December 2015. A farmer in India writes that he cultivates cotton, sugarcane, castor, papaya, chilli pepper, bananas and other crops. He would like to know why the cotton bolls are blackened as shown in the photo. Is it mirid damage? When the boll opens the lint is black. Please help to identify the problem.
There was no response from members; however, an investigation on the Internet [Editor] showed that Nigropora and Aspergillus are frequently found in cotton bolls, and that perhaps the bolls in the photo have been attacked by Nirospora oryzae or Aspergillus nigrum.
Boll rots are frequent in cotton – in California for instance the crop suffers yield losses of up to 4% due to fungi, and in some hot, humid seasons this increases to 15%. Of the several fungi found, Nigrospora oryzae, was common, with lower occurrence of Aspergillus flavus and A. niger. The fungi require a wound or natural opening to infect and rot the cotton bolls, but once inside pectinase enzymes are important in the establishment of the fungus and the development of disease.
A number of control practices have been suggested:
- Keep field free from weeds
- Avoid weak plant growth by controlling fertilization and irrigation
- Remove bottom leaves to aid air circulation
- Selection of varieties with small leaves and open growth habit
- Control of insects, especially the common boll worm.