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Herbicide Modes of Action

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

2 Some things to remember….
photosynthesis (food) respiration (energy) amino acids (proteins/growth) lipids (cell membranes) pigments (energy/light capture) chlorophyll, carotenoids mitosis (cell division)

3 Mode of Action the sequence of events that leads to plant death or growth interruption 2 phases * movement to target site * interaction at target site

4 Mechanism of Action (Site)
Location at which a herbicide exerts its toxicity at the cellular level more specific

5 ACCase Inhibitors Inhibit acetyl-CoA-carboxylase (ACCase) enzyme
Enzyme needed for fatty acid synthesis Dim’s and Fop’s Achieve, Assure, Axial, Fusilade, Poast, Select

6 “rotted” meristem Source: W. K. Vencill, UGA

7 ALS Inhibitors Inhibit acetolactate synthase (ALS) enzyme
enzyme needed to produce certain amino acids (isoleucine, leucine, valine)

8 Commonly Used ALS Herbicides
Accent Ally/Cimarron Beacon Beyond Cadre Classic Envoke Exceed Express Finesse FirstRate Glean Harmony Extra Maverick Pro Osprey Peak Permit Pursuit Python Scepter Staple Strongarm

9 Cadre “yellow flash” Staple+ on Sorghum

10 Resolve 25WG (rimsulfuron) Injury to Field Corn
18 DAT 1.0 oz/A Applied PRE

11 Photosystem II Inhibitors
Inhibit photosynthesis by binding to QB-binding niche on D1 protein Evik, Caparol, Atrazine, Basagran, Buctril, Direx, Cotoron, Lorox, Sencor, Simazine

12 Bladex Cotoran Source: W. K. Vencill, UGA

13 Photosystem I Inhibitors
Accept electrons from PSI to form radicals Super radicals formed to create peroxides Diquat, paraquat

14 Paraquat Source: Purdue University

15 PPO Inhibiting Herbicides
PPO or Protox Protoporphyrinogen oxidase Enzyme found in chloroplast and mitochondria needed for formation of chlorophyll Cell membrane destruction Many common herbicides have this mode of action!! Ultra Blazer, Cobra, Goal, Reflex, Ronstar, Resource, Aim, Valor, Storm, Spartan, ET

16 Blazer Injury on Peanut
Valor Injury on Peanut Blazer Injury on Peanut Cobra on Soybeans

17 Carotenoid Biosynthesis Inhibitors
Inhibit phytoene desaturase (PDS) or hydroxyphenyl pyruvate dioxygenase (HPPD) Command, Callisto, Laudis, Solicam/Zorial, Impact

18 Command Zorial Laudis

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

20 Source: Purdue University Weed Science
Source: MSU Weed Science

21 Glutamine Synthetase Inhibitors
Glutamine synthetase converts glutamate and ammonia to glutamine Causes ammonia accumulation in plants Liberty, Ignite

22 Source: University of Missouri Weed Science

23 Mitosis Inhibitors Microtubule inhibition
Treflan, Prowl, Sonalan, Surflan, Dacthal Inhibition of very long-chain fatty acids Dual Magnum, Outlook, Intrro

24 Prowl Injury on Corn

25 Dual Injury Source: University of Wisconsin Weed Science

26 Fatty Acid and Lipid Biosynthesis Inhibitors
Inhibition of lipid synthesis (not ACCase) Prefar, Sutan, Eptam, Eradicane, Ordram, Tillam, Bolero

27 Source: Purdue University Weed Science
Source: UC-Davis Weed Science

28 Synthetic Auxins Disrupt hormonal balance
2,4-D, Banvel, Clarity, Status, Stinger, MCPA, Facet, Remedy, Grazon P+D

29 Source: Purdue University Weed Science

30 Unknown MOA DSMA, MSMA Cell membrane destruction???

31 MSMA on Peanut MSMA on Zoysia

32 UGA Weed Science

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