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“Herbicides and Their Mechanisms of Action”
Integrated Pest Management & Certification Training
Richard D. LeeIPM Specialist
USDI-BLM
Journey in Time
1984:Cyanamid BASFMiles Eli LillyDow DuPontStauffer ShellICI Americas CIBA-GeigyMonsanto Nor-AM
Union Carbide HoechstRohm & Haas VelsicolZoecon ISK BiotechFMC Ortho20 companies20 companies
Journey in Time
Early 2002:SyngentaBayerBASFDow AgroSciencesDuPontValentMonsantoFMC
8 companies8 companies
Active Ingredients Approved for Use on BLM
Atrazine AAtrex Nine-O ® Syngenta Bromacil Hyvar ® DuPont Chlorsulfuron Telar ® DuPont Clopyralid Transline ® Dow AgroSci. 2,4-D various several Dicamba Clarity ® BASF
Vanquish ® Syngenta Diuron Karmex ® Griffin Fosamine Ammonium
Krenite ® DuPont Glyphosate Roundup Pro ® Monsanto
AquaMaster ® Monsanto Hexazinone Velpar L ® DuPont
Active Ingredients Approved for Use on BLM
Imazapyr Arsenal ® BASF Imazapic Plateau ® BASF Mefluidide Embark ® PBI Gordon Metsulfuron
methyl Escort XP ® DuPont Picloram Tordon 22K ® Dow AgroSci. Simazine Princep ® Syngenta Sulfometuron
methyl Oust XP ® DuPont Tebuthiuron Spike 20P ® Dow AgroSci. Triclopyr Garlon 3A, 4 ® Dow AgroSci.
Classification of Herbicides Application Method
Foliar Applied• Plant contact
Soil Applied• Soil contact
Broadcast• Entire area
Spot• Specified area
Classification of Herbicides Application Timing
Preemergence• Prior to seed
germination Postemergence
• After seed germination and active growth
Post-directed• Directed to
particular portion of plant once emerged and growing
Classification of Herbicides Plant/Soil
Environment Selectivity
• Selective vs nonselective
Systemic• Mobile vs non-
mobile in the plant Residual Activity
• Extended vs non-extended soil activity
Classification of Herbicides Formulation
Liquid• Solution• Emulsifiable conc.• Flowable
Dry• Soluble powder• Wettable powder• Dry flowable• Granular
Classification of Herbicides Mechanism of
Activity “Why You See
What You See When You See”
Focus of the discussion
Lets take some time discussing how herbicides kill their target and what it looks like.
What To Do If Herbicide Injury is Suspected. 1. Seek background information.
History of the area. 2. Evaluate what is seen.
Look at the roots. Loot at the stems. Look at the leaves.
Consider all possible options or situations.
What To Do If Herbicide Injury is Suspected. Identify possible source.
Off-target movement. Wrong herbicide. Improper Application. Other options/ideas???
Herbicide Behavior in Plants To understand
herbicide injury we need to understand the ways in which herbicides do their job.
Remember!!!!
“Herbicide injury, in most cases, is the
result of the herbicide, doing
what it was designed to do, in the wrong place at the wrong time.”
Active Ingredients Approved for Use on BLM
Atrazine AAtrex Nine-O ® Syngenta Bromacil Hyvar ® DuPont Chlorsulfuron Telar ® DuPont Clopyralid Transline ® Dow AgroSci. 2,4-D various several Dicamba Clarity ® BASF
Vanquish ® Syngenta Diuron Karmex ® Griffin Fosamine Ammonium
Krenite ® DuPont Glyphosate Roundup Pro ® Monsanto
AquaMaster ® Monsanto Hexazinone Velpar L ® DuPont
Active Ingredients Approved for Use on BLM
Imazapyr Arsenal ® BASF Imazapic Plateau ® BASF Mefluidide Embark ® PBI Gordon Metsulfuron
methyl Escort XP ® DuPont Picloram Tordon 22K ® Dow AgroSci. Simazine Princep ® Syngenta Sulfometuron
methyl Oust XP ® DuPont Tebuthiuron Spike 20P ® Dow AgroSci. Triclopyr Garlon 3A, 4 ® Dow AgroSci.
