294 DISEASES OF ECONOMIC PLANTS 



The chief loss is in the cessation of growth resulting 

 from the disease. In badly infected fields no potatoes 

 of marketable size mature, and the crop is not worth 

 harvesting. 



Long rotation to avoid placing sweet potatoes upon 

 infected soil is advised. 



Halsted ^ shows that soil rot, even upon land badly in- 

 fected with the fungus, can be controlled by sulphur and 

 kainit ; 400 pounds of each applied to the soil when the new 

 roots are to form gave the best results. Treated plats 

 gave 60 bushels of clean potatoes as contrasted with 5 

 bushels for the untreated plat. 



Wilt, stem rot, nectriose {Nectria Impomcece Halst.). — 

 In this disease, reported from New Jersey, California, 

 North Carolina, Ohio, and Illinois, the stem dies near the 

 surface of the ground, and the decay extends into the pota- 

 toes and vines. The whole vine dies unless supported by 

 roots at some other place. Following the dea^h of the 

 original stem, the portion of the root still alive throws out 

 a fresh growth of short stems and leaves near the center of 

 the hill. Such efforts at recovery are valueless. 



Rotation is necessary. 



Dry rot (Phoma Batatce (Ell. & Halst.). — In dry rot, 

 the affected part, often the upper end of the potato, 

 becomes dry, much wrinkled, and covered with numerous 

 pycnidia, the flesh within changing to an almost powdery 

 condition. From an economic point of view the rot is 

 unimportant ; still, affected potatoes should be destroyed. 



Dry rot, lasiodiplodiose (Lasiodiplodia tuhericola Ell. & 

 Ev.). — The. potatoes show dark, shriveled patches with 



1 Halsted, B. D., N.J. Agr. Exp. Sta. Rpt. 1898, 350. 



