286 



worth is sometimes found, and Cercospora gossypina Cooke, 

 as well as its perfect stage, Sphmrella gossypina Atkinson is a 

 very common accompaniment of the trouble. The accompan- 

 iment of the Cercospora stage of Sphoerella gossypina fre- 

 quently produces a separate type of the disease, especially 

 when this fungus is more abundant than either the Macros- 

 porium or Alternaria. This usually occurs when the disease 

 progresses quite rapidly through the earlier stages, so that 

 the yellow color is soon diffused somewhat evenly over the 

 entire leaf or a large part of it." 



During the summer of 1896 the rust appeared to a limited 

 extent in the cotton plots grown on the Station farm. The 

 exp3riments in progress included fertilizer tests (see Bulletin 

 76, p.p. 20-23), in some of which considerable quantities of 

 kainit were used, but under the prevailing soil and weather 

 conditions it seemed to have no appreciable effect in controll- 

 ing the disease, the rusted areas crossing the kainit plots ir- 

 regularly. This unexpected result served to call attention to 

 the fact that neither the supply of potash in the soil nor the 

 effect of the kainit on its mechanical condition were the only 

 factors to be considered in studying the rust problem. 



The season of 1897 proved to be a very bad one for cot- 

 ton rust. In the poorer sandy fields south of Auburn the 

 stalks were nearly all bare of leaves by the first of Septem- 

 ber. In riding about the country it was everywhere noticed 

 that on the old fence rows that had been cleared up and put 

 in cultivation since the passage of a stock law a few years 

 ago, the cotton was still green ; and it remained green and 

 vigorous throughout the season in striking contrast to the 

 bare rusted stalks in the remainder of the fields. 



Here then seemed to be a key to the trouble. These old 

 sandy fields had been cultivated in cotton season after season 

 for many years, until their original fertility had been entirely 

 exhausted. The supply of vegetable matter or humus in par- 

 ticular was very scanty. The small amount of commercial fer- 

 tilizer put down with the seed in the spring, usually about 100 

 pounds per acre, served to give the young plants a start, but by 

 midsummer it was exhausted, leaving the plant with nothing 

 to support it during the trying process of flowering and fruit- 



