Diseases of the Sweet Potato 159 



dried out In the seed-bed, the young sprouts shrivel 

 and turn black near the surface of the ground extend- 

 ing a few inches up the stem. The young draws look 

 weak and discolored and finally die in severe cases. 

 The tubers are usually attacked from one end and 

 shrivel and dry up, the disease gradually working back 

 toward the other end. 



Foot-rot is distributed in the same way as stem-rot 

 and black-rot, through diseased soil, exchange of plants 

 or seed potatoes, 



Fool^rot is known in Virginia, Iowa, and Missouri, 

 and it is probable that it occurs* elsewhere. 



Owing to the fact that it is not so widely distrib- 

 uted, the total loss that may be attributed to this disease 

 is much less than with black-rot and stem-rot. In lo- 

 calities where it does occur, however, it produces 

 greater loss than either of those diseases. In certain 

 sections of Virginia, Ohio, and Iowa, it has been esti- 

 mated to produce a loss of 50 per cent of the crop in 

 one year. 



The same control measures should be applied for this 

 disease as for stem-rot and black-rot : — namely, seed 

 selection, clean seed-beds, and crop rotation. 



EGOT-EOT (Plate VII) 



(Ozonium omnivorum) 



This disease is best known as the Texas root-rot of 

 cotton and alfalfa. The causal organism gains access 

 to the plants on the underground parts and spreads in 

 both directions, invading the vines for 6 to 12 inches 

 above the ground. It may enter the potato at the end 

 or form lesions of varying sizes on the surface. In - 



