“Herbicides”

Mode of Action

Reeves PetroffPesticide Education Specialist et al.

MSU Extension

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 Mechanism of

Activity Mode of action (MOA)

How it kills

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

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

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 ofyoungest tissue

Glyphosate (Roundup) Drift

chlorosisshortened internodes

stem proliferation

Amino Acid Synthesis Inhibition Imidazolinones

Arsenal Plateau Sahara Top Site

Glyphosate Roundup

Sulfonylureas Escort Oust Telar

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.”