Herbicide Demand

1
Herbicide Demand
When why?
2
Herbicide R D Costs
13 yr to breakeven
7 yr
3
Herbicide R D Costs
140 mil US
4
Herbicide Modes of Action

• Contact vs systemic
• Acute toxicity

5
Herbicide Modes of Action

• Inorganic (contact)
• Ex. Cu2SO4, NH4SO4
• Plasmolysis

• 2. Auxin-like (systemic)
• Phenoxy-acids 2,4-D 2,4,5-T
• Rapid stem elongation
• Cells starve

2,4,5-T agent orange - contam. W/ dioxin
6
3. Photosynthesis Inhibitors
Most target light rxn
7
Light-dependent Rxn
Diquat, paraquat
Atrazine
Atrazine inhibits photolysis of water
8
(No Transcript)
9

• Ex. Triazines
• Contact
• Pre-emergent
• Corn, soybeans, wheat, blueberries

Aq. Spp richness

• Acute Toxicity
• Mammals 1500-3000 ppm
• Fish 10-15 ppm
• Daphnia 7 ppm

Rel. Abundance

• Sub-lethal Toxicity
• Aq. Insect comm. Structure 20 ppb
• Algal growth 1 ppb

10

• Atrazine
• Fate in environment
• Moderate persistence
• 7-9 mo. Half-life
• dry-year carryover
• Surface water
• 1-70 ppb rural creeks
• 1000 ppb agric. ditches etc.

11

• 4. Metabolic Inhibitors
• Dintrophenols x electron transport
• Round-Up- Amino Acid Synthesis Inhibitor

AA synthesis in plants vs animals 9 essential
amino acids dietary only for animals Histidine
Isoleucine Leucine Lysine Methionine Threonine
Tryptophan Phenylalanine Valine
12

• Round-Up (A.I. glyphosate)
• Non-selective
• Post-emergent
• Low residual activity
• Water soluble- great systemic
• Good for rhizomes

Phosphophono- amino acid
13
Glyphosate kills EPSP enzyme so no aromatic
a.a.
Aromatic a.a.
EPSP enzyme
Not toxic to animals?
14

• Glyphosate Toxicity to Plants
• Primary
• Slow, 3 weeks
• Depletes aromatic a.a.
• no protein synthesis
• NH3 accumulates (toxic)
• Secondary
• Aromatic a.a. sustain auxin
• So- glyphosate speeds auxin breakdown
• More lateral growth
• Shallow root tillering

15

• Herbicide Resistant Crops
• How?
• Insert constitutive EPSP gene
• Examples
• Round-up Ready Corn Soybeans
• Pros Cons
• Others insect resistant crops (StarLink corn- Bt
  genes)