38 MASS. EXPERIMENT STATION BULLETIN 183. 



Exclusion of the Pathogexe. 



By exclusion we mean preventing a fungus from entering a given 

 territory in the first place, whether this territory be a country, a State, 

 a region or only one rose house. Since this disease seems to be pretty 

 generally distributed over the country already it is obviously impossible 

 to exclude it from the United States, and probably from any particular 

 State or section. But it is entirely possible to exclude it from the house 

 of a rose grower who finds that none of his plants are already affected, 

 or where new houses are being erected at some distance from old ones. 

 The whole practice, then, consists of taking every possible precaution 

 against carrying any diseased stocks, cuttings or infested soil into the 

 house. Every plant brought in should be carefully examined, and, if 

 there are any suspicious cankers in the bark, it should be discarded. All 

 new plants and cuttings should be taken whenever possible only from 

 houses known to be free from the disease. 



Eradication of the Pathogene. 



By eradication we mean the absolute destruction or removal of the 

 fungus from the rose beds or from the whole house, so that it is no longer 

 present in the plants or in the soil, pots, debris, manure or anywhere 

 else from which it can return to the plants. The practice of this method 

 is .of course necessary only when it has been impossible to exclude the 

 pathogene and it has become established in the house. Up to the present 

 this has proved to be the most successful principle applied to controlling 

 canker. 



The ultimate aim is to eradicate the fungus from the plant itself, but 

 the application of direct methods, such as excision of cankers, pruning 

 off of dead parts, or even absolute destruction of entire plants when 

 cankers are found on them, is altogether useless because the soil all about 

 the plants is infested. From the soil the fungus can grow back into 

 the roses as fast as it can be cut out. Spraying or dusting is of course 

 useless, also, because no fungicide can reach the mycelium in the inner 

 tissues of the plant; and also it is not possible to cover the parts of the 

 plant below the surface of the ground where infection commonly occurs. 

 Obviously, then, eradication resolves itself into destruction of the path- 

 ogene in the soil; in otlier words, soil disinfection. Of the various methods 

 of disinfecting soil only two have appeared to be at all practicable: (1) 

 by heat, and (2) application of chemicals. Freezing, as previously men- 

 tioned, is not effective. Desiccation would take entirely too long. Other 

 methods are either too expensive or too difficult of application. In the 

 course of the present investigation both heat and chemicals have been 

 successfully used. 



