“Herbicides and Their Mechanisms of Action” Integrated Pest Management & Certification Training Richard D. Lee IPM Specialist USDI-BLM

Journey in Time 1984: CyanamidBASF MilesEli Lilly DowDuPont StaufferShell ICI AmericasCIBA-Geigy MonsantoNor-AM Union CarbideHoechst Rohm & HaasVelsicol ZoeconISK Biotech FMCOrtho 20 companies

Journey in Time Early 2002: Syngenta Bayer BASF Dow AgroSciences DuPont Valent Monsanto FMC 8 companies

Active Ingredients Approved for Use on BLM AtrazineAAtrex Nine-O ® Syngenta BromacilHyvar ® DuPont ChlorsulfuronTelar ® DuPont ClopyralidTransline ® Dow AgroSci. 2,4-Dvariousseveral DicambaClarity ® BASF Vanquish ® Syngenta DiuronKarmex ® Griffin Fosamine AmmoniumKrenite ® DuPont GlyphosateRoundup Pro ® Monsanto AquaMaster ® Monsanto HexazinoneVelpar L ® DuPont

Active Ingredients Approved for Use on BLM ImazapyrArsenal ® BASF ImazapicPlateau ® BASF MefluidideEmbark ® PBI Gordon Metsulfuron methylEscort XP ® DuPont PicloramTordon 22K ® Dow AgroSci. SimazinePrincep ® Syngenta Sulfometuron methylOust XP ® DuPont TebuthiuronSpike 20P ® Dow AgroSci. TriclopyrGarlon 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 AtrazineAAtrex Nine-O ® Syngenta BromacilHyvar ® DuPont ChlorsulfuronTelar ® DuPont ClopyralidTransline ® Dow AgroSci. 2,4-Dvariousseveral DicambaClarity ® BASF Vanquish ® Syngenta DiuronKarmex ® Griffin Fosamine AmmoniumKrenite ® DuPont GlyphosateRoundup Pro ® Monsanto AquaMaster ® Monsanto HexazinoneVelpar L ® DuPont

Active Ingredients Approved for Use on BLM ImazapyrArsenal ® BASF ImazapicPlateau ® BASF MefluidideEmbark ® PBI Gordon Metsulfuron methylEscort XP ® DuPont PicloramTordon 22K ® Dow AgroSci. SimazinePrincep ® Syngenta Sulfometuron methylOust XP ® DuPont TebuthiuronSpike 20P ® Dow AgroSci. TriclopyrGarlon 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 AtrazinePhotosynthetic Inhibitor BromacilPhotosynthetic Inhibitor ChlorsulfuronAmino Acid Biosynthesis ClopyralidPlant Growth Regulator 2,4-DPlant Growth Regulator DicambaPlant Growth Regulator DiuronPhotosynthetic Inhibitor Fosamine AmmoniumPlant Growth Regulator GlyphosateAmino Acid Biosynthesis HexazinonePhotosynthetic Inhibitor

Active Ingredients Approved for Use on BLM ImazapyrAmino Acid Biosynthesis ImazapicAmino Acid Biosynthesis MefluididePlant Growth Regulator Metsulfuron methylAmino Acid Biosynthesis PicloramPlant Growth Regulator SimazinePhotosynthetic Inhibitor Sulfometuron methylAmino Acid Biosynthesis TebuthiuronPhotosynthetic Inhibitor TriclopyrPlant 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 Divide Inter-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

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.”