Herbicide Modes of Action

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Herbicide Modes of Action

• Eric P. Prostko
• Extension Weed Specialist
• Department of Crop Soil Sciences
• The University of Georgia

April 2008
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Some things to remember.

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

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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

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Mechanism of Action (Site)

• Location at which a herbicide exerts its toxicity
  at the cellular level
• more specific

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ACCase Inhibitors

• Inhibit acetyl-CoA-carboxylase (ACCase) enzyme
• Enzyme needed for fatty acid synthesis
• Dims and Fops
• Achieve, Assure, Axial, Fusilade, Poast, Select

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rotted meristem
Source W. K. Vencill, UGA
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ALS Inhibitors

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

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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

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Cadre yellow flash
Staple on Sorghum
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Resolve 25WG (rimsulfuron) Injury to Field Corn
Pictures _at_ 18 DAT
1.0 oz/A Applied PRE
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Photosystem II Inhibitors

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

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Bladex
Cotoran
Source W. K. Vencill, UGA
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Photosystem I Inhibitors

• Accept electrons from PSI to form radicals
• Super radicals formed to create peroxides
• Diquat, paraquat

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Paraquat
Source Purdue University
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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

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Valor Injury on Peanut
Blazer Injury on Peanut
Cobra on Soybeans
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Carotenoid Biosynthesis Inhibitors

• Inhibit phytoene desaturase (PDS) or
  hydroxyphenyl pyruvate dioxygenase (HPPD)
• Command, Callisto, Laudis, Solicam/Zorial, Impact

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Command
Zorial
Laudis
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EPSP Synthase Inhibitor

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

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Source Purdue University Weed Science
Source MSU Weed Science
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Glutamine Synthetase Inhibitors

• Glutamine synthetase converts glutamate and
  ammonia to glutamine
• Causes ammonia accumulation in plants
• Liberty, Ignite

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Source University of Missouri Weed Science
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Mitosis Inhibitors

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

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Prowl Injury on Corn
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Dual Injury
Source University of Wisconsin Weed Science
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Fatty Acid and Lipid Biosynthesis Inhibitors

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

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Source Purdue University Weed Science
Source UC-Davis Weed Science
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Synthetic Auxins

• Disrupt hormonal balance
• 2,4-D, Banvel, Clarity, Status, Stinger, MCPA,
  Facet, Remedy, Grazon PD

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Source Purdue University Weed Science
Source Purdue University Weed Science
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Unknown MOA

• DSMA, MSMA
• Cell membrane destruction???

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MSMA on Peanut
MSMA on Zoysia
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UGA Weed Science www.gaweed.com