CONTROL OF BLACKLEG DISEASE OF THE POTATO. 221 



upon to throw away all tubers which show, diseased areas in 

 the interior to which the disinfecting agent could not possibly 

 penetrate. 



That formaldehyde gas generated by means of potassium 

 permanganate is exceedingly efficient in killing the germs of 

 many contagious diseases of man, which are much more resist- 

 ant than the bacteria associated with the blackleg disease of 

 potatoes, is well known. Moreover it has been shown that for 

 a surface disinfectant of potatoes for scab formaldehyde gas 

 generated in this way and by simple evaporation of the concen- 

 trated liquid by heat gives as good results as the ordinary meth- 

 od of soaking the seed tubers in dilute formaldehyde solution.* 

 The method recommends itself for practical work on account of 

 its apparent simplicity and the ease and rapidity by which dis- 

 infection can be accomplished by its use. However, its use in 

 the hands of practical farmers develops certain fundamental 

 difficulties which are not present when the liquid method of 

 treatment is used. There is very little opportunity or excuse 

 for one to fail to follow directions in the case of the latter. 

 It was found in these experiments and in others where the 

 formaldehyde-permanganate method of gaseous disinfection has 

 been used for potato scab that it was almost impossible to get 

 the men in charge of the work to comply with all of the require- 

 ments necessary. Frequently the rooms used for the purpose 

 are too cold and no provision is made for a moist atmosphere. 

 There is also a tendency to pile the tubers too deep in the crates 

 and to place the crates too close together and too close to the 

 wall to allow for complete circulation and penetration of the 

 gas to all parts of the surface. of each and every potato. Where 

 the tubers are immersed in the dilute formaldehyde solution for 

 2 hours there is a certainty that the entire surface of each potato 

 comes in contact with some of the disinfecting agents. 



Blackleg Not Carried Over in the Soil in Maine. 



Field observations extending over 5 consecutive years have 

 failed to reveal a single case where there was any evidence to 



* Jones, L. R. and Morse, W. J., Repts. Vt. Exp. Sta. 16: 165-168 

 (1903), 17: 397-402 (1904), 18: 287-291 (1905). Morse, W. J., Potato 

 Diseases in 1907, Bui. Me. Exp. Sta. 149: 304-316 (1907). 



