368 MANUAL OF FRUIT DISEASES 



forming perennial cankers. Thus old neglected trees are par- 

 ticularly a constant source of trouble and danger to other trees. 

 These cankers are relatively large and deep on the Abundance 

 and Burbank varieties. Cankers on the plum are somewhat 



$ different in appear- 



ance from those on 

 the apricot, necta- 



^ jf k ^^ J t, ^|fe r i ne an d peach. 



Open cankers are the 

 more common type 

 observed on the last 

 three fruits, whereas 

 on the plum the af- 

 fected bark clings to 

 the twig for some 

 tune. Watersprouts 



FIG. 107. Black-spot on plums ; developmental of plums may at 



stages. ,. 



tunes show twenty 

 or more cankers in various stages of development. 



See more complete account of Black-Spot under Peach, 

 page 306. 



REFERENCES 



Jackson, H. S. Bacteriosis of plums. Delaware Agr. Exp. Sta. 



Ann. rept. 16-18 : 75-76. 1907. 

 Lewis, I. M. A bacterial canker of plum twigs. American Micros. 



Soc. Trans. 31 : 145-149. 1912. 

 (Additional references to literature under Peach, page 311.) 



SILVER-LEAF 

 Caused by Stereum purpureum Fries 



While this disease has not been observed with certainty on 

 plums in the United States, it is known on apple, and its preva- 

 lence and destructive nature in Canada and elsewhere would 



