“Herbicides” Mode of Action Reeves Petroff Pesticide Education Specialist et al. MSU Extension

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

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 Mode of action (MOA) How it kills

Focus of the discussion How certain herbicides kill their target What damage looks like!

Herbicide Modes of Action 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

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 Mimics natural plant hormone – Auxins. Results in an imbalance of this 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.

Common Leaf Symptoms from PGR Exposure normal cupped and blistered from PGR exposure

short internode accumulation In new growth Foliar PGR Application

callus formation on roots translocation to growing point swollen hypocotyl lack of root development Root Absorption of Plant Growth Regulator Herbicides

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 labeled 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 Amino Acids = life!! Specific to plant AAs only Visual results are the result of secondary injury the injury as the beginning of a chain of events that take place in the plant. 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.

Plateau or Escort Injury Symptoms Stunting Chlorosis of youngest tissue

Glyphosate (Roundup) Drift chlorosis shortened internodes stem proliferation

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 Know symptoms associated with the different classes of herbicides Can more easily understand what to expect?.

Summary Just Remember: “Worrying has killed more people than work because more people worry than work.”