163 The Sweet Potato 



plied to black-rot as to stem-rot, particularly the prepa- 

 ration of the hotbed. If black-rot alone is concerned, 

 the seed may be selected in the spring instead of in the 

 fall. If selected in the fall, it should be picked over 

 again in the spring and any potatoes with suspicious 

 spots on them discarded. 



The treatment of the soil with sulfur, lime, gypsum, 

 or different fertilizers has little or no effect on the dis- 

 ease. Dipping the slips in a solution of bordeaux mix- 

 ture or in a lime-sulfur mixture just before setting 

 them in the field does not prevent the disease, but has 

 been found greatly to injure the plants. 



SCUEF (soil-stain, SOIL-SPLOTCH, EtTST, JEESET MAEk) 



Scurf is characterized by a brown discoloration of the 

 surface of the underground parts of the sweet potato 

 plant. (Plates V, VII.) The discolored areas may 

 take the form of spots of varying sizes and shapes with 

 no definite outline or there may be a uniform rusting of 

 the entire surface of the potato. The scurf produces no 

 rupture of the sweet potato and is so superficial as to 

 be scraped off easily by the finger-nail. 



Scurf is widely spread over the sweet potato area. 



To control this disease, the seed potatoes should be 

 disinfected for ten minutes in a solution made by dis- 

 solving 1 ounce of mercuric chlorid (corrosive subli- 

 mate) in 8 gallons of water. They should then be 

 dipped in water and dried. Soil or sand obtained from 

 the woods or from fields where sweet potatoes have never 

 been grown should be used in the hotbed. The plants 

 should be set in new ground or ground never before 

 employed for sweet potatoes. 



Scurf is worse on heavy soils and on those contain- 



