248 THE POTATO 



characteristic. Any one of the diseases of the 

 sweet potato may be present without causing se- 

 vere loss provided conditions are unfavorable to its 

 development, and growers should be constantly 

 on their guard to prevent the spread and develop- 

 ment of diseases. 



"A system of crop rotation by which the land 

 will not be planted to sweet potatoes oftener than 

 every four or five years is the first step toward 

 disease control. Care in the selection and keeping 

 of potatoes intended for propagation is of impor- 

 tance, while clean cultivation and proper handling 

 at the time of harvesting are essential. Diseases 

 will generally make their first appearance upon cut, 

 broken, or bruised potatoes, and all that are in any 

 respect injured should be stored separately from 

 the seed and perfect stock. The storage house 

 should be cleaned and fumigated with sulphur or 

 formalin before storing begins, and all crates or 

 baskets used for handling the crop should be in the 

 house during the fumigation. 



"It is very apparent that some varieties are more 

 subject to the attacks of diseases than others. 

 The Big-Stem Jersey and the Jersey group gen- 

 erally are especially subject to disease, while va- 

 rieties of the Hay man group, such as Southern 

 Queen, are seldom affected. 



"The sweet potato is reasonably free from the 

 ravages of insects. Cutworms frequently destroy 

 the young plants after they are set in the field, 

 especially when the land has been in grass the 

 previous sea f son. The sweet-potato borer, which 

 works in the roots, is widely distributed and causes 

 considerable injury in the Gulf Coast States. A 

 small insect known as thrips works on the under 

 side of the leaves during the hot and dry weather of 



