Anthracnose in cotton can occur in all growth stages of the plant and it can affect all tissues. If the pathogen infects the seedlings, it produces small reddish to light brown circular spots with black necrotic margins on the cotyledons and primary leaves. If the lesions develop on the collar region, the stem may be girdled, causing seedling or young plants to wilt and die. In mature plants, the infection and colonization of the stem may result in the splitting and shredding of bark. Affected bolls have small, circular, water-soaked spots which can rapidly enlarge into sunken, yellow to brown lesions in humid conditions. The lint becomes a disorganized and brittle mass of fiber, turning yellow to brown. It is also common that the infected bolls cease to grow, dry up and burst prematurely.
The symptoms are caused by the fungus Collectotricum gossypium, also known as Glomerella gossypii. It can survive from one season to another as dormant on or in infected seeds in the soil and resume growth once the weather conditions are favorable. It can be spread through infected plant debris, rotten bolls or contaminated seeds over long distances. Within the field, the secondary infection takes place via spores dispersed by wind, rain, rain-splashes and insects. The pathogen also seems to survive in the weed hosts Aristolochia bracteata and Hibiscus diversifolius. Its growth is favored by warm and humid weather (29 to 33°C), prolonged rainfall at the time of boll formation or close planting.
To this day we are not aware of any biological control method available against this disease. If you know of any successful method to reduce the incidence or the gravity of the symptoms, please contact us.
Always consider an integrated approach with preventive measures together with biological treatments, if available. The treatment of seeds with fungicides like captan, carboxin or thiram at (usually 2g/kg of seeds) helps to reduce the incidence of the disease. Foliar sprays of the crop at boll formation stage with mancozeb, copper oxychloride will also reduce the gravity of the symptoms (2.5 ml/l of water).