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Forestry Herbicide Forestry Herbicide Symptoms & Mode of Symptoms & Mode of ActionAction

John BoydUniversity of Arkansas

jboyd@uaex.edu501-671-2224

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What is mode of action?What is mode of action? How a herbicide disrupts or How a herbicide disrupts or

inhibits normal plant inhibits normal plant development.development.– Examples Examples

cell membrane destruction.cell membrane destruction. block protein synthesisblock protein synthesis interfere with photosynthesisinterfere with photosynthesis

33

Terms to rememberTerms to remember

photosynthesis (food)photosynthesis (food) respiration (energy)respiration (energy) amino acids (proteins/growth)amino acids (proteins/growth) lipids (cell membranes)lipids (cell membranes) pigments (energy/light capture)pigments (energy/light capture) mitosis (cell division)mitosis (cell division)

44

Phloem mobile herbicides move up and down in the plant

Xylem mobile herbicides move up in the plant

Contact herbicides do not move in the plant

Contact

55

Growth Regulator HerbicidesGrowth Regulator Herbicides

FamilyFamily Common NameCommon Name Trade NameTrade Name

PhenoxyPhenoxy 2,4-D2,4-D SeveralSeveral

benzoic acidbenzoic acid dicambadicamba VanquishVanquish

carboxylic acidcarboxylic acid piclorampicloram TordonTordon

carboxylic acidcarboxylic acid triclopyrtriclopyr GarlonGarlon

carboxylic acidcarboxylic acid clopyralidclopyralid TranslineTransline

Affect cell division, cell enlargement, protein Affect cell division, cell enlargement, protein synthesis and respiration. Act by upsetting hormone synthesis and respiration. Act by upsetting hormone balance.balance.

66

Growth Regulator HerbicidesGrowth Regulator Herbicides

Generally applied to leaves, but Generally applied to leaves, but have limited soil activityhave limited soil activity

Length of soil activity is herbicide-Length of soil activity is herbicide-dependentdependent

Highly systemic in susceptible Highly systemic in susceptible plants plants

Activity (pound for pound) varies Activity (pound for pound) varies among herbicidesamong herbicides

Primarily broadleaf activity but Primarily broadleaf activity but may affect grassesmay affect grasses

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Growth Regulator SymptomsGrowth Regulator Symptoms

Broadleaf plant stem twisting and curlingBroadleaf plant stem twisting and curling Leaves on broadleaf plants exhibit Leaves on broadleaf plants exhibit

cupping, crinkling, strapping, or cupping, crinkling, strapping, or drawstring affectdrawstring affect

Symptoms on grass plants include leaf Symptoms on grass plants include leaf rolling, crinkling, brace root fusion and rolling, crinkling, brace root fusion and malformation. malformation.

Also, flower sterility and missing grain in Also, flower sterility and missing grain in crops.crops.

88

Twisting of stems and leaf cupping are typical symptoms of the growth regulator herbicides.

99Leaf strapping is another typical symptom of these herbicides.

1010

Deformed pin oak leaf caused by 2,4-D. This is referred to as the drawstring effect.

1111Vanquish (dicamba)

untreated

1212

Upward cupping of leaves on azalea. Common symptom with dicamba exposure.

1313

Upward cupping of Upward cupping of leaves on lilac from 2,4-D leaves on lilac from 2,4-D exposure.exposure.

1414

Photosynthesis InhibitorsPhotosynthesis Inhibitors

FamilyFamily Common Common NameName

Trade NameTrade Name

triazinetriazine atrazineatrazine AAtrexAAtrex

triazinetriazine simazinesimazine PrincepPrincep

triazinonetriazinone hexazinonehexazinone VelparVelpar

uraciluracil bromacilbromacil HyvarHyvar

ureaurea diurondiuron KarmexKarmex

ureaurea tebuthiurontebuthiuron SpikeSpikeThese herbicides interrupt photosynthesis the process These herbicides interrupt photosynthesis the process by which green plants convert light energy into food. by which green plants convert light energy into food.

