STUDY THE PESTS, DISEASES and WEEDS
Regular monitoring of pests, diseases and weeds is the basis for effective management. To be able to manage pests, diseases and weeds, information is needed
on the specific pests, diseases and weeds present in the region, village or crop fields and the associated damage they cause.
👉 Typical signs of pest attacks on crop plants
Most crop pests belong to the insects, mites and nematodes. Pest damage is obvious and easy to identify.
👉 Insect damage can be categorized by biting and chewing (e.g. caterpillars,
weevils), piercing and sucking (e.g. aphids, psyllids) and boring (e.g. borer, leaf
miner) species. Some are slow moving (e.g. caterpillars), fast moving (e.g. fruit
flies), hidden (e.g. stem borer), or easy to observe (e.g. caterpillars, weevils).
👉Pest damage is often species-specific: leaves with holes or missing parts is an indication of caterpillar or weevil damage; curled leaves is an indication of aphids; damaged or rotten fruits are often caused by larvae of fruit flies; withering plants can also be caused by larvae of noctuids or the stem borer; and branches or trunks with holes may be an attack by lignivorous insects.
👉Mites are very small and cannot be seen with the naked eye. However, some mite species (spider mites) weave a typical tissue on attacked plant parts and can, therefore, easily be detected. If mites are present on plants, leaves and fruits become yellowish.
👉Nematodes are also very small and therefore, they are not easy to observe
with the naked eye. They mostly attack plant roots; plants become yellow, wither and die.
Typical signs of disease attacks on crop plants
Most crop diseases are caused by fungi, bacteria or viruses.
👉Fungi cause the great majority, estimated at two-thirds, of infectious plant diseases. They include all white and true rusts, smuts, needle casts, leaf curls, mildew, sooty moulds and anthracnose. In addition, they are responsible for most leaf, fruit, and flower spots, cankers, blights, wilts, scabs, and root, stem, fruit, wood rots among many others. Parts of plants or the total crop plant can
wither and die.
👉Bacteria cause any of the four following main problems. Some bacteria produce enzymes that breakdown the cell walls of plants anywhere in the plant. This causes parts of the plant to start rotting (known as ‘rot’). Some bacteria produce toxins that are generally damaging to plant tissues, usually causing early death of the plant. Others produce large amounts of very sticky sugars; as they travel through the plant, they block the narrow channels preventing water getting from the plant roots up to the shoots and leaves, again causing rapid death of the plant. Finally, other bacteria produce proteins that mimic plant hormones. These lead to overgrowth of plant tissue and form tumours.
👉Viruses mostly cause systemic diseases. Generally, leaves show chlorosis or change in colour of leaves and other green parts. Light green or yellow patches of various shades, shapes and sizes appear in affected leaves. These patches may form characteristic mosaic patterns, resulting in general reduction in growth and vigour of the plant
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