wide variety of crops -- corn, fruits, corn, fruits,

beansbeans……and and noncroplandnoncropland areas.areas.•• mostly soil applied, but some foliar activitymostly soil applied, but some foliar activity•• root uptake, translocation via water root uptake, translocation via water



UracilsUracils•• bromacilbromacil and and terbacilterbacil ((SinbarSinbar))•• noncroplandnoncropland, fruit and nuts, some forage, fruit and nuts, some forage•• mostly soil applied, but some foliar activitymostly soil applied, but some foliar activity•• root uptake, translocation via water root uptake, translocation via water



BenzonitrilesBenzonitriles•• bromoxynilbromoxynil -- POST in corn, BXN cottonPOST in corn, BXN cotton•• primarily broadleaf control, contact activityprimarily broadleaf control, contact activity•• inhibits photosynthesisinhibits photosynthesis•• dichlobenildichlobenil -- PRE in ornamentals, fruit, PRE in ornamentals, fruit,

aquatics (grass, sedge, some BL activity)aquatics (grass, sedge, some BL activity)•• causes severe stunting, blocks cell plate causes severe stunting, blocks cell plate

formation in dividing cellsformation in dividing cells

CarbamatesCarbamates•• desmediphamdesmedipham & & phenmediphamphenmedipham --

POST POST •• BL weed control in sugar beets and BL weed control in sugar beets and

veggiesveggies•• inhibit photosynthesisinhibit photosynthesis•• asulamasulam -- POST BL and grass weed POST BL and grass weed

control in certain turf, sugarcane, alfalfa control in certain turf, sugarcane, alfalfa and flaxand flax

•• mitotic inhibitor, prevents cell divisionmitotic inhibitor, prevents cell division

BentazonBentazon•• used postemergence in corn, soybeans, used postemergence in corn, soybeans,

rice, and several veggies for BL weeds rice, and several veggies for BL weeds and yellow and yellow nutsedgenutsedge controlcontrol

•• little movement within the plant, contact little movement within the plant, contact activityactivity

•• inhibits photosynthesisinhibits photosynthesis

Photosynthesis Photosynthesis –– SymptomsSymptoms

2. Amino acids and Proteins2. Amino acids and Proteins•• essential building blocks for plant growth essential building blocks for plant growth

and functionand function•• unlike animals, plants make their ownunlike animals, plants make their own•• amino acids are the primary components amino acids are the primary components

of proteins and nucleic acidsof proteins and nucleic acids•• proteins are generally storage proteins or proteins are generally storage proteins or

enzymesenzymes

Herbicides Herbicides -- Amino AcidsAmino Acids

•• generally target a specific enzyme generally target a specific enzyme –– blocks a vital step in the formation of amino blocks a vital step in the formation of amino

acidsacids---- proteins, enzymesproteins, enzymes……–– aromatic amino acidsaromatic amino acids–– branched chain amino acidsbranched chain amino acids

•• dependent on plant growth for activitydependent on plant growth for activity–– better growth better growth -- better control, slow deathbetter control, slow death

•• systemic herbicides, some have soil systemic herbicides, some have soil activityactivity

ImidazolinonesImidazolinones•• Imazapyr (Arsenal, Habitat), Imazapyr (Arsenal, Habitat), imazapicimazapic

(Plateau) -- crops & vegetation crops & vegetation managementmanagement

•• foliar & soil activity, used PPI, PRE or foliar & soil activity, used PPI, PRE or POST (soil activity can cause persistence)POST (soil activity can cause persistence)

•• grasses, BLgrasses, BL’’s and good s and good nutsedgenutsedge activityactivity•• accumulates in accumulates in meristematicmeristematic regionsregions•• inhibit the synthesis of the amino acids inhibit the synthesis of the amino acids

valinevaline, , leucineleucine, and , and isoleucineisoleucine

SulfonylureasSulfonylureas•• several herbicidesseveral herbicides-- low use rates, low use rates,

selectivity selectivity (Oust, Escort)(Oust, Escort)•• wide variety of crops & nonwide variety of crops & non--crop situationscrop situations•• PRE or POST PRE or POST -- broadleaf, grass and broadleaf, grass and

sedgessedges•• rapidly absorbed by roots, foliage rapidly absorbed by roots, foliage --

translocated throughout the plant and translocated throughout the plant and accumulates in accumulates in meristematicmeristematic regionsregions

