34 COTTON 



increase in size, they turn black in the middle whilst 

 the edges remain of a pinkish hue. The pink colour 

 is due to a pigment contained in the spores of the 

 fungus. When the bolls are attacked before they 

 have attained their full size, they frequently become 

 deformed owing to unequal growth. In some cases, 

 the fungus penetrates the seeds, and thus ruins both 

 the seed itself and the cotton attached to it. The 

 disease occurs chiefly in warm, damp weather, during 

 the time that the bolls are developing and ripening. 



When the fungus attacks the stem, reddish-brown 

 patches appear on the bark, and as a result of the 

 injury produced the leaves may turn yellow, wither, 

 and fall to the ground. The damage is sometimes 

 serious when the stems of seedlings are attacked, but 

 the effect of the fungus on the stems of well-developed 

 plants is not as a rule very harmful. 



No direct remedy has yet been discovered for this 

 malady. The fungus is least prevalent in fields in 

 which the cotton is widely planted and thus enabled 

 to get plenty of light and air. The application of 

 artificial manures containing phosphates and potash 

 renders the plants more hardy and better able to resist 

 the disease. It is desirable in plantations in which 

 the blight has occurred that, after the cotton has been 

 picked, all the cotton-stalks and other remains of the 

 plants should be collected and burned. Cotton 

 should not be grown in such a field during the following 

 year. 



Wilt or frenching is caused by Neocosmospora 

 vasinfecta, a fungus which enters the plant through 

 the roots and gradually grows upwards into the stem 

 and branches. The circulation of the sap is thus 

 interfered with, and the plant is unable to obtain the 

 necessary nutriment. The lower leaves are the first 

 to show signs of the disease. They develop a yellow 

 colour on the under-surface, and gradually die, and 

 fall from the plant. In extreme cases, all the leaves 

 fall off and the plant dies. The disease can be 

 recognised by breaking the stem of the plant, when 

 the fibro-vascular tissues are seen to be of a light 

 brown colour. 



