DISEASES AND INSECTS 



299 



while the potatoes are curing. As long as moisture condenses during 

 cool nights on the roof or walls of the warehouse, good ventilation 

 should be provided, but when the potatoes have been well cured, the 

 house may be shut up reasonably tight, and they will generally keep 

 for several months. Disturbing the potatoes causes them to rot, 

 so that a bin should be marketed as soon as it is opened. 



FIG. 122. Sweet potato affected with black rot, and plant affected wi.th same disease. 

 (After Halstead, New Jersey Bulletin 76.) 



Diseases and Insects. The sweet potato is quite free from 

 injurious diseases and insects. The most destructive disease is 

 known as black rot. Black rot (Fig. 122) gives some trouble in 

 the field, but is most injurious in the warehouses. It appears as 

 rather large black spots on the potato, soon causing the rot. The 

 principal method of control is to provide against infection in the 

 field. It is usually carried over in the soil or on the plants. Great 

 care should be taken to use seed free from the disease. For this 

 reason many growers use seed grown from slips, planting it in soil 



