Thursday, March 28, 2024
General Agriculture

Definitions, Classification, and Description of Important Pests of Crops

It is estimated that world crop losses due to pests are of the order of about 35 per cent of potential yield, but in most tropical countries of Africa and Asia, the field and store losses are of a higher magnitude and may be as high as 50 per cent in some cases.

FAO estimates showed, for example, that nearly 100 million metric tons of cereals grains are destroyed by pests each year. Diseases are estimated to cause about 10 per cent loss of the annual agricultural production in the USA and about 20-30 per cent in the developing countries.

Therefore, it is now widely recognized that the reduction of losses due to pests and diseases is an important element in increasing the efficiency of crop production.

This article starts with explanation of what a pest is and the different categorization of pests based on economic threshold of their effects on crops, on feeding patterns, on crops and the basic principles of pest control.

The various methods of pest control are discussed with emphasis on prevention rather than the control of pest. Definition of diseases, description of disease causing organisms, symptoms of plant diseases and control and preventive measures are extensively discussed.

Definition and Classification of Pests of Crops

Pest is any animal or plant which harm or causes damage to man, his animals, crops, or possession.

On agricultural basis, a pest is that which causes a loss in yield or quality of the crops resulting in loss of profits by the farmer.

When a loss in yield reaches certain proportions, then, the pest can be defined as an economic pest. When a loss in yield in a particular crop reaches 5 to 10 per cent a pest status is established.

Economic damage is the amount of injury done to a crop which will justify the cost of artificial control measures. The economic injury level is the lowest pest population density that will cause economic damage to a crop and this varies from crop to crop, season to season, and area to area.

Economic threshold is defined as the population density at which control measures should be started to prevent an increasing pest population from reaching the economic injury level.

Classification of Pests On The Basis Of Economic Threshold

1. The Regular Pests

These are pests which perennially damage crops and whose population levels rarely fall below the economic threshold.

Examples of these are Marucatestulalis on cowpea, Dysdercus spp. and red boll-worm on cotton, sorghum midge and Quelea birds in most parts of the grain producing Guinea and Sudan savanna of tropical Africa.

2. The Occasional Pests

These are pests whose populations levels are normally below the economic threshold but occasionally rise above it.

Examples of these include locusts that periodically ravage cereal crops and grasses in Sub- Saharan Africa, the stem borers and armyworms of cereals in western and eastern Africa, the variegated grasshopper, Zonocerus variegates, in West Africa, and many species of snails and lepidopterous larvae attacking deciduous forest trees, and arable and plantation crops.

3. The Potential Pests

Those pest whose population levels are usually considered to be far below the economic threshold but which can become highly injurious under changed cultural conditions or as introduced pest.

Examples of these include many species of grasshoppers and caterpillars in western and central Africa.

Read Also : Pest Management and Symptoms of Diseases on Crops

Brief Description of the Important Pests of Crops

The arthropods which comprise the insects, mites, millipedes and woodlice constitute the most dominant group, other of organisms include: nematodes, rodents, birds and mollusks.

1. Insects

Insects belong to a group of organism known as arthropods. Their small size, remarkable range of adaptation, rapid rate of reproduction, great mobility and efficient water conservation enables them to colonize nearly every habitat, including all the types in which crop production takes place.

Pests

These features of insects contribute towards making their control of paramount importance to the farmer.

Some insects are beneficial as pollinators of flowers and as predators which feed on destructive insects.

Other types of insects are directly harmful as pest of crops, as carriers of diseases and as destroyers of stored food. Insects’ pests exhibit three basic feeding patterns, namely: Biting and chewing, sucking, and boring insects.

1a. Biting and chewing insects

These are insects which have biting mouth parts consisting of a pair of toothed horny jaws (mandibles) and a pair of accessory jaws. They tear and bite plant parts in their larval or adult stages.

As a result, most of the leaves on the plant are eaten up. The grasshopper or locus, chewing beetle, the larvae of many butterflies and moths, the caterpillars are all examples of chewing insects.

