ROSE CANKER AND ITS CONTROL. 43 



in boiling water for ten minutes. Steaming is just as effective. The 

 method used is simply a matter of convenience. 



Usually a grower, when he finds disease in his houses, finds it imprac- 

 ticable to destroy all his roses and start all over again. Therefore he 

 retains some of his old houses and starts disinfection operations on one 

 or more, from which he has removed all the plants. This inevitably 

 results in the constant danger of carrying some infested soil or parts of 

 plants from the infested to the clean houses. Every possible precaution 

 should be taken to guard against this, because a failure here means that 

 the work must all be done again. All sorts of tools offer an easy means 

 of conveying the inoculum. Whenever possible an entirely different 

 set of tools should be used in the clean houses, and no tools from the 

 other houses brought in under any conditions. But, if this is not possible, 

 the next best alternative is to sterilize the tools before bringing them in. 

 The method of sterilizing them is not so important as thoroughness. 

 They may be dipped in boiling water, steamed, or a barrel of Bordeaux 

 mixture or formaldehyde — preferably stronger than 1 pint to 25 gallons 

 in this case — may be used for soaking the tools. 



It may be necessary to sterilize other things besides pots and tools, 

 e.g., boots and clothes of workmen. Every grower, after learning the 

 habits of the pathogene, must decide for himself on the best way, under 

 his own conditions, of keeping his houses clean. 



Protection of the Host. 



By protection we mean the placing of a barrier between a plant and 

 a pathogene which would otherwise attack it and cause disease. This 

 is well exemplified in the extensively used practice of spraying plants, 

 the fungicide forming a poison barrier through which the fungus cannot 

 penetrate. The humicolous habit and underground method of attack 

 of the canker fungus seem to preclude anj'^ hope of important benefit from 

 spraying. There is one place in the propagation of roses, however, where 

 a fungicidal covering might be beneficial. Scions and cuttings should, 

 whenever possible, be taken from houses known to be clean. If they 

 are taken from houses in which the disease occurs there is always a 

 possibiUty of spores being lodged on them, even where lesions have not 

 as yet appeared. To either wash off and kill these spores or, at least, to 

 prevent germination where they are, it has been the practice during this 

 investigation to dip all such cuttings in a fungicide before grafting or 

 planting. 



Comiparative Valiie of Different Fungicidal Coverings. 

 In order to find the best fungicide to use for dipping, and also to secure 

 data for use in case spraying should be found advisable at any time, the 

 comparative value of a number of fungicides was tested in the laboratory. 



