Dr. Michael Pfeiffer

Herbicide Mode of Action

Below are listed herbicides based on their modes of action on plants used in non-Ag situations. Injury symptoms on plantsis also provided. While every attempt has been made to be as precise as possible in describing injury symptoms on plants,it is impossible to describe every combination of plant/herbicide injury symptom. Due to space limitations, not all herbicidescould be included in this publication. The group of herbicides commonly known as pigment inhibitors has been left out.Apologies are extended to companies whose products are not mentioned.

' I. Amino Acid Synthesis InhibitorsSulfonylureas (Inhibit production of acetolactase synthase (ALS))Trade Name Common Name Trade Name Common Name Trade Name Common NameOutriderManorTransXit

sulfosulfuronmetsulfuronrimsulfuron

CorsairMonumentOust

chlorsulfurontrifloxysulfuronsulfometuron

KatanaRevolverSedgehammer

flazasulfuronforamsulfuronhalosulfuron

Imidazolinones (Inhibit production of acetolactase synthase (ALS))Trade Name Common Name Trade Name Common Name Trade Name Common NameArsenalChopper

imazapyrimazapyr

HabitatStalker

imazapyrimazapyr

PlateauImage

imazapicimazaquin

Glyphosate (Inhibits production of 5-enolpyruvyl-shikimate-3-phosphate synthase( EPSPS)Trade Name Common Name Trade Name Common Name Trade Name Common NameRoundupRattler

glyphosateglyphosate

GlyphomaxTouchdown

glyphosateglyphosate

Rodeo glyphosate

' II. GROWTH REGULATORS (Mimic natural growth regulatory compounds in plants:Numerous effects on plants)Phenoxy acidsTrade Name Common Name Trade Name Common Name Trade Name Common NameRhonoxRhomene

MCPAMCPA

MCPPvarious

mecoprop2,4 D

various 2,4-DP

Benzoic acidsTrade Name Common Name Trade Name Common Name Trade Name Common NameBanvel dicamba Vanquish dicamba

Pyridine acidsTrade Name Common Name Trade Name Common Name Trade Name Common NameMilestonePathfinderTurflon ester

aminopyralidtriclopyrtriclopyr

TordonSurmountLontrel

piclorampicloramclopyralid

TranslineSpotlightVista

clopyralidfluoxypyrfluoxypyr

' III. PHOTOSYNTHESIS INHIBITORS (Inhibit electron transport in Photosystem II)Trade Name Common Name Trade Name Common Name Trade Name Common NameAatrexAtrazinePrincepSpike

atrazineatrazinesimazinetebuthiuron

SencorVelparPramitolHyvar

metribuzinhexazinoneprometonbromacil

KarmexDirexLoroxSinbar

diurondiuronlinuronterbacil

' IV. CELL MEMBRANE DISRUPTERS (Cause cell membranes to rupture by various means)Trade Name Common Name Trade Name Common Name Trade Name Common NameGramoxoneReward

paraquatdiquat

FinaleGoal

glufosinateoxyflurofen

SureGuardQuick Silver

flumioxazincarfentrazone

' V. LIPID SYNTHESIS INHIBITORS (ACCASE INHIBITORS)Trade Name Common Name Trade Name Common Name Trade Name Common NameEnvoySelect

clethodimclethodim

VantagePoast

sethoxydimsethoxydim

FusiladeOrnamec

Fluazyprop-butylFluazyprop-butyl

© 2006 PESTICIDE TRAINING RESOURCES102706

' VI. SEEDLING GROWTH INHIBITORSRoot Inhibitors (Dinitroanalines)Trade Name Common Name Trade Name Common Name Trade Name Common NameCavalcadeBarricadeEndurance

prodiamineprodiamineprodiamine

PendulumPendimaxTreflan

pendimethalinpendimethalintrifluralin

SurflanRoutBalan

oryzalinoryzalinbenefin

Shoot Inhibitors (Chloroacetamides)Trade Name Common Name Trade Name Common Name Trade Name Common NamePennant metolachlor Eptan EPTC Preen Groundcover EPTC

