114 DISEASES OF TROPICAL PLANTS OH, 



This disease is well worthy of a thorough investiga- 

 tion. In the meantime it has been recommended that 

 in districts where this disease is prevalent, the planters 

 should avoid varieties which make excessive growths, 

 use well-drained land, leave abundant space for cultiva- 

 tion and free circulation of air, and use acid phosphate 

 only for fertilization. 



Another bacterial disease, caused by Bacillus mal- 

 vacearum, is said to be very destructive to the Egyptian 

 and Sea Island Cotton in Nyassaland. 



Shedding of Bolls. The cotton crop in the United 

 States frequently suffers from a premature shedding of 

 the bolls. This may be due to fungus and insect 

 injuries, but is more probably due to any one of a number 

 of non-organic causes, such as character of the soil, ferti- 

 lizers, rainfall, etc. It must be studied separately in 

 each cotton-growing country. 



Cotton Rust. This is a true rust caused by the 

 fungus Uredo gossypii? Lager. It occurs on all parts 

 of the green plant, spreading from the older parts to 

 the new leaves as rapidly as they are formed. On the 

 upper side of the leaf it produces small rounded, or 

 angular, purplish brown spots. The spores are borne 

 in pustules just beneath the epidermis, which finally 

 ruptures and sets them free. These pustules are far 

 more abundant on the under than on the upper surface 

 of the leaf. 



Kust was first reported from Ecquador, and is very 

 abundant in the United States and the West Indies. It 

 is much more severe on the strictly tropical varieties than 

 on those grown in the semi-tropical and temperate zones. 

 The varieties grown in the Southern United States are 

 partially immune, even when grown in the West Indies. 



The destruction of the rubbish from the fields, and 

 such cultivation and fertilization as will result in 

 vigorous plants, will do much to control the trouble. 

 It is also wise to avoid the badly affected plants when 

 selecting the seed. 



1 Syn. Uredo of Kuehneola gossypii, Arthur. 