•• inhibit the synthesis of the amino acids inhibit the synthesis of the amino acids valinevaline, , leucineleucine, and , and isoleucineisoleucine

SulfonanilidesSulfonanilides•• chloransulamchloransulam, , flumetsulamflumetsulam, , diclosulamdiclosulam•• PRE broadleaf weed control in corn, PRE broadleaf weed control in corn,

soybeans, peanuts, some POST activitysoybeans, peanuts, some POST activity•• rapidly absorbed by roots, foliage rapidly absorbed by roots, foliage --



PyrithiobacPyrithiobac•• labeled for PRE and POST use in cottonlabeled for PRE and POST use in cotton•• broadleaf weed control broadleaf weed control -- pigweeds, pigweeds, MGMG’’ss•• rapidly absorbed by roots, foliage rapidly absorbed by roots, foliage --



GlufosinateGlufosinate -- FinaleFinale•• postemergence postemergence broadspectrumbroadspectrum materialmaterial•• labeled for nolabeled for no--till, till, noncropnoncrop, and certain fruit , and certain fruit

and nut cropsand nut crops•• foliar uptake with limited translocationfoliar uptake with limited translocation•• blocks the incorporation of nitrogen in blocks the incorporation of nitrogen in

amino acids amino acids -- causes the buildup of toxic causes the buildup of toxic levels of ammoniumlevels of ammonium

glufosinateglufosinate

EntireleafEntireleaf morningglorymorningglory

CornCorn

glufosinateglufosinate

TomatoTomato

SoybeanSoybean

Glyphosate Glyphosate -- RoundupRoundup……etc.etc.•• broadspectrumbroadspectrum postemergence weed postemergence weed

controlcontrol•• glyphosate labeled in multitude of areasglyphosate labeled in multitude of areas•• For use in RoundupFor use in Roundup--Ready cropsReady crops•• extensively translocated throughout the extensively translocated throughout the

plant, extremely stable in plantplant, extremely stable in plant•• blocks synthesis of aromatic amino acidsblocks synthesis of aromatic amino acids

glyphosateglyphosate

glyphosateglyphosate

EntireleafEntireleaf morningglorymorningglory

Glyphosate injuryGlyphosate injuryon pecanson pecans

3. Fatty Acid Synthesis3. Fatty Acid Synthesis

•• Fatty acids are the primary building Fatty acids are the primary building components of cell membranes and many components of cell membranes and many intercellular membranes intercellular membranes

•• Inhibition of fatty acids results in stunted Inhibition of fatty acids results in stunted growth and eventually death due to lack of growth and eventually death due to lack of membranes for cellular integritymembranes for cellular integrity

ArylAryl--oxyoxy--PhenoxysPhenoxys &&CyclohexadionesCyclohexadiones

•• FusiladeFusilade, Select, Assure II, , Select, Assure II, PoastPoast•• registered in several crops, registered in several crops, noncroplandnoncropland•• grass activity only, postemergence grass activity only, postemergence •• translocated to growing portionstranslocated to growing portions•• inhibits fatty acid synthesis, slow deathinhibits fatty acid synthesis, slow death

Select/Select/FusiladeFusilade

johnsongrassjohnsongrass

CornCorn

Amides/Amides/ChloroacetamidesChloroacetamides•• MetolachlorMetolachlor (Dual), (Dual), pronamidepronamide ((DevrinolDevrinol))•• used PPI or PRE in several crops, control used PPI or PRE in several crops, control

grasses & certain broadleavesgrasses & certain broadleaves•• inhibit root and shoot growth through the inhibit root and shoot growth through the

inhibition of long chain fatty acid synthesisinhibition of long chain fatty acid synthesis

