SLIDE 1
Classification can be based on:
- 1. Chemical structure or family
2-choro-N-[[(4-methoxy-6-methyl-1,3,5- triazin-2-yl)amino]carbonyl]benzenesulfonamide
- 2. Cropping system or ecosystem
- 3. Mode of action
Herbicide Classification and Mode of Action William E. Dyer - - PowerPoint PPT Presentation
Herbicide Classification and Mode of Action William E. Dyer - - PowerPoint PPT Presentation
Herbicide Classification and Mode of Action William E. Dyer Department of Plant Sciences wdyer@montana.edu Classification can be based on: 1. Chemical structure or family 2-choro-N-[[(4-methoxy-6-methyl-1,3,5-
SLIDE 2
SLIDE 3
Why Know Herbicide Modes of Action?
- Better understanding of how herbicides
perform
- Improve herbicide performance
- Diagnose herbicide injury
- Prevent and manage herbicide resistance
SLIDE 4
Contact Absorption Toxicity Movement Site of Action
Herbicide Mode of Action
SLIDE 5
Site of Absorption and Translocation
Foliar Contact
(Gramoxone)
Root Contact
(Treflan)
Phloem
(Roundup)
Xylem
(Spike)
Xylem and Phloem
(Banvel, Tordon)
Rangeland herbicides
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Herbicide Classification
- Selectivity -
- Selective: controls or suppresses one
species of plant without seriously affecting the growth of another plant species
– 2,4-D
- Nonselective: control plants regardless of
species
– Roundup
SLIDE 7
Some Things to Remember….
- Photosynthesis (food)
- Pigments (energy/light capture)
- Respiration (energy)
- Amino acids (proteins/growth)
- Lipids (cell membranes)
- Hormones (auxin and others)
SLIDE 8
Classification by Mode of Action Group
1) Lipid Biosynthesis Inhibitors 2) Amino Acid Biosynthesis Inhibitors 3) Cell Division Inhibitors 4) Synthetic Auxins 5,6,7) Photosynthesis Inhibitors 9) EPSP Synthase Inhibitor 14) Pigment Inhibitors 22) Membrane Disruptors 16,17,26) Unknown
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Herbicide Mode of Action Groups
Group 1: Lipid synthesis inhibitors (“grass killers”) Block ACCase enzyme Trade Names: Hoelon, Fusilade, Poast, Axial, Puma, Assure Symptoms Mechanism of resistance: Altered target site
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Altered target site
The normal situation A resistant enzyme
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Herbicide Mode of Action Groups
Group 2: Amino acid synthesis inhibitors; blocks ALS enzyme Trade names: Glean, Telar, Finesse, Muster, Permit, Ally,
Escort, Canvas, Finesse, Accent, Basis, Beacon, Exceed, Peak, Matrix, Oust, Maverick, Harmony, Pinnacle, Cheyenne, Reliance, Amber, Rave, Upbeet, Arsenal, Assert, Lightning, Motive, Plateau, Pursuit, Raptor, Sceptor, Broadstrike, FirstRate, StrongArm, Python
Mechanism of Resistance: altered target site
- Translocates to new growth in xylem and phloem
- Plants stop growing shortly after application, but plant death
may be slow (10+ days)
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Plateau Injury Symptoms
Chlorosis of youngest tissue Stunting Chlorosis of youngest tissue
ALS Inhibitor Symptoms
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Herbicide Mode of Action Groups
Group 4: Synthetic auxins Overwhelm natural auxin pathways Trade names: 2,4-D, MCPA, Banvel, Clarity, Milestone,
Perspective, Tordon, Stinger, Curtail, Transline, Starane, Garlon, Remedy, Renovate, Paramount, Drive
Mechanism of Resistance: ???
- Translocates in both xylem and phloem
- Symptoms most obvious in new growth
- Selectively kill broadleaf plants
- Soil residue varies from a few days to several years
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Synthetic Auxin Symptoms
Phenoxy on Red Oak
University of Illinois extension
Phenoxy drift on tomato
Ohio State University
Benzoic acid on soybean
Photo: HMOA and Crop Injury Symptoms
- Univ. of Minnesota Extension
Washington State University Extension
Pyrdine on tomato
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Synthetic Auxin Symptoms
Twisting needles due to drift of triclopyr
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Herbicide Mode of Action Groups
Groups 5,6,7: Photosystem II inhibitors Block photosynthesis Trade names: Aatrex, Princep, Simazine, Velpar,
Sencor, Hyvar X, Sinbar, Basagran, Buctril, Bronate, Karmex, Direx, Lorox, Linex, Spike
Mechanism of Resistance: altered target site
- Injures old growth first, moves only upward in xylem
- Injury symptoms: yellowing (chlorosis) of leaf tissue
followed by death (necrosis) of the tissue
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Injury from PSII herbicide
Interveinal, tip, and margin chlorosis Interveinal chlorosis Leaves necrotic
SLIDE 18
Consequences of photosynthetic inhibition
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Herbicide Mode of Action Groups
Group 9: Glycines (glyphosate) Inhibit amino acid biosynthesis Trade names: Roundup, Gallup, Kleenup, Landmaster,
Pondmaster, Ranger, Rodeo, Touchdown
Mechanism of Resistance: reduced translocation, gene amplification
- Translocates to new growth in xylem and phloem
- Plants stop growing shortly after application, but plant
death may be slow (10+ days)
SLIDE 20
chlorosis shortened internodes stem proliferation
Glyphosate Injury Symptoms
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Herbicide Mode of Action Groups
Group 22: Bipyridiliums (paraquat) Divert electrons from photosynthesis Trade names: Reglone, Gramoxone, Scythe, many others Mechanism of Resistance: enhanced detoxification Symptoms
SLIDE 22
Other Herbicide Mode of Action Families
Groups 16,17,26: Unknown Group 3: Microtubule assembly inhibitors Group 14: Protox inhibitors Group 15: Long chain fatty acid synthesis inhibitors
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Why aren’t there any new herbicides?
- Half of all current herbicides inhibit one of
- nly three target enzymes.
- All herbicides now on the market
were discovered by accident.
- New ‘target-based’
technologies MAY lead to new herbicides.
R S R
Banvel-resistant kochia
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