1515

PI’s are Xylem MobilePI’s are Xylem Mobile

Velpar, atrazine, simazine, Spike, Velpar, atrazine, simazine, Spike, HyvarHyvar– Taken up by primarily by roots.Taken up by primarily by roots.– Symptoms appear in older leaves Symptoms appear in older leaves

that are exporting sugarsthat are exporting sugars– Do not move downward when foliar Do not move downward when foliar

applied.applied.

1616

Photosynthesis InhibitorsPhotosynthesis Inhibitors

Most PI’s are soil applied.Most PI’s are soil applied. All PI’s have at least some All PI’s have at least some

postemergence activitypostemergence activity Soil-applied PI’s translocate Soil-applied PI’s translocate

through the xylem.through the xylem.

1717

Interveinal or veinal yellowing Interveinal or veinal yellowing followed by death of plant tissue followed by death of plant tissue from leaf margins inwardfrom leaf margins inward

Postemergence applications Postemergence applications cause rapid burning of plant cause rapid burning of plant tissuetissue

Photosynthesis InhibitorsPhotosynthesis Inhibitors

1818

Princep (simazine)Princep (simazine)

Symptoms often appear on the margins of the oldest leaves (pear).

1919

Karmex (diuron) on oak. Symptoms often appear on the margins of the oldest leaves.

2020

With photosynthesis inhibitors, symptoms start on the margins of the older leaves and move inward.

2121

With photosynthesis inhibitors, symptoms start on the margins of the older leaves and move inward.

2222

Pigment Inhibitor HerbicidesPigment Inhibitor Herbicides

FamilyFamily Common Common NameName

Trade NameTrade Name

isoxazolidinonisoxazolidinonee

clomazoneclomazone CommandCommand

pyridazinonepyridazinone norflurazonnorflurazon SolicamSolicam

not classifieldnot classifield fluridonefluridone SonarSonar

These herbicides cause the green pigments (chlorophyll) These herbicides cause the green pigments (chlorophyll) in plants to be destroyed. Without chlorophyll, plants in plants to be destroyed. Without chlorophyll, plants cannot photosynthesize and will die. cannot photosynthesize and will die.

2323

Pigment inhibitorsPigment inhibitors

Pigment inhibitors cause white leaves Pigment inhibitors cause white leaves in susceptible plantsin susceptible plants

New growth will not contain the green New growth will not contain the green pigments needed for photosynthesispigments needed for photosynthesis

Symptoms may be found on the Symptoms may be found on the cotyledon leaves and true leavescotyledon leaves and true leaves

White growth may be observed within White growth may be observed within veins (primarily with Zorial) and veins (primarily with Zorial) and between veins (primarily with between veins (primarily with Command)Command)

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Pigment Inhibitor HerbicidesPigment Inhibitor Herbicides

Zorial (norflurazon).Zorial (norflurazon). Inhibit carotenoid Inhibit carotenoid

formation followed by formation followed by loss of chlorophyll.loss of chlorophyll.

New growth is white, New growth is white, sometimes tinged with sometimes tinged with pink or purple.pink or purple.

Zorial usually follows Zorial usually follows the leaf veins.the leaf veins.

ZorialZorial

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Command (clomazone)Command (clomazone)

New growth is New growth is white, white, sometimes sometimes tinged with tinged with pink or pink or purple.purple.

Command: Command: white white between the between the veins.veins. Maple

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Root Growth InhibitorsRoot Growth Inhibitors

FamilyFamily Common Common NameName

Trade NameTrade Name

dinitroanilinedinitroaniliness

oryzalinoryzalin SurflanSurflan

dinitroanilinedinitroaniliness

pendimethalipendimethalinn

PendulumPendulum

dinitroanilinedinitroaniliness

prodiamineprodiamine BarricadeBarricadeThe root inhibitors interrupt cell division (mitosis) stopping root growth in seedling plants.