ThiocarbamatesThiocarbamates•• EPTC, EPTC, metammetam, etc., etc.•• nearly exclusively PPI due to volatilitynearly exclusively PPI due to volatility•• several crops several crops -- corn, rice, beans, noncorn, rice, beans, non--cropcrop•• mainly grasses, but some sedge and BLmainly grasses, but some sedge and BL’’ss•• root and shoot absorbed root and shoot absorbed -- germinating germinating

seedsseeds•• inhibition of inhibition of gibberellingibberellin plant hormone and plant hormone and

fatty acid synthesis fatty acid synthesis

4. Growth Inhibition4. Growth Inhibition

•• plants grow by making new cells plants grow by making new cells –– process of cell division, mitosisprocess of cell division, mitosis

•• plants are particularly susceptible as plants are particularly susceptible as emerging seedlingsemerging seedlings–– both shoot and rootsboth shoot and roots

•• newly forming roots can be susceptible at newly forming roots can be susceptible at most stages of plant growthmost stages of plant growth

Herbicides Herbicides -- Growth InhibitionGrowth Inhibition

•• most growth inhibition herbicides are soil most growth inhibition herbicides are soil applied and generally affect seedling applied and generally affect seedling weedsweeds

•• most interfere w/ mitosis (mitotic poisons)most interfere w/ mitosis (mitotic poisons)•• soil active, little movement once absorbedsoil active, little movement once absorbed

DinitroanalinesDinitroanalines•• ethalfluralinethalfluralin, , trifluralintrifluralin ((TreflanTreflan) ) •• Pendimethalin (Prowl), Pendimethalin (Prowl), oryzalinoryzalin ((SurflanSurflan))•• soil applied, PPI or PRE soil applied, PPI or PRE -- annual grasses annual grasses

and certain broadleaf weedsand certain broadleaf weeds•• vary in volatility and photodegradation vary in volatility and photodegradation •• prevent both root and shoot growth, inhibit prevent both root and shoot growth, inhibit

cell division (mitosis)cell division (mitosis)

DichlobenilDichlobenil and and IsoxabenIsoxaben•• dichlobenildichlobenil -- PRE in ornamentals, fruit PRE in ornamentals, fruit

(grass, sedge, some BL activity)(grass, sedge, some BL activity)•• causes severe stunting, blocks cell plate causes severe stunting, blocks cell plate

formation in dividing cellsformation in dividing cells•• isoxabenisoxaben –– PRE in ornamentals, fruit, PRE in ornamentals, fruit,

others (grass, some BL activity)others (grass, some BL activity)•• causes severe stunting, blocks cell wall causes severe stunting, blocks cell wall

formation in dividing cellsformation in dividing cells

5. Cell Membranes5. Cell Membranes•• maintain cell integritymaintain cell integrity

–– keep things in & outkeep things in & out•• generate electrochemical gradientsgenerate electrochemical gradients

–– allows for energy productionallows for energy production•• maintain cell structuremaintain cell structure

–– turgorturgor pressure maintains plant structure and pressure maintains plant structure and helps the plant growhelps the plant grow

Herbicides Herbicides -- Cell MembranesCell Membranes

•• divert normal energy flow to form toxic divert normal energy flow to form toxic intermediatesintermediates–– interact w/ membrane and cause disruptioninteract w/ membrane and cause disruption

•• cause the membrane to become cause the membrane to become ““leakyleaky””–– gradients cannot be formed, no energy for gradients cannot be formed, no energy for

cellular functions cellular functions -- endothallendothall•• generally contact, little movement in plantgenerally contact, little movement in plant

Organic ArsenicalsOrganic Arsenicals•• MSMA, DSMA, MSMA, DSMA, cacodyliccacodylic acid, CMAacid, CMA•• used postemergence in cotton, turfused postemergence in cotton, turf•• no soil activityno soil activity•• readily absorbed by leaves, translocated readily absorbed by leaves, translocated

to growing tipsto growing tips•• chlorosischlorosis, stunting, , stunting, dessicationdessication•• interferes with energy transfer, enzymesinterferes with energy transfer, enzymes

MSMAMSMA

johnsongrassjohnsongrass

CornCorn

BipyridylliumsBipyridylliums•• paraquat (paraquat (GramoxoneGramoxone) and ) and diquatdiquat