Types of Herbicide Injury 1. Plant Growth Regulation 2. Photosynthesis Inhibitors 3. Photosynthetic Pigment Inhibitors 4. Plant Growth Inhibitors 5. Amino Acid Synthesis Inhibition 6. Lipid Biosynthesis Inhibition 7. Cell Membrane Disruption 8. Unclassified Activity
Active Ingredients Approved for Use on BLM
Atrazine Photosynthetic Inhibitor Bromacil Photosynthetic Inhibitor Chlorsulfuron Amino Acid Biosynthesis Clopyralid Plant Growth Regulator 2,4-D Plant Growth Regulator Dicamba Plant Growth Regulator Diuron Photosynthetic Inhibitor Fosamine Ammonium
Plant Growth Regulator Glyphosate Amino Acid Biosynthesis Hexazinone Photosynthetic Inhibitor
Active Ingredients Approved for Use on BLM
Imazapyr Amino Acid Biosynthesis Imazapic Amino Acid Biosynthesis Mefluidide Plant Growth Regulator Metsulfuron
methyl Amino Acid Biosynthesis Picloram Plant Growth Regulator Simazine Photosynthetic Inhibitor Sulfometuron
methyl Amino Acid Biosynthesis Tebuthiuron Photosynthetic Inhibitor Triclopyr Plant Growth Regulator
Types of Herbicide Injury 1. Plant Growth Regulation 2. Photosynthesis Inhibitors 3. Photosynthetic Pigment Inhibitors 4. Plant Growth Inhibitors 5. Amino Acid Synthesis Inhibition 6. Lipid Biosynthesis Inhibition 7. Cell Membrane Disruption 8. Unclassified Activity
Mechanism of Action & Herbicides Used
Plant Growth Regulating Herbicides
Plant Growth Regulation Activity is similar to that of IAA. Addition of “synthetic IAA” results in an
imbalance of the growth regulating hormone.
Cells of the leaf vein rapidly divide while cells between the veins do not.
Cell division and respiration increase, while photosynthesis does not.
Plant Growth Regulation What are you going to see visually?
1. Strap-like leaves - parallel veins in the leaves.
2. Downward twisting and cupping of the leaves.
3. Excessive adventitious root formation will be stimulated
upon root contact.
Plant Growth Regulation
Leaf Vein Cell DivideLeaf Vein Cell Divide
Inter-venal Cells Do Not DivideInter-venal Cells Do Not Divide
Plant Growth Regulation Examples include:
2,4-D Dicamba Picloram Clopyralid Triclopyr
How does this type of injury occur?
Drift - both particle and vapor. Improper cleaning of equipment. Applying when air temperatures
exceed those listed on the label. Exceeding the labelled rate.
Mechanism of Action & Herbicides Used
Photosynthetic Inhibiting Herbicides
Photosynthesis Inhibitors The photosynthetic process is shut
down. Generally applied to the soil, moves
through the plant in the xylem system.
Foliage and stems are affected, yet the root system is not.
Photosynthesis Inhibitors Plants exposed to treated soil will
germinate and emerge, take up the herbicide and move it to the leaves where it will result in injury.
Photosynthesis Inhibitors What are you going to see visually?
1. Plants turn yellow and die as a result of chlorophyll breakdown.
2. As the injury proceeds, the plant will turn brown and die from the bottom of the plant to the top of the plant.
3. Leaves initially turn yellow between the veins, dying from the tip towards the
base, and from the outer edge to the center.
Photosynthesis Inhibitors Examples Include:
Atrazine Bromacil Diuron Hexazinone Simazine Tebuthiuron
How does this type of injury occur?
Movement of treated soil - these herbicides are residual.
Lack of incorporation into the soil. Applying in an area where the root
system of desirable plants can take up the herbicide.
NOT READING THE LABEL. Failing to understand the residual
capability of these herbicides.
Mechanism of Action & Herbicides Used
Amino Acid Synthesis Inhibiting Herbicides
Amino Acid Synthesis Inhibition Injury is associated with a particular
enzyme, which, in turn, is associated with a particular amino acid process.
Visual results are the result of secondary injury – the injury as the beginning of a chain of events that take place in the plant. This is why the visual symptoms take time to
develop – it is not an immediate process.
Amino Acid Synthesis Inhibition
Amino Acid Synthesis Inhibition May or may not have soil activity. Activity associated with a particular amino
acid synthesis sequence. Acetyl CoA Carboxylase (ACCase) - Select Acetolacte Synthase (ALS) - Arsenal, Escort EPSPase Inhibitor - Roundup
Interference is translated to protein synthesis and inhibition of growth which takes time - slow acting.
Amino Acid Synthesis Inhibition What are you going to see visually?
Initially there will be a general yellowing of the treated plants.
After 5 to 10 days, chlorosis results in necrosis.
Amino Acid Synthesis Inhibition Imidazolinones
Arsenal Plateau Sahara Top Site
Glyphosate Roundup
Sulfonylureas Escort Oust Telar
How does this type of injury occur?
Drift - application on a windy day. Movement of treated soil. Failure to apply the correct amount – the
use rates are small and an error in measuring can make a large difference.
Summary Ideas By taking time to
learn about the visual symptoms associated with the different classes of herbicides - you can more easily understand what you see, when you see it.
Summary Just Remember:
“Worrying has killed more people than work because more people worry than work.”
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