Lecture 19 Herbicide Modes of Action

7 Major Types of Herbicide MoA

1. Auxin-type Growth Regulators

2. Amino Acid Synthesis Inhibitors

3. Lipid Biosynthesis (ACCase) Inhibitors

4. Pigment Inhibitors

5. Photosynthesis Inhibitors

6. PPO Inhibitor/Cell Membrane Disruptors

7. Seedling Shoot/Root Inhibitors

Describe Auxin-type Growth Regulators

inhibits plant growth and development (cell elongation, root development)

Describe Pigment Inhibitors

prevents production of new carotenoids

Describe Lipid Biosynthesis Inhibitors/ACCase Inhibitors

halt meristematic activity by inhibiting the acetyl-CoA carboxylase (ACCase) enzyme that is involved in lipid synthesis

Describe Amino Acid Inhibitors

disrupts amino acid formation

Glyphosate is what kind of inhibitor?

Aromatic Amino Acid Inhibitor

Describe Branched Chain Amino Acid Inhibitors (ALS Inhibitors)

slowly starves plants of valine, leucine, and isoleucine (AA), leading to inhibition of protein biosynthesis

Describe Photosynthesis Inhibitors

leads to slow starvation; rapid death from production of secondary toxic products

Two Broad “Modes of Action”

1. Classical Photosynthetic Inhibitors

2. Rapid Acting Photosynthetic Inhibitors

Describe Cell Membrane Disruptors

rapid destruction of cell membranes and leakage of cell contents — generally contact and rapidly kill

Describe Microtubule/Spindle (Mitosis) Inhibitor

affect root growth by affecting mitosis and inhibits cell division

Auxin-type Growth Regulators are effective against which plants?

Broadleaf Weeds

Branched Chain AA Inhibitors affect which plants?

Grasses and Dicots

Aromatic AA Inhibitors affect which plants?

Grasses and Dicots

Microtubule/Spindle (Mitosis) Inhibitors affect which plants?

Grasses and Broadleaf Weeds

Auxin-type Growth Regulators — Symptoms

1. Leaf cupping

2. Strapping

3. Epinasty

4. Short, thickened roots

Pigment Inhibitors — Symptoms

1. Albication/Bleaching

2. Malformation

Lipid Biosynthesis Inhibitors — Symptoms

DLWC

1. Discoloration & Disintegration of Meristematic Tissue

2. Leaves turn yellow or red

3. Wilting

4. Chlorotic Banding

ALS Inhibitors — Symptoms

MYRP

1. Meristematic areas yellow and die

2. Yellow streaks on leaves

3. Red/Purple veins

4. Pruned Roots

Aromatic Amino Acid Inhibitors — Symptoms

YM

1. Yellowing and Wilting of shoots

2. Malformation

Photosynthesis Inhibitors — Symptoms

ICBS

1. Interveinal/Veinal Yellowing

2. Chlorotic/Necrotic Leaf Margins

3. Burning of Plant Tissue (postemergent app)

4. Spotted Leaf Yellowing or Bronzing (tolerant crops)

Cell Membrane Disruptors — Symptoms

RSL

1. Rapid Necrosis and Speckling of Leaf Tissue

2. Leaf Bronzing

Microtubule/Spindle (Mitosis) Inhibitors — Symptoms

SCL

1. Swelling of Root Tips

2. Clubbed Root

3. Lodging