Anthracnose (Glomerella gossypii)
It is caused by the fungus Glomerella (Colletotrichum gossypii). It is the primary cause of seedling blight, boll rot and fibre deterioration (staining) in all humid cotton growing areas. Seedlings affected by blight are killed before or after they emerge (damping-off).
Symptoms of seedling blight on cotyledons are usually diseased areas on margins or small reddish or light coloured spots. Diseased seedlings show reddish-brown lesions below ground. The lesions may be on one side of the stem or they may surround it and extend down the root. On the bolls the disease appears as small, round, water-soaked spots, which enlarge, become sunken and brownish in colour. In wet weather, the spots are covered with a sticky mass of fungal spores pinkish in colour.
Boll infection is often associated with wounds made by boll weevils. The lint and seeds are rapidly invaded once the disease gets through the husk of the boll. Affected lint is stained.
The disease survives on old rotten bolls, crop refuse in the field and on the seeds. It is spread on diseased seeds. Infection is favoured by moderate temperatures and high moisture.
- Use disease-free seeds.
- Practise crop rotation.
- Practise good field hygiene.