ROSE CANKER AND ITS CONTROL. 45 



begun for something more suitable. Up to the present, lime gives the 

 best promise of making a satisfactorj^ barrier. Sterile bottle tests show 

 that the mycelium will not grow in soil containing air-slaked lime at 

 the rate of 1^ pounds per cubic foot. Neither will spores germinate in 

 the presence of lime. Until something more satisfactory is found it is 

 recommended that all walks in the houses be kept covered with lime. 

 Not only will this furnish an effective barrier to the fungus coming up 

 from below, but it will also prevent growth of spores and other inocula 

 brought in from other houses on the shoes of workmen and visitors. 



Immunization of the Host. 



By immunization we mean either the development of varieties of roses 

 which are immune, — at least highly resistant, — or rendering them 

 immune by injection or feeding through the roots with some chemical. 

 No work has been done along either of these lines in regard to rose canker. 

 From the first it has been noticed that some varieties of roses are more 

 susceptible than others. No doubt in the course of time desirable varieties 

 will be found or developed which will not suffer from canker. How soon 

 that will be no one can predict. A rose breeder of wide national reputa- 

 tion told the writer that he had spent most of his life producing four or 

 five varieties of roses. It is a long process, and until such varieties are 

 developed it will be necessary to resort to such emergency measures as 

 have been described in this bulletin. 



Summary of Control Measures. 



In the light of all that we know about rose canker and its causal path- 

 ogene the following measures are recommended for its control : — 



1. Carefully inspect the rose house to see if canker is present. If 

 not, employ every means to prevent its entering, — import as few roses 

 as possible from other houses; examine carefully every plant brought in; 

 reject any with suspicious dead areas in the bark. 



2. If it is present on the roses it cannot be eradicated from the infected 

 plants. The only hope lies in starting new plants from clean cuttings in 

 clean soil, and guarding against infection at every step in the plant's 

 development. 



3. Dip the cuttings in Bordeaux mixture. 



4. Sterilize the pots by dipping for ten minutes in boiling water. 



5. Sterilize the potting soil and cutting bench soil by steaming to a 

 temperature of over 50° C. for ten minutes or more. Suspected manure 

 should be treated in the same way. 



6. Use raised benches, not ground beds. 



7. Remove old soil if diseased roses have been grown in it, and soak 

 the benches thoroughly with (1) formaldehyde at the rate of 1 pint to 

 25 gallons, or (2) boiUng water. 



