Weed Biology and Herbicides

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Weed Biology and Herbicides

• Weeds
• Reasons for success
• Problems for agriculture
• Herbicides
• Demand
• R D Costs
• Modes of Action

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What are pests?
Major weed plant families
grass
potato
morning glory
spurge
bean
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Reasons for success

• High reproductive rates
• Seed reservoirs

Vs. crop
4
3. Mimicry in hand weeded rice fields
Barnyardgrass
Rice
5
Seed Mimicry mechanical harvesters
Lentil mimic
Normal vetch
Lentil
6
4. C4 Photosynthesis
C3 costs 18 ATP, but CO2 lost at high temps C4
costs 30 ATP, but CO2 loss at minimized in
bundle sheath cells
C4 Photo-synthetic Advantage
Light
Temperature
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8/10 Worst weeds use C4 photosynthesis
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Problems for agriculture
1. Yield Losses
9
2. Difficult crop handling
3. Decreased crop quality
4. Reservoirs of pests pathogens Or
5. Hybridization
Sorghum bicolor x Sorghum halpense good bad

Aggressive perennial Few seeds Fast vegetative
growth
Horizontal gene transfer ??