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A Bulletin on Orchard Practice 



BLACKSPOT CANKER. 

 BY W. H. LAWRENCE. 



Blackspot Canker is a disease of the apple tree. In im- 

 portance it ranks next to the apple scab. It is very prevalent 

 and destructive in Western Washington in localities where the 

 rain-fall is considerable during the latter part of autumn and 

 early winter. The disease is caused by a parasitic fungus 



CANKER PATCHES on Apple Tree Branches. 



The fungus lives in the bark for about a year and then dies. 

 Before it dies it forms spores the greater number of which are 

 distributed from October to late December or a little later. 

 These spores are carried about by the wind and some of them 

 lodge on the bark of apple trees. The moderately low tem- 

 perature and plenty of moisture usually present in November 

 and later are conditions most suitable for germination. On 

 germinating the fungus enters the bark. Occasionally by the 

 end of a week new cankers make their appearance, They are 

 about the size of a pin head, circular, somewhat sunken, and 



