JSTew York Agricultural Experiment Station. 231 



The field experiments of many writers indicate that formaldehyde 

 is as efficient as the mercury bichloride solution in killing potato 

 scab, but there are certain indications that make it appear doubtful 

 if such is actually the case. The difficulty with which formaldehyde 

 penetrates Rhizoctonia sclerotia, and its inability to kill certain 

 other fungi and the potato bacillus suggest that it may, sometimes, 

 be unable to reach and kill the scab organism which, according 

 to Lutman, 25 may be imbedded in the corky tissue of the scab 

 lesions. Also, since adsorption plays such an important role in the 

 formaldehyde gas treatment the efficiency would be least where 

 a large quantity of tubers was fumigated. Unfortunately, the 

 culture method can not be used successfully in determining the 

 efficiency of the treatment on scab. Although it is not difficult to 

 obtain pure cultures of the scab organism it does not grow on culture 

 media readily enough to make this method practicable. 



The results of this investigation, considered in connection with 

 those recorded in Bulletin No. 369, seem to warrant the following 

 conclusions: The disinfection of seed potatoes by means of formal- 

 dehyde gas is not to be recommended except in cases in which it is 

 impracticable to use either of the liquid treatments. When the 

 treatment is applied for scab alone either corrosive sublimate solution 

 or formaldehyde may be used; but when both Rhizoctonia and 

 scab are involved the corrosive sublimate solution is to be preferred. 



^Lutman, B. F. The Pathological Anatomy of Potato Scab. Phytopathology 

 3:261. 1913. 



