Theory question 105
Crop DiseasesDescribe briefly the side effects, preventive and control measures of diseases and pests of crops, under the following headings:
(a) chemical control
(b) biological control
(c) cultural method of control.
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(a) Chemical control – use of pesticides (insecticides, fungicides, nematicides) by spraying, dusting, seed dressing, fumigation; side effects: pollution of air, water and soil, poisoning of man and animals, residues in food, killing useful organisms, pests developing resistance
(b) Biological control – using natural enemies (predators, parasites, pathogens) e.g. parasitic wasp against cassava mealybug; side effects: slow, enemy may become a pest itself or attack useful organisms
(c) Cultural control – crop rotation, early planting, clean seed, burning/removing infected plants, resistant varieties, correct spacing, weeding, fallowing; side effects: labour-intensive, slow, may need more land
For each method give how it is done and at least two side effects.