PESTS AND DISEASES OF CROPS
BIOLOGY SSS 2 THIRD TERM
WEEK ONE
PESTS AND DISEASES OF CROPS
PERFORMANCE OBJECTIVE
Students should be able to;
- Identify pest
- Classify pest
- Define pest
- State the parts of a plant or animal that pests attack
CONTENT
A pest can be classified as an organism capable of causing damage to the crop plant. Pest are animals, insects, germs or other organisms that interfere with plant growth. They may bite, destroy food crops or damage farmland produce.
Types of Crop Pest
There are six classes
– Insects
– birds
– rodents
– monkeys
– nematodes
– man
Classification of Insect Pests
Insect pests are classified into various groups based on their mode of feeding. These group of insect pests are biting and chewing, piercing and sucking, boring insects.
- Biting and Chewing Insects – They possess certain qualities like strong mandibles and maxillae which enable them to bite and chew plant parts. Examples are termites, grasshoppers, leaf worms, armyworms, mantids, locusts and beetles.
- Piercing and Chewing Insects – These insects possess strong mouthparts called proboscis which enable them t pierce through plants and such liquid materials from plant tissues. Examples are aphids, cotton stainers, mealy bugs, scale insects, capsids or mirids and whiteflies.
- Burrowing Insects – These insects including their larvae are capable of burrowing into plant parts and destroying the tissues of the plants or fruits or seeds. Examples are bean beetles, stem burrowers, maize weevils and rice weevils.
Based on Location, insects can also be divided into two depending on whether they attack crops on the field or the products in the store. Insects that attack crops on the field are called Field Pests e.g. grass hoppes, caterpillar, locusts while those that attack the products in the store are referred to as storage pests. e.g weevils, beetles, moth.
Non-insect pests – These are bigger animals which can either be mammals or birds. They include rodents, squirrels, rats, monkeys, bats, goats and birds. These pests attack mostly cereal crops, maize, millet, sorghum, wheat and other crops during storage.
How do insects, pests attack the plant and affect it
Insects, pests attack the plants in three ways:
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- They cut the root, stem, and leaf.
- They suck the cell-sap from various parts of the plant and.
- They bore into stem and fruits. This way they affect the health of the crop and reduce yields.
Injury by Chewing Insects
Insects take their food in a variety of ways. One method is by chewing off external plant parts. Such insects are called chewing insects. It is easy to see examples of this injury. Perhaps the best way to gain an idea of the prevalence of this type of insect damage is to try to find leaves of plants with no sign of insect chewing injury. Cabbageworms, armyworms, grasshoppers, the Colorado potato beetle and the fall webworm are common examples of insects that cause chewing injury.
Injury by Piercing-Sucking Insects
Another important method which insects use to feed on plants is piercing the epidermis (skin) and sucking sap from cells. In this case, only internal and liquid portions of the plant are swallowed, while the insect feeds externally on the plant. These insects have a slender and sharp-pointed part of the mouthpart which is thrust into the plant and through which sap is sucked. This results in a very different but severe injury. The hole made in this way is so small that it cannot be seen with the unaided eye, but the withdrawal of the sap results in either minute white, brown or red spotting on leaves, fruits and/or twigs; leaf curling; deformed fruit; or a general wilting, browning and dying of the entire plant. Aphids, scale insects, squash bugs, leafhoppers and plant bugs are examples of piercing-sucking insects.
Injury by Internal Feeders
Many insects feed within plant tissue during a part or all of their destructive stages. They gain entrance to plants either in the egg stage when the female thrust into the tissues with sharp ovipositors and deposit the eggs there, or by eating their way in after they hatch from the eggs. In either case, the hole by which they enter is almost always minute and often invisible. A large hole in a fruit, seed, nut, twig or trunk generally indicates where the insect has come out, and not the point where it entered.
The chief groups of internal feeders are indicated by their common group names: borers; worms or weevils in fruits, nuts or seeds; leaf miners; and gall insects. Each group, except the third, contains some of the foremost insect pests of the world. In nearly all of them, the insect lives inside the plant during only a part of its life and emerging sooner or later as an adult. Control measures for internal feeding insects are most effective if aimed at adults or the immature stages before their entrance into the plant.
Several internal feeders are small enough to find comfortable quarters and an abundance of food between the upper and lower epidermis of a leaf. These are known as leaf miners.
Gall insects sting plants and cause them to produce a structure of deformed tissue. The insect then finds shelter and abundant food inside this plant growth. Although the gall is entirely planting tissue, the insect controls and directs the form and shape it takes as it grows.
Injury by Subterranean Insects
Subterranean insects are those insects that attack plants below the surface of the soil. They include chewers, sapsuckers, root borers and gall insects. The attacks differ from the above-ground forms only in their position regarding the soil surface. Some subterranean insects spend their entire life cycle below ground. In other subterranean insects, there is at least one life stage that occurs above the soil surface; these include wireworm, root maggot, pillbug, strawberry root weevil, and corn rootworm. The larvae are root feeders while the adults live above ground.
Injury by Laying Eggs
Probably 95% or more of insect injury to plants is caused by feeding in the various ways just described. Also, insects may damage plants by laying eggs in critical plant tissues. As soon as the young hatch, they desert the plant causing no further injury.