Crop Plant Diseases

Crop Plant Diseases

Definition of Disease

A disease can be defined as any abnormal situation in an organism which affects growth and development. It can also be defined as the deviation from a normal physiological function of an organism.

A disease can be recognized by sign and these visible signs of diseases are called symptoms.

Organisms that cause diseases are called pathogens.


1. Blackpod disease of coco: It is caused b fungus called phytophthora palmivora.

Symptoms : Dark brown spot appear on cocoa pods which later turn black.

Mode of transmission:

  • By rain splash
  • Through air borne spores.

Prevention and Control :

  • Remove and burn or bury infected pod.
  • Spray the remaining pod with chemicals called fungicides.

2.  Maize Rust: It is caused by a fungus called puccinia polysora.

Mode of Transmission : It is transmitted by air-borne spores deposited on leaves.

Symptoms :Red or purple spots which appear on leaves. The leaves will eventually die.

Prevention and control methods:

  • Resistant varieties should be planted.
  • Crop rotation should be practiced.
  • Seed dressing/ treating of seed with chemicals e.g fungicides before planting.
  • Regular weeding should be carried out.

3. Maize Smut: It’s causative agent is a fungus called Utislago maydis.

Mode of Transmission : It is transmitted by wind.

Symptoms : The leaves, stems and cobs are covered with mass of black spores.

Prevention and Control.

  • Practice crop rotation.
  • Infected crops should be destroyed.

4. RICE BLAST: It’s causative agent is a fungus called piricularia oryzae.

Mode of Transmission :

  • It can be transmitted via infected seed.
  • It can also be transmitted through air-borne spores.

Symptoms :

  • Long red spots appear on leaves and later turn yellow. An occurrence known as chlorosis.
  • The plant stem collapses.
  • Photosynthetic ability of the crop is reduced.

Prevention and Control :

  • Plan resistant varieties.
  • Potassium should be applied.
  • Seed dressing / treatment should be carried out.

5. MOULD (DISEASE OF STORED PRODUCE) : It is caused by a fungus called aspergillus specie.

Mode of Transmission :

  • Through infected seeds/fruits.
  • Through high humidity.

Symptoms :

  • Farm produce become mouldy.
  • Pungent smell
  • Sour taste.

Prevention and Control :

  • Proper drying of seeds before storage should be ensured.
  • Maintain low humidity in store.
  • Spray with fungicide.


1. Cassava Mosaic Disease : Its causative agent is virus.

Mode of Transmission :  It is transmitted by an insect knows as the white fly. It possess a piercing and sucking mouth part.

Symptoms :

  • Mottling of leaves
  • Leaves appear twisted
  • Leaves show bright yellow patches.

Prevention and Control:

  • Spray the crop with insecticides to kill the white fly which is its vector.
  • Uses resistant varieties.
  • Practice crop rotation.

2. Groundnut Rossette Disease : It is also caused by a virus.

Mode of Transmission : It is transmitted by a piercing and sucking insect known as the aphid.

Symptoms :

  • Malformation of leaves
  • Stunted growth
  • Yellowing of leaves (chlorosis)
  • Formation of witches broom of leaves.

Prevention and Control :

  • Spray the vector with insecticides
  • Practice crop rotation
  • Practice early planting.

3. Maize Steak Disease

Mode of Transmission : It is transmitted by leaf hopper which is a piercing and sucking insect.

Symptoms :

  • Yellowing of leaves
  • Stunted growth

Prevention and Control

  • Uproot and burn the infected plants
  • Use resistant varieties.

4. Bunchy Top Disease Of Banana

Mode of Transmission : It is transmitted by a vector known as Aphid.

Symptoms :

  • Stunted growth
  • Leaf curl.

Prevention and Control:

  • Practice good sanitation
  • Uproot and burn affected plant.

5. Swollen Shoot Disease Of Cocoa.

Mode of transmission : It is transmitted by a mealy bug.

Symptoms :

  • Swelling of branches.
  • Malformation of leaves
  • Premature dropping of leaves

Prevention and Control :

  • Destroy and burn infected plants
  • Spray with insecticide to kill vector.
  • Plant resistant varieties.


1. Define the term disease.

2. What are the causative agents of the following dieseses?

  • Maize Smut
  • Rice blast
  • Blackpod disease

3. Write two symptoms of the following diseases

  • Mould
  • Cassava mosaic disease.
  • Groundnut rosette disease.