Herbicide Modes of Action Eric P. Prostko Extension Weed Specialist Department of Crop & Soil Sciences The University of Georgia April 2008.

Herbicide Modes of ActionHerbicide Modes of Action

Eric P. ProstkoEric P. Prostko

Extension Weed SpecialistExtension Weed Specialist

Department of Crop & Soil SciencesDepartment of Crop & Soil Sciences

The University of GeorgiaThe University of Georgia

April 2008

Some things to remember….Some things to remember….

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

• chlorophyll, carotenoidschlorophyll, carotenoids

mitosis mitosis (cell division)(cell division)

Mode of ActionMode of Action

the sequence of events that leads to the sequence of events that leads to plant death or growth interruptionplant death or growth interruption

2 phases2 phases

* movement to target site* movement to target site

* interaction at target site* interaction at target site

Mechanism of Action (Site)Mechanism of Action (Site)

Location at which a herbicide exerts Location at which a herbicide exerts its toxicity at the cellular levelits toxicity at the cellular level

more specificmore specific

ACCase InhibitorsACCase Inhibitors

Inhibit acetyl-CoA-carboxylase Inhibit acetyl-CoA-carboxylase (ACCase) enzyme(ACCase) enzyme

Enzyme needed for fatty acid Enzyme needed for fatty acid synthesissynthesis

Dim’s and Fop’sDim’s and Fop’s Achieve, Assure, Axial, Fusilade, Achieve, Assure, Axial, Fusilade,

Poast, Select Poast, Select

Source: W. K. Vencill, UGA

“rotted” meristem

ALS InhibitorsALS Inhibitors

Inhibit acetolactate synthase (ALS) Inhibit acetolactate synthase (ALS) enzymeenzyme

enzyme needed to produce certain enzyme needed to produce certain amino acids (isoleucine, leucine, amino acids (isoleucine, leucine, valine)valine)

Commonly Used ALS HerbicidesCommonly Used ALS Herbicides

AccentAccent Ally/CimarronAlly/Cimarron BeaconBeacon BeyondBeyond Cadre Cadre ClassicClassic EnvokeEnvoke ExceedExceed Express Express FinesseFinesse FirstRateFirstRate

GleanGlean Harmony ExtraHarmony Extra Maverick ProMaverick Pro Osprey Osprey PeakPeak PermitPermit PursuitPursuit PythonPython ScepterScepter StapleStaple Strongarm Strongarm

Cadre “yellow flash”Cadre “yellow flash”

Staple+ on SorghumStaple+ on Sorghum

Resolve 25WG (rimsulfuron) Injury Resolve 25WG (rimsulfuron) Injury to Field Cornto Field Corn

Pictures @ 18 DAT 1.0 oz/A Applied PRE

Photosystem II InhibitorsPhotosystem II Inhibitors

Inhibit photosynthesis by binding to Inhibit photosynthesis by binding to QQBB-binding niche on D1 protein-binding niche on D1 protein

Evik, Caparol, Atrazine, Basagran, Evik, Caparol, Atrazine, Basagran, Buctril, Direx, Cotoron, Lorox, Buctril, Direx, Cotoron, Lorox, Sencor, SimazineSencor, Simazine

BladexBladexCotoran

Source: W. K. Vencill, UGA

Photosystem I InhibitorsPhotosystem I Inhibitors

Accept electrons from PSI to form Accept electrons from PSI to form radicalsradicals

Super radicals formed to create Super radicals formed to create peroxidesperoxides

Diquat, paraquatDiquat, paraquat

ParaquatParaquat

Source: Purdue University

PPO Inhibiting HerbicidesPPO Inhibiting Herbicides

PPO or ProtoxPPO or Protox• Protoporphyrinogen Protoporphyrinogen

oxidaseoxidase• Enzyme found in Enzyme found in

chloroplast and chloroplast and mitochondria needed for mitochondria needed for formation of chlorophyllformation of chlorophyll

• Cell membrane Cell membrane destructiondestruction

Many common herbicides Many common herbicides have this mode of action!!have this mode of action!!• Ultra Blazer, Cobra, GoalUltra Blazer, Cobra, Goal, ,

Reflex, Ronstar, Resource, Reflex, Ronstar, Resource, Aim, Valor, Storm, Spartan, Aim, Valor, Storm, Spartan, ETET

Blazer Injury on PeanutBlazer Injury on Peanut Valor Injury on PeanutValor Injury on Peanut

Cobra on Soybeans

Carotenoid Biosynthesis InhibitorsCarotenoid Biosynthesis Inhibitors

Inhibit phytoene desaturase (PDS) Inhibit phytoene desaturase (PDS) or hydroxyphenyl pyruvate or hydroxyphenyl pyruvate dioxygenase (HPPD)dioxygenase (HPPD)

Command, Callisto, Laudis, Command, Callisto, Laudis, Solicam/Zorial, ImpactSolicam/Zorial, Impact

Command

ZorialZorial

Laudis

EPSP Synthase InhibitorEPSP Synthase Inhibitor

EPSP synthase needed for EPSP synthase needed for production of certain amino acids production of certain amino acids (tryptophan, tyrosine, and (tryptophan, tyrosine, and phenylalanine)phenylalanine)

glyphosateglyphosate

Source: Purdue University Weed Science

Source: MSU Weed Science

Glutamine Synthetase InhibitorsGlutamine Synthetase Inhibitors

Glutamine synthetase converts Glutamine synthetase converts glutamate and ammonia to glutamate and ammonia to glutamineglutamine

Causes ammonia accumulation in Causes ammonia accumulation in plantsplants

Liberty, IgniteLiberty, Ignite

Source: University of Missouri Weed Science

Mitosis InhibitorsMitosis Inhibitors

Microtubule inhibitionMicrotubule inhibition• Treflan, Prowl, Sonalan, Surflan, Treflan, Prowl, Sonalan, Surflan,

DacthalDacthal

Inhibition of very long-chain fatty Inhibition of very long-chain fatty acidsacids• Dual Magnum, Outlook, Intrro

Prowl Injury on Corn

Source: University of Wisconsin Weed Science

Dual Injury

Fatty Acid and Lipid Biosynthesis Fatty Acid and Lipid Biosynthesis InhibitorsInhibitors

Inhibition of lipid synthesis (not Inhibition of lipid synthesis (not ACCase)ACCase)• Prefar, Sutan, Eptam, Eradicane, Prefar, Sutan, Eptam, Eradicane,

Ordram, Tillam, BoleroOrdram, Tillam, Bolero

Source: Purdue University Weed Science

Source: UC-Davis Weed Science

Synthetic AuxinsSynthetic Auxins

Disrupt hormonal balanceDisrupt hormonal balance

2,4-D, Banvel, Clarity, Status, 2,4-D, Banvel, Clarity, Status, Stinger, MCPA, Facet, Remedy, Stinger, MCPA, Facet, Remedy, Grazon P+DGrazon P+D

Source: Purdue University Weed Science

Source: Purdue University Weed Science

Unknown MOAUnknown MOA

DSMA, MSMADSMA, MSMA Cell membrane destruction???Cell membrane destruction???

MSMA on Peanut

MSMA on Zoysia

UGA Weed ScienceUGA Weed Sciencewww.gaweed.comwww.gaweed.com