COTTON. 183 



(a) Koot-rot (Ozoniuin omnivorum). — The fungus attacks 

 the roots and causes the whole plant to wilt suddenly, then die. 



(b) Anthracnose {Colletotrichimn gossypii). — This fungus 

 is responsible for the greater part of the rotting of the bolls of 

 cotton. The use of diseased seed constitutes one of the methods 

 by which anthracnose is spread. The disease also affects the 

 leaves and stems ; it is worst during damp weather. Small 

 discoloured depressions appear on the boll, which become grey- 

 ish and eventually become covered with pinkish spores. Either 

 a single lock or the entire contents of the boll may be rotted, 

 or the disease may keep the boll from opening widely. Dry 

 weather checks the disease, which will then appear only as a 

 reddening or spotting of the surface of the boll without serious 

 damage to the crop. Duggar advises wide spacing, avoiding 

 the use of nitrogenous fertilisers, planting the less leafy varie- 

 ties and those which show a certain amount of resistance to 

 disease. 



(c) Cotton Eust or Black Bust (Macrosporiinn nigrican- 

 tium) causes the premature loss of foliage, and consequently 

 when bad a much depreciated yield. The leaves show at first 

 a mottled, yellowish colour. After wet weather there may be 

 no yellowing, but a sudden blackening, drying and falling off 

 of the foliage. 



(d) Angular Leaf Spot (Pseiidomonas malvacearum) : The 

 organism produces through stomatal infections, water-soaked 

 angular areas, which later turn purple and finally become dry 

 and brown. 



Besides these, Rhyzoctonia (Corticium vagum), Leaf Spot 

 (Cercospora Gossypina) and {Spcerella Gossypina) and Cotton 

 Wilt i'N eocosmospora vasinfecta) may cause a certain amount 

 of injury. 



REFERENCES : 



"Cotton."— C. W. Burkett. 



" Cotton." — Peake. 



" Botany of Crop Plants." — Robbins. 



" The Cotton Plant in Egypt."— Balls. 



" The Improvement of Cotton by Seed Selection."— J. du P. 



Oosthuizen, Union Dept. of Agric. Bulletin 17, 1921. 

 " Cotton and Cotton-Seed Products." — Taylor, Industries Bulletin 10. 

 " Cotton Marketing."— Hesse; Journal, Dept. of Agric, June, 1922. 

 " Productive Farm Crops."— Montgomery. 

 " Cotton Pests of South Africa." — Braine: Union Dept. of Agric 



Bulletin 59. 

 Bailey's Enclo. of American Agric. 