(Reward) -- several registrationsseveral registrations•• nonnon--selective postemergence activityselective postemergence activity•• little translocation, contactlittle translocation, contact•• diverts normal electron flow, causes diverts normal electron flow, causes

formation of radical oxygen and cell formation of radical oxygen and cell membrane disruptionmembrane disruption

•• no soil activityno soil activity

DQ DQH2

O2-

GramoxoneGramoxone

PPO inhibitorsPPO inhibitors•• FlumioxazinFlumioxazin (Valor), (Valor), SulfentrazoneSulfentrazone

(Spartan)& (Spartan)& CarfentrazoneCarfentrazone (Stingray) (Stingray) •• applied POST for BL weed controlapplied POST for BL weed control•• contact, no translocation in foliar contact, no translocation in foliar

treatments treatments •• xylem movement from soil activexylem movement from soil active•• increase of light absorbing intermediatesincrease of light absorbing intermediates•• formation of highly toxic free radicalsformation of highly toxic free radicals

Copper (Copper (ChelatesChelates, CuSO4), CuSO4)

•• Used for algae and submersed plant Used for algae and submersed plant control in aquatic situationscontrol in aquatic situations

•• CuSO4 more active, limited uses due to CuSO4 more active, limited uses due to fish problemsfish problems

•• Appears to disrupt cell membranes, but Appears to disrupt cell membranes, but exact mechanism is unknownexact mechanism is unknown

fomesafenfomesafen

TomatoTomato

IvyleafIvyleaf morningglorymorningglory

6. Pigment Synthesis6. Pigment Synthesis•• absorb light energy for photosynthesisabsorb light energy for photosynthesis•• also protect plant from excess lightalso protect plant from excess light•• types of pigmentstypes of pigments

–– chlorophyllchlorophyll–– carotenoidscarotenoids–– flavenoidsflavenoids–– anthocyaninsanthocyanins

HerbicidesHerbicides-- Pigment Pigment SynthesisSynthesis

•• block the formation of chlorophyllblock the formation of chlorophyll•• block the formation of block the formation of carotenoidscarotenoids

–– carotenoidscarotenoids accept excess energyaccept excess energy–– when absent, chlorophyll when absent, chlorophyll dissinegratesdissinegrates

•• generally slow death, plant starvesgenerally slow death, plant starves•• soil active, movement through water soil active, movement through water

streamstream

ClomazoneClomazone•• clomazoneclomazone labeled for use PPI (volatile) in labeled for use PPI (volatile) in

soybeans, tobacco, cotton certain veggies soybeans, tobacco, cotton certain veggies •• effective on grasses and certain BLeffective on grasses and certain BL’’ss•• root absorbed, bleaching of leaf tissueroot absorbed, bleaching of leaf tissue•• inhibits chlorophyll synthesisinhibits chlorophyll synthesis

PyridazinonesPyridazinones•• fluridonefluridone (Sonar)(Sonar) labeled for aquatic weed labeled for aquatic weed

controlcontrol•• norflurazonnorflurazon ((SolicamSolicam)) labeled PRE in cotton, labeled PRE in cotton,

beans, peanuts, fruit/nut crops beans, peanuts, fruit/nut crops -- BLBL’’s and s and grassesgrasses

•• root absorbed, translocated in water stream to root absorbed, translocated in water stream to growing points growing points -- bleaching of leaf tissuebleaching of leaf tissue

•• inhibit the synthesis of inhibit the synthesis of carotenoidscarotenoids (protective (protective plant pigments)plant pigments)

