Competition for food

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.

Control measures Selective breeding (developing strains resistant to disease Plant and pest control through pesticides and herbicides.

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

DDT Organochlorine insecticides

How does DDT compare? Ease of manufacture Specificity Persistence in soil Cost Marketability Leaching losses and their effect Toxicity to other livuing organisms patents Cheap to produce as it was a one stage process Helped to reduce malaria and typhus Very stable Cheap available to developing countries Low toxicity to humans

Developed resistance Enzymic removal of DDT (HCl) Persistence in the soil for many years DDT builds up in fatty tissues of animals in food chain

Pyrethrin sensitive to air and light Biocypermathrin More active need small amounts biopermethrin Modifications to lead compound

Pyrethoids Conc of 1X active

How do they work They penetrate the cell membranes (long chain hydrocarbon 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 polar hydrocarbon tails Ionisable groups

Partition coefficient is very high. Known as Log K OW (octanol/water) Partition coefficient K = [x]in solvent A [x] in solvent B Disrupts the passage of potassium and sodium ions causing disrutption in nerve transmission

Environmental aspects Hydrolysis of ester group occurs naturally Or General oxidation Products are polar and soluble in water