106 DISEASES OF TROPICAL PLANTS 



CH. 



is controlled in one locality at least by the application 

 by kainit, 400 Ibs. to the acre. 



COTTON 



Cotton is one of the most important tropical and 

 semi-tropical crops. It is subject to a great number of 

 diseases, many of which are no doubt as widely distri- 

 buted as the plant itself. Some of the diseases mentioned 

 here have not been reported from tropical countries, 

 but no doubt many of them are in the tropics and will 

 be reported at some future time, while others may be 

 introduced at any time. It is therefore very important 

 that they should be considered in a work of this kind. 



Damping Off ; Sore Shin ; Seedling Rot. The seedlings 

 of cotton, and also of many other plants, frequently 

 suffer from a disease which causes the stem to wilt, fall 

 over, and die. In short, the diseased plants behave in 

 the same manner as tobacco, vegetables, and many other 

 plants when grown in seed-beds. 



The young cotton plants, when attacked with this 

 disease, rot at or near the surface of the ground. 

 Sometimes this is a soft rot which works very rapidly 

 and results in the early death of the plants. This is 

 the well known " damping off or seedling rot." In 

 other cases it starts as an ulcer or sore on one side of 

 the plant, just below the surface of the ground, works 

 slowly, and shows a reddish brown colour. The ulcer 

 gradually deepens, sometimes extending into the 

 vascular system. This is known as sore shin, and is 

 not necessarily fatal to the plants. If the ulcer is 

 superficial the plant usually recovers and many of 

 them live, even when the ulcer has penetrated the 

 vascular tissues. Pythium Debaryanum, Hesse, 

 Glomerella gossypii, (South worth) Edg., and Rhiz- 

 octonia sp., are responsible for most of the "damping 

 off" troubles and seedling diseases in general, but it has 

 not been demonstrated that they are the cause of these 

 diseases of the cotton. 



