POW'DERV SCAB OF POTATOES. IO3 



tion has been given to this subject and some phases of it have 

 not been touched at all. However there is available a large 

 amount of data regarding the effects of certain disinfectants 

 like formaldehyde and corrosive sublimate used for treating 

 seed tubers for common scab, blackleg, Rhizoctonia, etc. The 

 conclusions derived from this, taken in connection with the 

 work of Pethybridge on powdery scab in Ireland, may serve as 

 a tentative basis for recommendations as to disinfection, in 

 the absence of any experimental results obtained in this country. 



Formaldehyde, sometimes called formalin, as ordinarily used 

 is perfectly safe to handle. A large number of trials by dif- 

 ferent investigators have shown it to be fully equal to corrosive 

 sublimate for treating potatoes for common scab. The writer 

 has also found it to be efficient in the case of the blackleg dis- 

 ease. Corrosive sublimate is a very active poison and should 

 be handled with great care. It cannot be used in iron vessels 

 and tubers treated with corrosive sublimate should not be fe 1 

 to stock or left where animals can get at them. 



According to the recent work of Gloyer* corrosive sublimate 

 is much more efficient than formaldehyde in the treatment of 

 seed potatoes for Rhizoctonia in that it thoroughly penetrates 

 and kills the sclerotia of the fungus, while the latter does not. 

 Hence where both Rhinzoctonia and scab of either type are 

 present corrosive sublimate is to be preferred. It is also pos- 

 sible that the greater penetrating power of corrosive sublimate 

 claimed by Gloyer may make it more efficient for treating for 

 powdery scab. However until accurate experimental work 

 demonstrates the superiority of one over the other when used 

 against powdery scab it is impossible to say which is the most 

 effective with reference to this disease. The amounts of the 

 disinfectants to use and the length of time for treating seed po- 

 tatoes are as follows : 



Formaldehyde. 



Formaldehyde, 40 per cent i pint 



Water 30 gallons 



Soak tubers 2 hours in this solution. 



* Gloyer, W. O. The Efficiency of Formaldehyde in the Treatment of 

 Seed Potatoes for Rhizoctonia. Bui. N. Y. Agr. Exp. Sta. 370. 1913. 



