BIvACKI^EG. 323 



The introduction of small quantities of living, beef-broth 

 cultures into tubes of sterile water containing formaldehyde 

 or corrosive sublimate killed the germs, although the percentage 

 of the two germicides used was many times less than that of the 

 disinfection solution later recommended, and the exposure 

 being for a much shorter period. The germs introduced into 

 control tubes of pure sterile, distilled water at the same time 

 were not killed. 



The fact that the organisms are readily killed by drying and, 

 as already stated, fp. 317), no disease was produced by spray- 

 ing smooth seed tubers with vigorous active culture and allow- 

 ing them to dry several days before planting indicates that the 

 germs are probably not carried over on the surface of the 

 tubers. Very likely they live over winter in wounds or cracks 

 in the seed tubers or in small decayed areas, there being suffi- 

 cient moisture to keep them alive but the temperature of stor- 

 age is low enough to arrest their active development till after 

 the tubers are planted and begin to put forth shoots. 



Hence as a means of prevention: First, select seed, if pos- 

 sible, from fields upon which the disease has not appeared. 

 Second, discard for seed purposes all tubers which have 

 wounds, cracks or decayed areas*. Third, disinfect all seed 

 tubers with corrosive sublimate or formaldehyde before cut- 

 ting. Spreading the seed tubers out in thin layers in a clean, 

 dry place exposed to the direct rays of the sun for several days 

 would be an excellent supplementary practice and tend to has- 

 ten germination as well. The disinfection of seed tubers and 

 the rejection of all such as sho.w blemishes or diseased areas 

 will not only prevent the spread of blackleg but also the propo- 

 gation and spread of scab and most other tuber diseases which 

 attack the potato in Maine. 



Methods of Disinfecting Seed Potatoes. 

 , For disinfecting seed tubers for blackleg the same methods 

 are recommended as for potato scab. Either of the following 

 may be used. 



* This sorting out of the diseased tubers should alwaj's be done as 

 far as possible before cutting on account of possible contamination of 

 the freshly cut, moist surfaces of healthy seed pieces by germs carried 

 by the hands or knives used in cutting those tubers where the diseased 

 areas extended below where the disinfecting agents penetrated. 



