780 Popular Editions of Station Bulletins of the 



the Rhizoctonia sclerotia were much more completely destroyed on 

 tubers that had been put into the fumigator when wet. 



Soaking the tubers in formaldehyde solution was 

 Liquid no more effective in destroying the Rhizoctonia 



disinfection. sclerotia than was fumigation unless the time of 



immersion was long or strength of solution increased 

 above that usually recommended. In eight tests with a l-to-240 

 solution and a two-hour immersion almost one-fourth of the sclerotia 

 grew in the cultures, but when the time was increased to 24 hours 

 all were destroyed, as they were also when the strength of solution 

 was made l-to-20 and the time was 2 hours. 



In corrosive sublimate solution, however, even as low strength as 

 l-to-2000, the sclerotia were destroyed by less than a 2-hour 

 treatment. 



The scab-fungus spores and mycelium are probably less resistant 

 to fungicides than these Rhizoctonia sclerotia, but this series of 

 tests casts considerable doubt upon the efficiency of the treatment 

 with formaldehyde gas for scab; while it surely cannot be relied 

 on to prevent the transmission of Rhizoctonia. 



It seems best, therefore, to advise potato growers who 

 General wish to disinfect the tubers they use for seed, to 



conclusions. use the gas treatment only in cases where it is 



impracticable to use either the liquid formaldehyde 

 solution or corrosive sublimate. The safety and efficiency of 

 both the liquid treatments for scab have been thoroughly estab- 

 lished, while the evidence just given proves the gas treatment unre- 

 liable for controlling Rhizoctonia and casts considerable doubt on 

 its effectiveness against scab. When it is desired to treat potatoes for 

 both Rhizoctonia and scab the corrosive sublimate solution should 

 be used; but in treating for scab alone the formaldehyde solution is 

 effective, while the corrosive sublimate solution, though effective, is 

 in many ways less desirable to use. 



The method to be used in applying any one of these 

 Directions treatments is summarized in the following para- 



for using graphs, which should be carefully read before begin- 



treatments. ning the work. 



Formaldehyde gas. — Use a thoroughly tight, un- 

 heated room. Place the seed tubers in shallow, slatted crates, not 

 over eight inches deep, and so arranged that the gas may circulate 

 freely on all sides of the potatoes. For each 1,000 cubic feet of 

 space in the disinfection room use three pints of formaldehyde (40 

 per ct. solution) and 23 ounces of potassium permanganate (slender, 

 needle-shaped crystals). Spread the potassium permanganate over 

 the bottom of a large pan or pail having a capacity equal to about 

 one quart for each ounce of permanganate. Pour on the formalde- 

 hyde, close the door at once and keep it closed for 24 hours. It is 

 important that the disinfection room contain approximately 10 lbs. 



