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Herbicide Mode of Action
Herbicide Mode of Action
How a herbicide worksUse herbicides more efficiently
Recognize and diagnose injury problems
Herbicide resistance management
Herbicide –Plant Interactions
Absorption
Translocation
Metabolism
Mechanism of Action
Physiological response
Requirements for Herbicide Activity
Contact with the target weed
Absorption into the plant
Accumulation of toxic levels at the site of action
Herbicide Selectivity
Differential response of plant species to a herbicide
Selective
Nonselective
Herbicide SelectivityApplication RateHerbicide PlacementSpray RetentionDifferential AbsorptionDifferential TranslocationMetabolismAltered Site of Action (Herbicide Resistance)
Absorption of Soil-Applied Herbicides
Roots
Shoots
Absorption of PostemergenceHerbicides
Leaf surface coverageLeaf surface propertiesHerbicide-spray propertiesTemperatureHumidityPlant Vigor
Herbicide MetabolismChemical transformations of a herbicide in a plantMetabolism generally results in detoxification of a herbicide, but also can increase the toxicity of a herbicide
Altered Site of ActionInability of a herbicide to bind to the site of action due to a genetic and conformational difference at the binding site compared to susceptible biotypes.
Herbicide Resistance
Modified Site of Action
Triazine Resistant Palmer Amaranth
Herbicide Cross ResistanceWeed resistance to different herbicides that have the same mode of action.ALS herbicides
SulfonylureasImidazolinonesTriazolopyrimidines
ALS Cross Resistant Cocklebur
Herbicide Multiple Resistance
Weed biotypes with resistance to herbicides having different modes of action.Examples: kochia and pigweeds that are resistant to both triazine and ALS inhibiting herbicides.
ALS & Triazine Resistant Waterhemp
Herbicide Translocation
Movement of the herbicide inside the plant
Contact herbicides: not translocated
Systemic herbicides: translocatedPhloem translocated
Xylem translocated
Herbicide TranslocationPhloem Translocated:RoundupPoast
Foliar Contact: ParaquatCobraBuctrilBasagran
Xylem Translocated:
Phloem & XylemTranslocated:
2,4-DBanvelTordonGleanPursuit
XylemPhloem
Atrazine, Command, Balance
Contact vs. Systemic Herbicides
Timing Effects on Annual Weed Control
Emergence Seedling Vegetative Flowering MaturityGrowth Stage
Wee
d C
ontr
ol
Timing Effects on Perennial Weed Control
Dormancy Vegetative Bud Flowering Maturity Fall
Growth Stage
Wee
d C
ontr
ol
Herbicide Mechanisms of ActionPlant Growth RegulatorsSeedling Growth InhibitorsPhotosynthetic InhibitorsCell Membrane DisruptorsAmino Acid Synthesis InhibitorsLipid Synthesis InhibitorsNitrogen Metabolism InhibitorsPigment Inhibitors
Plant Growth RegulatorsPhenoxies: 2,4-D, MCPA,
2,4-DB , etc.Benzoic Acids: Banvel, Clarity, DistinctPyridines: Tordon, Remedy,
Crossbow, Stinger, Starane
Quinolines: Paramount
Puckered Soybean leaves from Tordon
Tordon Runoff into Soybean Field
2,4-D on Grain Sorghum
2,4-D Damage to Corn Brace Roots
Fall applied 2,4-D on Wheat
Late Application of Banvel + 2,4-D on Wheat
Late Application of Paramount on Giant Foxtail
Growth Regulator Use Concerns
Drift and injury to nontarget plants
Carryover: Tordon
Groundwater Contamination: Tordon
Seedling Growth Inhibitors
Thiocarbamates: Sutan, Eradicane, Eptam, Fargo
Acetanilides: Lasso, Partner, Dual Magnum, Outlook,
Harness, Surpass, Axiom, Ramrod
Dinitroanilines: Treflan, Prowl, Balan, Sonalan
Acetamides(Lasso, Dual, Outlook, Harness, Surpass, Define, Ramrod)
