Diseases of the Sweet Potato 161 



black, sunken, circular spots on the surface. In the 

 early stages the spots appear as nearly round, but they 

 become larger and lose their shape somewhat. Fre- 

 quently nearly the whole of a potato is covered by this 

 disease. The tissues beneath the surface have a green- 

 ish tint, while the surface of the spot itself is often 

 metallic in luster. On the plants the disease begins as 

 small round spots and continues to grow until the whole 

 stem of the plant is rotted off. Frequently it extends 

 up the stem to the surface of the soil but never above. 



Black-rot was reported the first time in 1890 in New 

 Jersey, but it is probable that it occurred long before 

 that. Since then it has been found in practically every 

 part of the United States where sweet potatoes are 

 grown and also in the West Indies and New Zealand. 



The disease is known in New Jersey, Delaware, 

 Maryland, Virginia, Ohio, Illinois, Missouri, Iowa, Ok- 

 lahoma, Texas, Arkansas, North Carolina, South Car- 

 olina, Georgia, and Alabama, and it is possible that 

 it occurs wherever sweet potatoes are grown. Black- 

 rot has been found on the following varieties: Nancy 

 Hall, Yellow Jersey, Big-Stem Jersey, Red Bermuda, 

 Miles Yam, White Yam, Southern Queen, Pierson, 

 Early Red Carolina, Florida, Yellow Strasburg, Key 

 West Yam, Red Jersey, Dahomey, Red Brazilian, Yel- 

 low Yam, Vineless Yam, and Georgia. 



In all the regions mentioned, the disease is preva- 

 lent on the plants or slips in the hotbed and on the 

 potatoes in the storage-houses in the winter; in fact, 

 heavy losses are caused by this disease in storage-houses, 

 where it develops freely under favorable conditions and 

 renders the potatoes unfit for consumption. 



The same control methods in general should be ap- 