2727

Root Growth InhibitorsRoot Growth Inhibitors Plant death generally occurs before Plant death generally occurs before

emergenceemergence Root inhibitors translocate very littleRoot inhibitors translocate very little Generally stable in upper soil profile Generally stable in upper soil profile Persistence is herbicide-dependentPersistence is herbicide-dependent Most effective on small-seeded grass Most effective on small-seeded grass

and broadleaf weedsand broadleaf weeds

2828

Root Growth InhibitorsRoot Growth Inhibitors

Roots on susceptible plants will be stubby Roots on susceptible plants will be stubby and thick, especially lateral rootsand thick, especially lateral roots

Root limitation may cause stunting of plants Root limitation may cause stunting of plants and phosphorus deficiency symptomsand phosphorus deficiency symptoms

Broadleaf plants may have swollen Broadleaf plants may have swollen hypocotylshypocotyls

Concentration of herbicide at soil surface Concentration of herbicide at soil surface may cause callus tissue to form, leading to may cause callus tissue to form, leading to plant lodgingplant lodging

2929

Roots on susceptible plants will be stubby and thick, especially lateral roots

3030

Cell Membrane DisruptersCell Membrane Disrupters

FamilyFamily Common Common NameName

Trade NameTrade Name

bipyridiliumsbipyridiliums diquatdiquat RewardReward

bipyridiliumsbipyridiliums paraquatparaquat GramoxoneGramoxone

diphenylethediphenylethersrs

lactofenlactofen CobraCobra

Destroy cell membranes, causing cell contents to Destroy cell membranes, causing cell contents to leak out and result in desiccation of plant tissue. leak out and result in desiccation of plant tissue.

3131

Contact herbicidesContact herbicides Do not moveDo not move Herbicides: Paraquat, diquat, Herbicides: Paraquat, diquat,

Cobra (lactofen), MSMACobra (lactofen), MSMA– Rupture cell walls.Rupture cell walls.– Symptoms appear within hours. Symptoms appear within hours.

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Cell Membrane Disruptors & Cell Membrane Disruptors & ArsenicalsArsenicals

Rapid yellowing followed by Rapid yellowing followed by desiccation of affected plant tissuedesiccation of affected plant tissue

MSMA, DSMA symptoms generally MSMA, DSMA symptoms generally appear first on leaf tipsappear first on leaf tips

Drift may result in speckled leaf burnDrift may result in speckled leaf burn

3333

Paraquat drift on pecan causes speckling of the leaves.

3434

Organic ArsenicalsOrganic Arsenicals

FamilyFamily Common Common NameName

Trade NameTrade Name

organic organic arsenicalsarsenicals

MSMAMSMA SeveralSeveral

organic organic arsenicalsarsenicals

DSMADSMA SeveralSeveral

Fast acting herbicides that produce rapid leaf burn.

3535

Lipid Synthesis InhibitorsLipid Synthesis Inhibitors(Grass Specific Herbicides)(Grass Specific Herbicides)

FamilyFamily Common NameCommon Name Trade NameTrade Name

cyclohexanedionecyclohexanedione sethoxydimsethoxydim PoastPoast

cyclohexanedionecyclohexanedione clethodimclethodim EnvoyEnvoy

aryloxyphenoxy- aryloxyphenoxy- propionatepropionate

fluazifop-Pfluazifop-P FusiladeFusilade

aryloxyphenoxy- aryloxyphenoxy- propionatepropionate

fenoxaprop-Pfenoxaprop-P Acclaim ExtraAcclaim Extra

These herbicides act by disrupting lipid biosynthesis in These herbicides act by disrupting lipid biosynthesis in grass plants. Plant cells and cellular organelles all contain grass plants. Plant cells and cellular organelles all contain lipid membranes. Therefore, these herbicides affect cell lipid membranes. Therefore, these herbicides affect cell membrane integrity in the meristems.membrane integrity in the meristems.