1b. Sucking insects

These differ from biting insects in that they have mouthparts which extract the sap from plants.

This consists mainly of a long, powerful, piercing proboscis with which these insects suck the liquid cell contents from leaves, stems or fruits.

Sucking has weakening effect on plants but the ability to transmit plant diseases such as viruses is the most serious effect which sucking insects have on crops.

The commonest types of sucking insects are those which have probosces both at the immature and mature stages of growth. These insects feed on the stems and young fruits of many crops and may also introduce poisonous toxins into the crop tissues.

Capsids are typical example of this group of insects that attacked both young and old shoots and pods of cocoa. The cotton stainer is a troublesome sucking insect pest of cotton. It feeds on the young pods, and reduces the commercial value of cotton by staining the lint.

Other types of sucking insects include; scale insects, mealy bugs and aphid. Scale insects have shell that protects them during adverse weather condition and from predators.

Read Also : How to Control Cassava Diseases and Pests

Scale insects are found mostly on tree crops such as oil palm, cocoa, citrus, etc. they feed on the leaves and stems of tree crops, weakening them and reducing their productivity and life span.

Mealy bugs feed on the leaves and stems of young cocoa and citrus trees. Aphids are serious agricultural pests, carrying virus diseases from plant to plant through their piecing mouthparts. They feed mainly on young stems. Aphids transmit swollen shoot disease of cocoa in Africa.

Fruit piecing moths are sucking insects which feed mainly on citrus fruits. Their probosces are very powerful and easily pierce the skin of the fruits and in some cases, the holes made by the insects allow the entry of organisms responsible for causing decay.

1c. Boring insects

These have mouth parts which are adapted to digging holes through plant and material. The cowpea weevil which infests cowpea is a good example of boring insect.

2. Nematodes

These are small organisms which are normally referred to as eelworms. Nematodes can cause a considerable damage to crops such as yams, cowpea and many vegetable.

A disease known as root-knot disease of cowpea, for example, causes the formation of irregular nodules on the roots and dwarfing of the mature plant.

3. Rodents

These are mammals with teeth which are well adapted to gnaw or grind hard substances. They include mice, squirrels, porcupines, rats and grass cutters.

These animals may damage fruits and vegetables and are particularly very injurious to young seedlings of oil palm, rice, sugar cane, and the tubers of root crops such as cassava.

The larger rodents such as squirrels and grass cutters can be trapped, and wire netting fences may be erected to protect crops from damage.

Small rodents can be prevented from destroying young seedling of palm trees by placing collars of small-mesh wire netting around the base of the trunk.

4. Birds

Birds of various types may do considerable damage to grain crop farms by eating both developing and dry grains. Queleabirds are by far the most populous and destructive birds in Africa.

They invade crops like locust and cause heavy damage. Attacking the birds at their nesting and resting sites provides the most effective method of control. Toxic chemicals sprayed at dusk, has been found to be cheap and effective.

5. Mollusks

Garden snails and slugs may damage leaves of many kinds of vegetable.

Read Also: Ewedu Leaves (Jute Leaves): Facts, Health Benefits and Uses

Agric4Profits

Benadine Nonye is an agricultural consultant and a writer with over 12 years of professional experience in the agriculture industry. - National Diploma in Agricultural Technology - Bachelor's Degree in Agricultural Science - Master's Degree in Science Education... Visit My Websites On: 1. Agric4Profits.com - Your Comprehensive Practical Agricultural Knowledge and Farmer’s Guide Website! 2. WealthinWastes.com - For Effective Environmental Management through Proper Waste Management and Recycling Practices! Join Me On: Twitter: @benadinenonye - Instagram: benadinenonye - LinkedIn: benadinenonye - YouTube: Agric4Profits TV and WealthInWastes TV - Pinterest: BenadineNonye4u - Facebook: BenadineNonye

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