Other Pigment InhibitorsOther Pigment Inhibitors

•• MesotrioneMesotrione and and isoxaflutoleisoxaflutole•• Used preUsed pre--emergence and postemergence and post--emergence emergence

in corn for grass and broadleaf controlin corn for grass and broadleaf control•• Blocks the formation of a precursor Blocks the formation of a precursor

needed for needed for carotenoidcarotenoid synthesissynthesis•• Similar mode of action to the Similar mode of action to the

pyridazinonespyridazinones, but different mechanism, but different mechanism

Pigment Injury SymptomsPigment Injury Symptoms

Growth RegulationGrowth Regulation•• hormones control plant growth and hormones control plant growth and

developmental changes, always presentdevelopmental changes, always present•• grouped into 5 types grouped into 5 types -- but highly but highly

interactive interactive –– auxinsauxins (light responses, apical dominance)(light responses, apical dominance)–– giberrelinsgiberrelins (elongation, flowering)(elongation, flowering)–– cytokininscytokinins (growth, development)(growth, development)–– abscisicabscisic acid (leaf senescence, acid (leaf senescence, propagulepropagule

form.)form.)–– ethylene (leaf senescence, counteract auxin)ethylene (leaf senescence, counteract auxin)

Herbicides Herbicides -- Growth Growth RegulationRegulation

•• auxin mimics auxin mimics -- cause uncontrolled growthcause uncontrolled growth–– auxin transport inhibitorsauxin transport inhibitors–– prevent the normal distribution of auxinprevent the normal distribution of auxin

•• indirectly, all herbicides can be regulatorsindirectly, all herbicides can be regulators–– SonarSonar (fluridone) blocks (fluridone) blocks abscisicabscisic acidacid–– glyphosateglyphosate inhibits auxin regulationinhibits auxin regulation

•• soil and foliar applied, systemic throughoutsoil and foliar applied, systemic throughout

Benzoic AcidsBenzoic Acids•• dicamba (dicamba (BanvelBanvel, Clarity), Clarity)-- registered for registered for

use in corn, turf, pastures (broadleaf weed use in corn, turf, pastures (broadleaf weed control)control)

•• postemergence but possesses some soil postemergence but possesses some soil activity (can be used activity (can be used preemergencepreemergence in in corn)corn)

•• readily translocated to growing tipsreadily translocated to growing tips•• interferes with RNA, DNA and protein interferes with RNA, DNA and protein

synthesis synthesis -- leading to rapid, uncontrolled leading to rapid, uncontrolled growth (similar to growth (similar to phenoxysphenoxys))

dicambadicamba

Hemp Hemp SesbaniaSesbania

CucumberCucumber

dicambadicamba

CottonCotton

TomatoTomato

PhenoxysPhenoxys•• 2,42,4--D, 2,4D, 2,4--DB, 2,4DB, 2,4--DP, MCPADP, MCPA•• BL weed control for a variety of crops BL weed control for a variety of crops

(corn, pastures, legumes) and (corn, pastures, legumes) and noncroplandnoncropland

•• salt, ester and oil formulations salt, ester and oil formulations •• foliar & root uptakefoliar & root uptake-- extensive extensive

translocationtranslocation•• cells undergo rapid uncontrolled division cells undergo rapid uncontrolled division

and elongationand elongation

PicolinicPicolinic acidsacids•• Triclopyr (Triclopyr (GarlonGarlon), ), chlorpyralidchlorpyralid

((TranslineTransline), ), aminopyralidaminopyralid (Milestone)(Milestone)•• used POST for BL weed control, brush & used POST for BL weed control, brush &

woodywoody•• similar to similar to phenoxysphenoxys, primarily foliar applied , primarily foliar applied

but but piclorampicloram has tremendous soil activityhas tremendous soil activity•• foliar & root uptakefoliar & root uptake-- extensive extensive

translocationtranslocation•• cells undergo rapid uncontrolled division cells undergo rapid uncontrolled division

and elongationand elongation

triclopyrtriclopyr

CucumberCucumber

Redroot pigweedRedroot pigweed

DiflufenzopyrDiflufenzopyr•• labeled for POST use in corn, labeled for POST use in corn,

pasture/pasture/noncroplandnoncropland•• activity on broadleaves and grassesactivity on broadleaves and grasses•• foliar and root absorbed, translocated to foliar and root absorbed, translocated to

growing regionsgrowing regions•• mode of action not fully understood mode of action not fully understood --

appears to interfere with hormonal balanceappears to interfere with hormonal balance

herbicide mode of action - agronomy...

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