3636Grass herbicides symptoms on johnsongrass

3737

Grass Specific HerbicidesGrass Specific Herbicides

Initial injury in the meristems occurs Initial injury in the meristems occurs where new leaves are developingwhere new leaves are developing

These regions will turn chlorotic, These regions will turn chlorotic, which is followed by necrosiswhich is followed by necrosis

The affected area will become rotten The affected area will become rotten and will easily separate from rest of and will easily separate from rest of plantplant

Injury will develop slowly (7 to 14 Injury will develop slowly (7 to 14 days)days)

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Grass Herbicide SymptomsGrass Herbicide Symptoms

Reddening of leaf tissue.Reddening of leaf tissue. Discoloration of tissue at and above the Discoloration of tissue at and above the

nodes.nodes. Tissue and leaves in the leaf whorl can Tissue and leaves in the leaf whorl can

easily be separated from the rest of the easily be separated from the rest of the plant.plant.

No broadleaf activity.No broadleaf activity.

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Amino Acid Synthesis Amino Acid Synthesis InhibitorsInhibitors(ALS inhibitors)(ALS inhibitors)

FamilyFamily Common Common NameName

Trade NamesTrade Names

imidazolinonesimidazolinones imazapyrimazapyr Arsenal, Arsenal, Chopper Chopper StalkerStalker

sulfonylureasulfonylurea metsulfuronmetsulfuron EscortEscort

sulfonylureasulfonylurea sulfometuronsulfometuron OustOustThese herbicides inhibit amino acid synthesis which is These herbicides inhibit amino acid synthesis which is necessary for the formation of plant proteins. necessary for the formation of plant proteins.

4040

ALS CharacteristicsALS Characteristics

Most of these herbicides have soil Most of these herbicides have soil and foliar activity except and foliar activity except glyphosate, and glufosinate glyphosate, and glufosinate

Systemically translocated in Systemically translocated in plantsplants

Soil activity herbicide-dependentSoil activity herbicide-dependent Generally, low use-rate herbicidesGenerally, low use-rate herbicides

4141

ALS SymptomsALS Symptoms

Grass symptoms include: stunting, Grass symptoms include: stunting, purple coloration, and inhibited root purple coloration, and inhibited root systems with bottle-brush appearancesystems with bottle-brush appearance

Broadleaf symptoms include: red or Broadleaf symptoms include: red or purple veins, yellowing of new leaves purple veins, yellowing of new leaves and blackened terminal growthand blackened terminal growth

Glyphosate injury includes initial Glyphosate injury includes initial yellowing followed by death of yellowing followed by death of affected tissueaffected tissue

4242

Amino Acid Synthesis Amino Acid Synthesis InhibitorsInhibitors Accord, Arsenal, Oust, Escort,Accord, Arsenal, Oust, Escort, Move to points of active growth or Move to points of active growth or

food storage.food storage. Affect shoot tips, young buds and Affect shoot tips, young buds and

leaves.leaves. Can cause contact burn and Can cause contact burn and

twisting.twisting.

4343

Arsenal (imazapyr)Arsenal (imazapyr)

Compact growth on azalea

Untreated

4444

Arsenal (imazapyr)Arsenal (imazapyr)

Bunched, compact growth on dogwood and sassafrass

4545

Arsenal symptoms on maple.

4646

Arsenal (imazpyr)Arsenal (imazpyr)

blackberry sweetgum

4747

Amino Acid Synthesis Amino Acid Synthesis InhibitorsInhibitors(Not ALS inhibitors)(Not ALS inhibitors)

FamilyFamily Common Common NameName

Trade NamesTrade Names

Not classifiedNot classified glyphosateglyphosate Accord, Accord, RoundupRoundup

Not classifiedNot classified sulfosatesulfosate TouchdownTouchdown

Not classifiedNot classified glufosinateglufosinate FinaleFinale

4848

Yellowing of new growth is common symptom of glyphosate exposure.

4949

Split bark on apple from Roundup exposure.

5050

Strapped leaves on maple due to Roundup.

5151Roundup drift from the previous fall may cause strapped Roundup drift from the previous fall may cause strapped leaves on peaches, apples and pears the next spring.leaves on peaches, apples and pears the next spring.

5252Stunted, compact growth due to

glyphosate.

5353Finale (glufosinate) on pine

5454Terminal damage from a tank mix of Accord + Arsenal