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Pests and Diseases of Agricultural Importance

A pest may be defined as an organism (plant or animal) that depends on or competes with the crop for factors of life, like water, nutrients, sunlight, etc. The word pest comes from the Latin word pestis, meaning plague.

Bunting defined pests as follows: “In farming systems, many sorts of organisms compete with man at both the primary and secondary stages of production. They include insects, termites and other arachnids, ticks and other exoparasites of animals; nematodes and all other forms of harmful parasitic worms of both plants and animals; fungi, bacteria and viruses, higher plants (weeds and poisonous plants); birds and mammals. From man’s point of view, these are the vectors that transmit diseases. Some of them are harmful organisms and we refer to them collectively as pests. Examples of animal pests are insects (locusts, grasshoppers, beetles and weevils) and examples of plant pests are weeds, herbs, and shrubs.

Crops and farm animals suffer untold damage from pests and the diseases they cause. It is not possible to eliminate all pests in order to maximise agricultural production. In crop protection, the farmer should think of pest management or control, rather than pest eradication, which will cost more and take time to achieve.

1. Some crops and their pests: Pests may be classified by type of crop or farm animals or fish as shown in the table below:

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2. Control of pests

a.  Weeds: Weeds are controlled by the use of herbicides.

b. Insects: Insecticides are the main chemicals used in agriculture to control insect pests. They range from contact insecticides (which kill insects by mere contact with the insect), systematic insecticides kill insects when insects ingest them as they eat the tissues of stems of, say, maize. The insecticide goes into the stem of crop inner tissues and waits for the voracious feeding larvae or moths and butterflies (stem-borers).

c.  Nematodes; Soil nematodes are controlled by the application of nematicides, e.g,  furadan 3G or MOCAP 10G. In animals, e.g. pigs, sheep and cattle, roundworms (e.g, Ascaris iumbricoides) attack virtually all the organs and tissues of the body causing wasting, stunting and death of livestock. They are controlled by deworming the farm animals using appropriate worm expellers.

d. Birds: Birds in rice and maize fields are controlled manually by clapping with hollow wood or using caricature scarecrows. They are also controlled by chemicals that cause them to panic, put them in alarm situation and they cannot settle.

e. Mammals: The main pests in this category are rodents. They are controlled by traps or the use of rat poison like raticides.

Some crop diseases and their control: The below table summarises the diseases of some crops and their control measures:

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Pests of agricultural importance: These are grasshoppers, weevils (bean, flour, maize, etc), grain moths, beetle, nematodes, etc.