COTTON DISEASES 417 



the rows; (2) avoiding the use of nitrogenous fertilizers, 

 which induce a rank growth of the plant ; and (3) planting 

 those varieties which have not an excess of foliage, and 

 which show partial resistance to this disease. Anthracnose 

 of the bolls is most troublesome on rich land or on that 

 which is highly fertilized, especially with nitrogenous fer- 

 tilizer. While the worst injury is done to the bolls, this 

 disease also attacks the young seedhngs, the stem or 

 branches of theJarger plants, and the leaves. 



Disinfection of the seed by dipping them in a 3 per cent 

 solution of ^ormahn has been recommended, but not 

 generally practiced. This would have the effect of destroy- 

 ing such germs as might have lodged on the outside of the 

 seed, and hence this treatment might reduce the amount 

 of injury. However, no treatment of the seed can destroy 

 all of the fungus, since this organism penetrates the parts 

 inside the seed-coat or hull. Apparently the use of dis- 

 eased seed constitutes one of the methods by which boll-rot 

 is propagated. Hence seed from diseased bolls and even 

 seed from badly infected fields should be avoided. 



387. Cotton-rust or black-rust. — Cotton-rust causes the 

 premature loss of the foliage. This reduces the weight 

 or prevents the maturing of late bolls. It is probably 

 the most widely prevalent destructive disease of cotton. 

 The yield may be reduced by a severe attack of rust as 

 much as 50 per cent. 



Several different kinds of fungi are found in the diseased 

 foUage, but these are thought to be unable to gain entrance 

 into the leaves until unfavorable conditions of weather 

 or soil have weakened the plant. Cotton-rust is usually 

 worse in hot weather following a period of heavy rains. 

 2e 



