VEGETABLE AND FIELD CROPS 289 



corresponding upper surfaces, indicate the downy mildew. 

 The disease in its habit and damage resembles that of the 

 grape, p. 166. 



Serious loss is reported from New Mexico and Virginia. 



Leaf blight, phyllostictose (Phyllostida Chenopodii Sacc). 

 — This disease affects the leaves, especially at their bases, 

 producing spots which bear minute pycnidia. 



Cercosporose (Cercospora heticola Sacc). — This disease 

 often ruins crops by yellowing and dwarfing the plants, 

 thus rendering them worthless for market. By causing 

 local leaf spots it diminishes the vigor of the plant. 



SQUASH 



Powdery mildew (Erysiphe cichoracearum DC). — This 

 mildew is very common upon the squash, forming the usual 

 whitish coating upon the' surface of the leaves and stems. 



Downy mildew. See cucumber. 



Wilt, bacillose. See cantaloupe. 



Anthracnose, coUetotrichose. See watermelon. 



SWEET POTATO 



Soft rot (Rhizopus nigricans Ehrbg.). — The most prom- 

 inent soft rot of the sweet potato, the only one that is 

 commonlj^ met, may be recognized by the soft, wrinkled 

 condition of the potato, its sweetish odor, and usually 

 by the presence of a white, later black, growth of mold, 

 appearing through the skin of the rotten portion at points 

 of rupture. 



The decay most often begins at one end and passes 

 rapidly through the root, but it may start at a wound upon 

 any part of the potato. It progresses with such rapidity 



