112 DISEASES OF TROPICAL PLANTS CH . 



mature not to rot, it is usually difficult to pick. The 

 disease is quite common in both the United States and 

 the West Indies, the annual loss ranging from 10 per 

 cent to 50 per cent. 



Leaf Blight. This disease is due to the Cercospora 

 stage of the fungus Mycosphaerella gossypina, Atk, 1 

 which occurs on the leaves of the plant causing the 



characteristic Cerco- 

 spora leaf-spot (Fig. 

 50). The spots are 

 small, whitish, of dead 

 tissue, and are sur- 

 rounded by a rather 

 indefinite reddish bor- 

 der. During the fall 

 and winter the Sphae- 

 rella or perfect stage 

 can be found in very 

 great abundance. The 

 disease may attack 

 plants at any stage of 

 their development, but 

 when unaccompanied 

 by other troubles it 

 causes very little 



FIG. 50. Cotton leaves affected with leaf blight, damage. It is widely 

 (After Cook and Home, Prime Informe Anual % -\ ,-\ -\ , 



de la Estacion Central Agronomica de Cuba.} distributed tnrOUgllOUt 



the United States and 



the West Indies, and no doubt occurs in other places 

 from which it has not been reported. 



Mildew. This disease is caused by the fungus 

 known as Ramularia areola, Atk. It does not appear 

 until the fall, when it may be found in the angles 

 formed by the veinlets. It causes well defined, 

 irregular, small, translucent, or light green-coloured or 

 yellow-tinted areas, which are most conspicuous on the 



1 The organism was first described under the name Cercospora gossypina, 

 Cke., but later studies proved it to be the Cercospora stage of Mycosphaerella 

 gossypina. 