Root & Shoot InhibitorsTrade Name Common Name Trade Name Common Name Trade Name Common NameBetasan bensulide Prefar bensulide Dimension dithiopyr

Injury SymptomsI. AMINO ACID SYNTHESIS INHIBITORS Sulfonylureas & Imidazolinones (Inhibitors of acetolactase synthase (ALS)): These herbicides can be broad spectrum or veryselective depending on the compound. Most have foliar and root uptake. Symptoms can be slow to develop: days to weeks afterapplication. Shoot Symptoms: Chlorosis (yellowing) and stunting of new growth. Leaf symptoms: Inter-veinal (between veins)chlorosis, deformed leaves, purpling or reddening of veins in leaves followed by necrosis (death) of leaves and stems. Sublethalconcentrations of herbicide may cause a proliferation of shoot growth and shortening of internodes. Root symptoms: proliferationof growth of secondary roots, giving a ?bottle brush” appearance.

II. GROWTH REGULATORSSymptoms on Dicots: Symptoms evident on new growth first. All or some of the following symptoms. Yellowing of foliage,stoppage of growth. Leaf malformations: parallel veination, puckering, leaf crinkle, leaf cupping, leaf strapping. Twisting of stemsand petioles. Root formation on stems. Symptoms on Monocots: rolled leaves, leaning stems, brittle stems. Deformed florets,diminished seed production.

III. PHOTOSYNTHESIS INHIBITORSSymptoms from soil applied Photosynthesis Inhibitors: Susceptible grasses become chlorotic (yellow) and necrosis (death) oftissue begins at the leaf tips and progresses downward. Susceptible broadleafs exhibit intra-veinal(within) or inter-veinal (between)chlorosis (yellowing) with death of tissues beginning at the leaf margins and progressing toward the center. Symptoms on monocotsand dicots usually appears first on older foliage then progresses to newer foliage. Symptoms from foliar applied PhotosynthesisInhibitors: yellowing, general leaf burn. Symptoms on plants usually appearing much faster than symptoms from soil appliedPhotosynthesis Inhibitors.

IV. CELL MEMBRANE DISRUPTERSSymptoms on plant tissue first appear as water soaked, followed by necrosis (brown and dead). Drift injury will appear as dead spotson leaves. Plants treated with Glufosinate: yellowing is the first symptom, then necrosis 2-4 days later.

V. LIPID SYNTHESIS INHIBITORS These herbicides are selective grass herbicides. Symptoms on grasses are: yellowing, plus or minus reddening/pink coloring offoliage. New leaves in whorls pull out easily and reveal death of tissues at the base of leaves.

VI. SEEDLING GROWTH INHIBITORSRoot Inhibitors (Dinitroanalines): Symptoms on monocots: short swollen shoots (coleoptiles) after emergence. Affected dicotshave swollen stems(hypocotyls) below the cotyledon leaves. Both monocots and dicots have roots which are short, stubby, often clubshaped and brittle: symptoms are similar to damage caused by chloroacetamide herbicides.

Shoot Inhibitors (Chloroacetamides): Symptoms on Monocots: failure of shoots to emerge from soil and/or failure of shoots toemerge from the whorl (coleoptile). Symptoms on Dicots: Enlarged cotyledons, restricted growth of true leaves, dark green foliage,leaf crinkle, cupping and twisting. Roots may become short, thick, brittle: root symptoms very similar to root damage caused bydinitroanaline herbicides.

Root & Shoot Inhibitors: Symptoms similar to damage caused by Shoot Inhibitors. Symptoms on Monocots: failure of shoots toemerge from soil and/or failure of shoots to emerge from the whorl (coleoptile). Symptoms on dicots: general stunting, often witha drawstring appearance around the margin of true leaves.

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