348 



Jourrial of Agricultural Research 



\'ol. VI, No. 10 



METHODS OF CONTROL 



Melhus (7) found in laboratory experiments that neither double 

 strength of mercuric chlorid (1:500) nor formalin applied for longer 

 than the ordinary periods would completely inhibit the development of 

 5. atrovirens on the potato and that both injured the tubers to such an 

 extent that germination was decidedly inhibited. He also found that 

 in many cases sporulation was inhibited on the surface of infected tubers 

 treated with solutions of mercuric chlorid heated by a method devised 

 by him for heating the solution for brief periods at temperatures near 

 the thermal death point of protoplasm. 



In view of these results, field tests were conducted during 191 4 and 

 1 91 5, both in Maine and at Norfolk, Va. Infected tubers were treated 

 in double strength and heated solutions of mercuric chlorid. In Maine 

 the treated tubers were planted on virgin soil. 



As noted in Table I, the temperature fluctuated slightly, owing to the 

 lower temperature of the tubers than that of the solution in which they 

 were immersed. This table indicates that there was a decrease in the 

 percentage of infected progeny in the treated rows as compared with the 

 check. However, in no case was there a complete control of the infection. 

 Similar tests in 191 5 also indicated that even though silver-scurf may be 

 inhibited to some extent; nevertheless, no treatment served as a complete 

 control. 



Table I. 



-Effect of warm sohition of mercuric chlorid on silver-scurf of the Irish 

 potato 



In October, 1914, four pecks of tubers infected with S. atrovirens were 

 subjected to a i to 1,000 solution of mercuric chlorid ranging from 45° 

 to 53° C. for four minutes with a view of ascertaining the effect of treat- 

 ing infected tubers with that solution before storing. After treat- 

 ment the tubers were placed in new muslin peck sacks and part of the 

 lot stored at Caribou and part at Washington. At the same time sepa- 

 rate lots of untreated infected and clean tubers were stored. On exami- 



