A grasshopper. Image credit nutrainigridients.com

A grasshopper. Image credit nutrainigridients.com

ZIMSEC O Level Combined Science Notes: Plant pests and diseases

  • In the wild there is a balance in nature.
  • The are few pests and diseases that destroy plants.
  • In crop plants there are more pests that cause and spread disease.
  • This is because there will be more plants of the same type concentrated together.
  • As a result pests can feed, multiply and spread easily from one plant to another.
  • Agriculture is constantly under threat unless people are aware of pests, the diseases they cause and the measures of controlling them.
  • A pest is any organism, plant or animal which is harmful to people and their activities.
  • There are different types of pests.
  • Some cause damage to crops by eating them, others are very small and they are only seen by the damage they cause.
  • The damage caused by pests results in reduced plant productivity.
  • The yields of fruits and seeds may be reduced by pests.
  • Thus effective pest control is important.
Tissue eating pestsSap sucking pestsBacterial wilt diseaseFungal rust disease
Type: Cutworms, grubs, locusts and grasshoppers, larvae and caterpillars,beetles, crickets, slugs, snails, millipedes.Type: Red spider. Very small and often abundantType: the organisms are microscopic.Type: the disease is caused by microscopic fungi which live in the stems and leaves of plants
Symptoms: holes, gaps, cut edges to plant organs. The damage is caused by pests eating plant roots, stems and leaves. Slugs, snails and millipedes eat roots and young shoots.Symptoms: damage reflected by spots on leaves and stem, wilting and premature drop. Often young seedlings and lawns, ( tufts, brown patches, death)Symptoms: damage caused includes: browning of shots and a slimy oozing when the stem is cut. Plans affected include: tomato, potato, sunflower and tobacco.Symptoms: evidence is the appearance of different sized pustules on the surface ( orange or yellow). Crops affected many cereal crops like maize, sunflower and beans.
Control: Carbaryl/8 SS. Snail baitControl: Lime sulphur in water or Kelthane HF or Dimethoate 40 EC.Control:little, apart from improving drainage, using good seed and rotating cropsControl: Dithane M45 or using resistant variables. Isolation of infected plants and crop rotation

Credit: Focus on Science Book 3

To access more topics go to the Combined Science NotesĀ page.

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