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.

        FUNGAL DISEASES OF CROP PLANTS.

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.

               VIRAL DISEASES OF CROP PLANTS

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.

Questions

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.