VEGETABLE AND FIELD CROPS 315 



but the roots grow very slowly and assume an abnormal, 

 narrow shape. The badly rotted hollow root may show 

 no external signs of the disease. 



The character, dissemination, and control of this disease 

 are discussed under cabbage. 



Club root. See cabbage. 



Powdery mildew {Erysiphe polygoni DC). — This pow- 

 dery mildew is often a serious pest in England, but seems 

 to be much less injurious in America, though it has fre- 

 quently been seen in this country, forming conspicuous 

 white patches upon the surface of the leaves. 



Macrosporiose (Macrosporium herculeum Ell. & Mart.). — 

 Numerous small, white spots occur upon the leaves, each 

 spot later with a slight, black, moldy growth in the center. 



Treatment is not warranted. 



Scab. See potato. 



White rust. See cabbage. 



Downy mildew. See cabbage. 



The two last-mentioned diseases often occur together 

 and in such form as to cause considerable loss. If plants 

 are badly affected, it is well to collect and burn all diseased 

 refuse and to rotate crops. 



WATERMELON 



Wilt, fusariose {Fusarium vasinfedum Atk. var. niveum 

 Sm.). — The melon wilt not only destroys the growing crop, 

 but prevents the successful culture of melons upon the field 

 in question in succeeding years. The disease has spread 

 rapidly during the past decade and is now known in most 

 of the southeastern United States ; also in Iowa, Oklahoma, 

 California, Oregon, Indiana, Kentuck}'^, and Arizona. 



