Herbicide Mode of Action
How many ways (modes of action) do herbicides kill weeds? A. B. C. D.
Tri River Pest Management Workshop February 15th, 201...
Herbicide Mode of Action and Symptoms Plant Growth Regulators
Herbicide Mode of Action and Symptomology: Light-Activated Herbicides (Photosystem II)
Light Activated Herbicides Share a Common MOA Lipid peroxidation Production of reactive oxygen, hydroxyl radicals Membrane leakage and cell death, usually starting with the chloroplast
Photosystem II Injury younger leaves show less injury interveinal chlorosis
burning of leaf margin
PGR Mode of Action Mode of action we understand symptoms we don’t understand why grasses are resistant and broadleaf plants are susceptible differences in metabolism?
Canada thistle response to Milestone 7 DAT
Herbicides that Mimic Natural Plant HormonesHormones-PGR Natural plant hormones control growth, development tissue differentiation RNA and DNA synthesis
Herbicides with this mode of action can do the same things at low concentrations At high concentrations these compounds are herbicides
PGR Mode of Action Symptoms abnormal growth resulting in twisted stems stem swelling due to rapid and uncontrolled cell division differentiated cells changing to immature cells
Canada thistle response to Milestone 14 DAT
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Common Leaf Symptoms from PGR Exposure
Root Absorption of PGR Herbicides
translocation to growing point normal swollen hypocotyl callus formation on roots lack of root development
cupped and blistered from PGR exposure
Amino Acid Inhibitors Herbicide Mode of Action and Symptoms Amino Acid Inhibitors
Very important group of herbicides ALS inhibitors First sulfonylurea introduced in 1979 by DuPont (Telar) First imidazolinone introduced in 1981 by American Cyanamid (Arsenal/Habitat)
EPSP synthase inhibitor Roundup introduced 1971
General Characteristics of Amino Acid Inhibitors Excellent foliar and root absorption Broad weed spectrum Translocation to shoot and root meristems Plants stop growing shortly after application Plant death can take 7 to 10 days Resistance has developed
Important Terminology Sulfonylurea (SU) herbicide Telar, Escort
Imidazolinone (IMI) herbicides Plateau, Habitat
These chemical families inhibit branch chain amino acid production-acetolactate synthase or ALS
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A) SU (Telar) binding to channel leading to ALS active site. Notice that herbicide is deeper active site then IMI molecule. Also interacts with more amino acids.
B) IMI (Plateau) binding to channel leading to ALS active site. Notice that herbicide is closer to the surface site then SU molecule. Also interacts with fewer amino acids.
Plateau injury symptoms expressed by leafy spurge
Roundup (glyphosate) Inhibits the production of aromatic amino acids Competitive with PEP for the enzyme 5enolpyruvylshikimate-3-phosphate synthase or EPSP synthase. Non-selective, no soil activity Monsanto has developed Roundup Ready corn, soybeans, sugar beets, alfalfa, cotton, rice.
•Structurally similar •Glyphosate dissociation from EPSPS is 2300 times slower than PEP!
