“herbicides and their mechanisms of action” integrated pest management & certification...

“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


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.”


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


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


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


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.


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


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.


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


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.”

“herbicides and their mechanisms of action” integrated pest management & certification...

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