Download Herbicide Classification and Mode of Action

Herbicide Classification
and Mode of Action
William E. Dyer
Department of Plant Sciences
[email protected]
Classification can be based on:
1. Chemical structure or family
2-choro-N-[[(4-methoxy-6-methyl-1,3,5triazin-2-yl)amino]carbonyl]benzenesulfonamide
2. Cropping system or ecosystem
3. Mode of action
= the plant process or pathway inhibited
by the herbicide
Why Know Herbicide Modes of
Action?
• Better understanding of how herbicides
perform
• Improve herbicide performance
• Diagnose herbicide injury
• Prevent and manage herbicide resistance
Herbicide Mode of Action
Movement
Absorption
Contact
Site of
Action
Toxicity
Site of Absorption and Translocation
Phloem
(Roundup)
Rangeland
herbicides
Xylem and
Phloem
Foliar Contact
(Gramoxone)
Root Contact
(Treflan)
(Banvel, Tordon)
Xylem
(Spike)
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
Some Things to Remember….
• Photosynthesis (food)
• Pigments (energy/light capture)
• Respiration (energy)
• Amino acids (proteins/growth)
• Lipids (cell membranes)
• Hormones (auxin and others)
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
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
Altered target site
The
normal
situation
A resistant
enzyme
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
• Translocates to new growth in xylem and phloem
• Plants stop growing shortly after application, but plant death
may be slow (10+ days)
Mechanism of Resistance: altered target site
ALS Inhibitor Symptoms
Stunting
Chlorosis of
youngest
tissue
Chlorosis of
youngest tissue
Plateau Injury Symptoms
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
• 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
Mechanism of Resistance: ???
Synthetic Auxin Symptoms
Phenoxy drift on tomato
Ohio State University
Phenoxy on Red Oak
University of Illinois extension
Benzoic acid on
soybean
Photo: HMOA and Crop Injury Symptoms
Univ. of Minnesota Extension
Pyrdine on tomato
Washington State University
Extension
Synthetic Auxin Symptoms
Twisting needles due to drift of triclopyr
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
• Injures old growth first, moves only upward in xylem
• Injury symptoms: yellowing (chlorosis) of leaf tissue
followed by death (necrosis) of the tissue
Mechanism of Resistance: altered target site
Injury from PSII herbicide
Interveinal
chlorosis
Leaves
necrotic
Interveinal, tip, and
margin chlorosis
Consequences of
photosynthetic inhibition
Herbicide Mode of Action Groups
Group 9: Glycines (glyphosate)
Inhibit amino acid biosynthesis
Trade names: Roundup, Gallup, Kleenup, Landmaster,
Pondmaster, Ranger, Rodeo, Touchdown
• Translocates to new growth in xylem and phloem
• Plants stop growing shortly after application, but plant
death may be slow (10+ days)
Mechanism of Resistance: reduced
translocation, gene amplification
Glyphosate Injury Symptoms
chlorosis
shortened
internodes
stem proliferation
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
Other Herbicide Mode of Action Families
Group 3: Microtubule assembly
inhibitors
Group 14: Protox
inhibitors
Group 15: Long chain fatty acid synthesis
inhibitors
Groups 16,17,26: Unknown
Why aren’t there any new herbicides?
• All herbicides now on the market
were discovered by accident.
• Half of all current herbicides inhibit one of
only three target enzymes.
Banvel-resistant kochia
• New ‘target-based’
technologies MAY
lead to new
herbicides.
R
S
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More Information?
http://msuextension.org/publications/Ag
andNaturalResources/MT200506AG
.pdf