Diseases of the Sweet Potato 157, 



potatoes, but probably for several years. For that rea- 

 son, sweet potatoes should not be planted on the same 

 ground oftener than once in three or four years. It is 

 very doubtful whether that length of time will com- 

 pletely eradicate the fungus, but it certainly will 

 greatly reduce it. No other crops are known to be 

 attacked by the stem-rot fungus; therefore, any crops 

 commonly grown in the region may be used in the ro- 

 tation. 



It is important that all seed potatoes and commer- 

 cially grown draws should come from reliable dealers 

 and accompanied by a certificate stating that the po- 

 tatoes or draws are free from all serious diseases. 



Control of stem-rot. 



As has already been pointed out, the fungus invades 

 the potato. Consequently if diseased potatoes are 

 bedded out, diseased sprouts or draws may be expected, 

 as the fungus will pass from the tuber to the stem of 

 the young plant. In the early stages these diseased 

 plants are hard to detect, and many will be set out in 

 the field where the growth of the fungus will continue. 

 In the spring the seed potatoes should be disinfected 

 just before bedding by treating for five to ten minutes 

 in a solution made by dissolving 1 ounce of corrosive 

 sublimate in 8 gallons of water. Only wooden ves- 

 sels should be used for disinfection. Corrosive sub- 

 limate is a strong poison and should be kept out of the 

 reach of animals. After the potatoes are disinfected 

 they should be rinsed in pure water and laid in the 

 sun to dry. This treatment will not kill the stem-rot 

 fungus within the potato, but it will destroy any spores 

 that may be on the surface. The solution of corrosive 



