204 MAINE AGRICULTURAL EXPERIMENT STATION. I9II. 



favorable conditions of temperature and moisture if they come 

 in contact with the interior tissues. Therefore, there is no 

 doubt that some of the soft rot in storage may come from this 

 source. It is also evident that diseased plants only spring from 

 tubers produced by previously diseased plants, or from tubers 

 infected in storage or while being cut for seed purposes. by com- 

 ing in contact with those already diseased. 



So long as Maine growers confined their efforts to the pro- 

 duction of table stock, blackleg was not one of the more im- 

 portant potato diseases and attracted little attention. When 

 the value of northern-grown potatoes for southern planting 

 began to be appreciated an entirely new situation developed. 

 The southern trade demanded early varieties, the favorite 

 among which is the Irish Cobbler which is much more suscep- 

 tible to the blackleg disease than the Green Mountain and cer- 

 tain other, late varieties commonly grown for table stock. 

 Moreover blackleg appears to be much more destructive in Vir- 

 ginia and other southern States, where most of the seed tubers 

 are sold, than in Maine. Consequently from the standpoint of 

 the seed potato trade this disease has become one of consider- 

 able importance. If Maine seed potatoes for southern planting 

 are to retain the place that their various superior qualities have 

 secured for them it is absolutely essential that this disease be 

 eliminated from among them. In other words, from a financial 

 standpoint this is the most important disease problem that the 

 seed potato growers are facing at the present time. It is be- 

 lieved that the experiments here reported demonstrate that any 

 farmer can entirely eradicate the disease from his seed and 

 from his farm in from one to 2 years and that so long as he 

 kee"ps this seed pure and uncontaminated he may feel assured 

 of immunity from blackleg. 



Pre;liminary Expe^ri mental Work. 



After isolating the bacteria associated with the disease in 

 Maine and demonstrating by inoculation that they were capable 

 of causing the typical blackening and decay of the stem as well 

 as the soft rot of the tuber the first matters to determine before 

 attempting to devise methods of control were the resistance o.^ 

 the organisms to drying, to expi sure to sunlight, and to disin- 



