Cotton
Anthracnose of Cotton
Glomerella gossypii
Fungus
In a Nutshell
- Reddish to light brown spots with black dying margins on leaves.
- Lesions on stems may cause plant death.
- Water-soaked spots on bolls, later enlarge into sunken, yellow lesions.
Can also be found in
Cotton
Symptoms
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.
Recommendations
Organic Control
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.
Chemical Control
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).
What caused it?
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.
Preventive Measures
- Please be aware of possible quarantine regulations in your country.
- Use only healthy and pathogen free seeds or transplants.
- Check if there are varieties resistant to this disease in your area.
- Sow seeds that have been previously delinted.
- Ensure that the field have a good drainage system.
- Add compost to enrich the soil and make plants more resistant to diseases.
- Avoid water logging and excess irrigation.
- Avoid sprinkler or overhead irrigation systems.
- Do not work in fields when plants are wet.
- Rogue weeds and possible alternative hosts.
- Keep ripening fruits from touching the soil.
- Remove infected plant debris from the soil surface after harvest.
- Plan a crop rotation of 2-3 years with non-susceptible crops.
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