SILVEE SCURF, A DISEASE OF THE POTATO. 23 



heat on tubers infected with PJiytophthora infestans. Spondylocla- 

 dium fruited from 4 to 10 days after the tubers had been subjected to 

 50° C. for 2 to 10 hours. If the potatoes were kept at 50° C. for 

 longer periods their germmating capacity was injured. This tends 

 to show that the viability of the fungus is even greater than that of 

 its host. Experiments are in progress to determine further the 

 value of formalin as a means of controlling this disease. 



RELATION TO THE SEED-POTATO INDUSTRY. 



In order to gain some idea as to the amount of sUver scurf present 

 on potatoes being used for seed purposes tliis spring, several days 

 were spent examhihig the seed stock being planted m the vicmity of 

 Norfolk, Va. A shipment of over 500 barrels raised in northern 

 Vermont came to the writer's attention. These potatoes were shipped 

 to Norfolk last November and stored at a temperature rangmg from 

 40° to 65° F., accordmg to the statement of the owner. Some 

 Phytophthora rot was in evidence in tliis stock. The combmation 

 of high temperature and moist condition, the latter due to the soft- 

 rot, favored the development of Spondylocladium. Both the brown- 

 mold and the sclerotial stages were readily detected, especially the 

 former. Three barrels were sorted with the following results : 



First barrel (by measui-e), infection with silver scurf 40 per cent. 



Second barrel (by measure), infection with silver scurf 2 per cent. 



Third barrel (by measure), infection with silver scurf 50 per cent. 



It was impossible to examine every potato in any considerable 

 number of barrels, so 17 other barrels from the collection of over 

 500 were dumped separately and the amount of silver scurf estimated. 

 This was not especially difficult, because of the prevalence of the 

 brown-mold stage, wliich is quite conspicuous when well developed. 

 The amount of silver scurf ranged from about 1 to 90 per cent. 

 When the amount of soft-rot was great the percentage of silver scurf 

 was less, due, it is believed, to the excessive moisture present, a con- 

 dition unfavorable for the rapid spread of the fungus. In 10 of the 

 barrels exammed the amount of silver scurf ranged from 25 to 90 

 per cent and in the remauiing 10 it varied from about 1 to 25 per 

 cent. 



Another collection, consistmg of 25 ban-els of potatoes which had 

 just arrived from Ai'oostook County, Me., showed about 25 per cent 

 of silver scurf. It was strikingly noticeable in tliis collection that 

 the disease was not as far advanced as in the earlier collection ex- 

 amined, and only the sclerotial stage was in evidence. Still another 

 collection from Maine needs mention. It consisted of 15 barrels 

 grown in the south-central part of the State. This collection was 

 remarkably free from late-blight, but showed 35 per cent of silver 



[Civ. 127] 



