Herbicide Modes of Action Herbicide Modes of Action Eric P. Prostko Eric P. Prostko Extension Weed Specialist Extension Weed Specialist Department of Crop & Soil Sciences Department of Crop & Soil Sciences The University of Georgia The 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, carotenoids • chlorophyll, carotenoids � mitosis mitosis (cell division) (cell division) �
Mode of Action Mode of Action � the sequence of events that leads to the sequence of events that leads to � plant death or growth interruption plant death or growth interruption � 2 phases 2 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 level its toxicity at the cellular level � more specific more specific �
ACCase Inhibitors ACCase Inhibitors � Inhibit acetyl Inhibit acetyl- -CoA CoA- -carboxylase carboxylase � (ACCase) enzyme (ACCase) enzyme � Enzyme needed for fatty acid Enzyme needed for fatty acid � synthesis synthesis � Dim’s and Fop’s Dim’s and Fop’s � � Achieve, Assure, Axial, Fusilade, Achieve, Assure, Axial, Fusilade, � Poast, Select Poast, Select
“rotted” meristem Source: W. K. Vencill, UGA
ALS Inhibitors ALS Inhibitors � Inhibit acetolactate synthase (ALS) Inhibit acetolactate synthase (ALS) � enzyme enzyme � enzyme needed to produce certain enzyme needed to produce certain � amino acids (isoleucine, leucine, amino acids (isoleucine, leucine, valine) valine)
Commonly Used ALS Herbicides Commonly Used ALS Herbicides � � � � Accent Accent Glean Glean � Ally/Cimarron � Ally/Cimarron � Harmony Extra � Harmony Extra � Beacon � Beacon � Maverick Pro � Maverick Pro � Beyond � Beyond � Osprey � Osprey � Cadre � Cadre � Peak � Peak � Classic � Classic � Permit � Permit � Envoke � Envoke � Pursuit � Pursuit � Exceed � Exceed � Python � Python � Express � Express � Scepter � Scepter � Finesse � Finesse � Staple � Staple � FirstRate � FirstRate � Strongarm � Strongarm
Cadre “yellow flash” Cadre “yellow flash” Staple+ on Sorghum Staple+ on Sorghum
Resolve 25WG (rimsulfuron) Injury Resolve 25WG (rimsulfuron) Injury to Field Corn to Field Corn Pictures @ 18 DAT 1.0 oz/A Applied PRE
Photosystem II Inhibitors Photosystem II Inhibitors � Inhibit photosynthesis by binding to Inhibit photosynthesis by binding to � Q B -binding niche on D1 protein binding niche on D1 protein Q B - � Evik, Caparol, Atrazine, Basagran, Evik, Caparol, Atrazine, Basagran, � Buctril, Direx, Cotoron, Lorox, Buctril, Direx, Cotoron, Lorox, Sencor, Simazine Sencor, Simazine
Bladex Bladex Cotoran Source: W. K. Vencill, UGA
Photosystem I Inhibitors Photosystem I Inhibitors � Accept electrons from PSI to form Accept electrons from PSI to form � radicals radicals � Super radicals formed to create Super radicals formed to create � peroxides peroxides � Diquat, paraquat Diquat, paraquat �
Paraquat Paraquat Source: Purdue University
PPO Inhibiting Herbicides PPO Inhibiting Herbicides � PPO or Protox PPO or Protox � • Protoporphyrinogen Protoporphyrinogen • oxidase oxidase • Enzyme found in Enzyme found in • chloroplast and chloroplast and mitochondria needed for mitochondria needed for formation of chlorophyll formation of chlorophyll • Cell membrane • Cell membrane destruction destruction � Many common herbicides Many common herbicides � have this mode of action!! have this mode of action!! , Ultra Blazer, Cobra, Goal , • • Ultra Blazer, Cobra, Goal Reflex, Ronstar, Resource, Reflex, Ronstar, Resource, Aim, Valor, Storm, Spartan, Aim, Valor, Storm, Spartan, ET ET
Valor Injury on Peanut Valor Injury on Peanut Blazer Injury on Peanut Blazer Injury on Peanut Cobra on Soybeans
Carotenoid Biosynthesis Inhibitors Carotenoid 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, Impact Solicam/Zorial, Impact
Command Zorial Zorial Laudis
EPSP Synthase Inhibitor EPSP 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) � glyphosate glyphosate �
Source: Purdue University Weed Science Source: MSU Weed Science
Glutamine Synthetase Inhibitors Glutamine Synthetase Inhibitors � Glutamine synthetase converts Glutamine synthetase converts � glutamate and ammonia to glutamate and ammonia to glutamine glutamine � Causes ammonia accumulation in Causes ammonia accumulation in � plants plants � Liberty, Ignite Liberty, Ignite �
Source: University of Missouri Weed Science
Mitosis Inhibitors Mitosis Inhibitors � Microtubule inhibition Microtubule inhibition � • Treflan, Prowl, Sonalan, Surflan, • Treflan, Prowl, Sonalan, Surflan, Dacthal Dacthal � Inhibition of very long Inhibition of very long- -chain fatty chain fatty � acids acids • Dual Magnum, Outlook, Intrro
Prowl Injury on Corn
Dual Injury Source: University of Wisconsin Weed Science
Fatty Acid and Lipid Biosynthesis Fatty Acid and Lipid Biosynthesis Inhibitors Inhibitors � Inhibition of lipid synthesis (not Inhibition of lipid synthesis (not � ACCase) ACCase) • Prefar, Sutan, Eptam, Eradicane, • Prefar, Sutan, Eptam, Eradicane, Ordram, Tillam, Bolero Ordram, Tillam, Bolero
Source: Purdue University Weed Science Source: UC-Davis Weed Science
Synthetic Auxins Synthetic Auxins � Disrupt hormonal balance Disrupt hormonal balance � � 2,4 2,4- -D, Banvel, Clarity, Status, D, Banvel, Clarity, Status, � Stinger, MCPA, Facet, Remedy, Stinger, MCPA, Facet, Remedy, Grazon P+D Grazon P+D
Source: Purdue University Weed Science Source: Purdue University Weed Science
Unknown MOA Unknown MOA � DSMA, MSMA DSMA, MSMA � � Cell membrane destruction??? Cell membrane destruction??? �
MSMA on Peanut MSMA on Zoysia
UGA Weed Science UGA Weed Science www.gaweed.com www.gaweed.com
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