Diseases of the Potato 197 



the western United States, "spreads rapidly in potatoes 

 in transit to market or stored under unfavorable condi- 

 tions." None of these dry rots is known to affect the vine 

 to any extent. The fungi causing them will live in the 

 soil and infect the new crop when an opportunity comes, 

 so that in control all rotted tubers should be discarded 

 for planting. 



Silver scurf 



This is caused by the fungus Spondylocladium atro- 

 virens, recently introduced from Europe, and has been 

 commonly observed in the United States. It shows as 

 dark spots or areas on the surface of the tuber. In these 

 areas fine black points are found which make up the spore- 

 bearing area. The fungus destroys the skin so that the 

 moisture escapes and the affected tuber shrinks badly. 

 The affected areas at this time and even before have a 

 silvery luster, a character which gives the disease its 

 name. The market value of such tubers is lessened, and 

 they should not be used for planting, as seed treatment 

 is apparently ineffective in destroying the fungus. 



Potato wart 



This disease, caused by one of the lower forms of 

 fungi called Synchitrium endobioticum, does not appear in 

 the United States and should continue to be kept out by 

 strict quarantine measures. The disease has been known 

 in Hungary since 1896. It has been found in many 

 European countries and also in Newfoundland. It is 

 reported to be very destructive and is very difficult to 

 control, a long rotation of crops being the only measure 

 recommended. 