Applied preemergence or with shallow incorporationDisrupts cell development in emerging shoot (coleoptile) during germination and emergence
Acetamide Injury to Soybeans
Acetamide Injury to Grain Sorghum
Safened and Unsafened Sorghum treated with Dual
Dinitroanalines(Treflan, Prowl, Balan, Sonalan)
Generally incorporated to mix the herbicide into the soil and reduce photodecomposition and volatility losses
Inhibits cell division (mitosis)
Active on emerging shoot and the root tips
Treflan Damage to Corn Roots
Swollen hypocotyls and Poor Root Development from Treflan
Brittle Stems and Lodging from Prowl Damage
Photosynthetic InhibitorsTriazines: Atrazine, Sencor, Lexone,
Bladex, Princep, VelparPhenylureas: Lorox, Karmex, SpikeUracils: Sinbar, HyvarNitriles: BuctrilPyridazines: ToughBenzothiadiazones: Basagran
Atrazine Carryover on Wheat
Triazine Injury to Soybeans
Cell Membrane Disruptors
Photosystem I Inhibitors:Dipyridiliums - Gramoxone Extra, Diquat
PPO Inhibitors:
Diphenylethers - Blazer, Cobra, Flexstar
Triazolinones - Aim, Authority, Spartan
Phenylthalimides - Resource
Cell Membrane Disruptors(Paraquat, Cobra, Blazer, Authority)
Contact herbicides - thorough spray coverage and small weeds essential for good weed control
Light activated herbicides that quickly destroy cell membranes, resulting in “leaf burn” type symptom
Cobra Burn on Soybeans
Rapid Burn Activity of Cobra
Aim Injury on Sorghum Leaves
Amino Acid Synthesis InhibitorsALS inhibitors
Sulfonylureas: Glean, Amber, Ally, PeakFinesse, Classic, Pinnacle,
Synchrony STS, Accent, Beacon, Exceed, Permit
Imidazolinones: Scepter, Pursuit, Lightning, Raptor
Triazolopyrimidines: Broadstrike, Python, FirstRate
ESPS inhibitors:Roundup, Touchdown
ALS Inhibitors(Glean, Peak, Accent, Pursuit, Python, etc.)
Absorbed through both roots and shoots and readily
translocated in both xylem and phloem
Inhibits the Acetolactate Synthase (ALS) enzyme
responsible for the production of branched chain amino
acids valine, leucine, and isoleucine
Quick development of herbicide resistance
Chlorosis of New Growth from Glean on Tansy Mustard
ALS Injury to Soybeans
Peak Carryover Injury to Soybeans
Basis Injury to Corn Following Cold Weather
Bottle-brushing of Roots from ALS herbicide Carryover on Corn
EPSP Inhibitors(Glyphosate)
Tightly adsorbed and inactive in soil
Phloem translocated
Inhibits EPSP enzyme responsible for production of aromatic amino acids phenylalinine, tyrosine and tryptophan
Very nontoxic
Gradual Death from Roundup Treatment
Genetically Engineered Roundup Ready Corn
Roundup Drift Damage to Corn
Chlorotic Roundup Ready Soybeans from Late Treatment
Nitrogen Metabolism Inhibitor(Liberty, Ignite 280)
Inhibits glutamine synthetase enzyme involved with nitrogen metabolism
Limited translocation
No soil activity
Non Liberty Link Corn Treated with Liberty
Lipid Synthesis Inhibitors
Postemergence grass control herbicides
Cyclohexanediones (Dims):Poast, Poast Plus, Select
Aryloxyphenoxypropionates (Fops):Assure, Fusilade, Fusion, Option
Corn Treated with Poast Plus
“Rotten Neck” symptom from Post Grass Herbicides
Drift Damage on Corn from Post Grass Herbicide
Drought Stress Effect on Poast Herbicide Activity
Pigment Inhibitors(Command, Balance, Callisto,
Impact, Laudis, Huskie)Absorbed through roots and shoots, but translocated only in the xylemPrevents synthesis of pigments that protect chlorophylFoliage turns white and appears bleached
Bleached Crabgrass from Balance Treatment
Balance Injury to Corn with Cold Wet Conditions
Command Carryover Injury to Double Cropped Wheat
Command Carryover Injury to Oats
K StateResearch and Extension