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Competition for food

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Increasing yield

Improve on nutrient levels

Crop protection before during and after Up to half of many crops are lost due to

disease pests and weeds.

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Control measures Selective breeding (developing strains

resistant to disease

Plant and pest control through pesticides

and herbicides.

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pesticides

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pesticides

What makes a good pesticide

Ease of manufacture

Specificity

Persistence in soil

Cost

Marketability

Leaching losses and their effect

Toxicity to other livuing organisms

patents

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DDT

Organochlorine

insecticides

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Developed resistanceEnzymic removal ofDDT (HCl)

Persistence in the soil for many years

DDT builds up in fatty tissues of animals in

food chain

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Pyrethrin sensitive

to air and light

Biocypermathrin

More active need

small amounts

biopermethrin

Modifications to lead

compound

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Pyrethoids

Conc of 1X 10-12 active

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How do they workThey penetrate the cell membranes (long chainhydrocarbon with a polar head) They are very soluble in

oils c.f. water and are easily taken up from aqueous

sprays through the insects .

Non polarhydrocarbon

tails

Ionisable groups

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Partition coefficient is very high.

Known as Log KOW (octanol/water)

Partition coefficient K = [x]in solvent A

[x] in solvent B

Disrupts the passage of potassium and

sodium ions causing disrutption in nervetransmission

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Environmental aspectsHydrolysis of ester group occurs

naturally

Or General oxidation

Products are polar and soluble in

water