114 THE AMERICAN APPLE ORCHARD 



Sometimes the canker appears about the base of the 

 tree. In this form it is sometimes called collar rot. 

 There are certainly several diseases, closely related, 

 caused by different fungi, which may all be roughly 

 grouped under the name of canker. 



Different varieties of trees differ greatly in their sus- 

 ceptibility to canker. Tompkins King is especially vul- 

 nerable. Esopus Spitzenberg is another. Spy and Tol- 

 man are practically immune. In view of such facts 

 some enterprising growers are adopting the practice of 

 top-working varieties like King on trees like Spy. The 

 tree which is used for top-working in this way should 

 be allowed to form a good head before regrafting in 

 order that the crotches may be sound and free from 

 cankers. 



Pruning and spraying with general good treatment 

 is the preventive, and to some extent a practical 

 remedy, for canker. The cankered branches should be 

 cut out and burned, as far as possible. Where there 

 are large branches which cannot be spared but which 

 have canker spots, these spots should be scraped, pared 

 down to healthy wood and painted with a heavy coat 

 of thick white lead paint. Thorough spraying with 

 bordeaux kills the spores of the canker fungi ; and an 

 orchard carefully sprayed every year, a'fe spraying is 

 done for the scab fungus, will never suffer from 

 canker, unless it be under the most exceptional circum- 

 stances. 



Bitter Rot The same fungus which causes one 

 form of canker causes also a disease of the fruit, 

 known as bitter rot. This disease is very destructive 

 some years in certain localities, especially in southern 

 Illinois and Missouri. In this neighborhood the entire 

 crop is. occasionally ruined. The rot appears on the 



