6 



The importance of the disease, however, does not lie so much in the 

 amount of the present loss as in the danger of its future increase, for 

 it must ultimately spread so much as to entail far greater losses and 

 possibly threaten the life of the industry unless the methods for its 

 control are perfected. 



DESCRIPTION OF THE DISEASE. 



The wilt is very distinct from any other disease of cotton, so that 

 there need be no difficulty in its identification. It usually makes its 

 first appearance in the spring about the last of May, when the iDlants 

 are 6 to 8 inches high. It appears in well-defined areas, which enlarge 

 if cotton is planted on the same land again. The first outward indi- 

 cation of its presence is a dwarfed growth and unhealthj^ appearance 

 of the plants. The leaves turn yellow between the veins, their mar- 

 gins shrivel up, and some plants wilt and die at once. In other plants 

 the progress of the disease is often slow, and many of them live the 

 entire summer and die late in the season. On cutting across the stem 

 of a diseased plant, the woody part will be found to be stained brown 

 Avherever the disease is present. In the absence of microscoi^ic 

 examinations, this brown discoloration of the internal tissue is the best 

 ocular evidence of the presence of the wilt disease. 



Plants may partiall}^ recover from a severe attack of the wilt disease 

 b}' the development of strong lateral branches near tlie ground. Such 

 l^lants may be distinguished by their dwarfed and bushy aiJijearance 

 and by the tendency of their branches to lie prostrate on the ground. 



CAUSE OF THE DISEASE. 



The cause of the wilt disease of cotton is a fungus, Neocosmospora 

 vasinfecfa (Atk.) Erw. Sm., which attacks the plant from the soil. 

 It first enters the smaller roots and subsequently grows from these 

 into the taproot and stem, filling the water ducts with its mycelium. 

 The result is that the supply of food and moisture carried up from 

 the roots is greatlj^ decreased and the symptoms described above are 

 produced. The nature of the fungus has been full)' discussed in 

 Bulletin No. 17 of this Division,^ and it will not be necessary to enter 

 into details here, but only to outline the subject and to record some 

 additions to our knowledge. 



The wilt disease of okra is believed to be caused by the. same fungus 

 which produces the cotton wilt. No inoculation experiments have 

 been tried, but in the experience of the writer okra has never failed 

 to contract the disease when planted in fields infected with the cotton- 

 wilt disease. 



1 Smith, Erwiu F. Wilt Disease of Cotton, Watermelon, and Cowp6a. 1899. 



