PLUM DISEASES 367 



REFERENCES ON PLUM-GUMMOSIS 



Hedrick, U. P. Prunes in Oregon. Gumming of the prune tree. 



Oregon Agr. Exp. Sta. Bui. 45 : 68-72. 1897. 

 See further references to literature under Cherry, page 186. 



BLACK-SPOT 



Caused by Bacterium Pruni E. F. Smith 



This is a disease which occurs on the peach, apricot and nec- 

 tarine as well as the plum, and which is known as black-spot, 

 shot-hole, bacterial leaf-spot and bacterial-crack. Of all fruits 

 affected, plums show the greatest variation in susceptibility of 

 varieties. The larger part of American plums suffer but little, 

 whereas Japanese varieties, especially Abundance and Burbank, 

 are severely injured. The Chabot and Red June are among 

 other susceptible varieties. The more resistant plums include 

 Arkansas, Clifford, Cumberland, Diamond, Damson, Lombard, 

 Wild Goose and Yellow Egg. 



Black-spot of plums has been noted in various sections of 

 eastern United States during the past ten or twelve years. 

 It was first observed in Georgia in 1904, in Nebraska and 

 Missouri in 1906, in Delaware in 1907, and on Long Island 

 about 1908. Subsequent records have been made east of the 

 Mississippi River. 



The leaves (Fig. 106), fruits (Fig. 107) and twigs are diseased. 

 The leaves show a spot in which the tissue is brown and dead 

 (Fig. 106). Soon the affected portion falls away, leaving a shot- 

 hole. The holes are comparatively large and irregular in out- 

 line (Fig. 106). In severe cases premature defoliation occurs. 

 Fruits of susceptible varieties are badly distorted and cracked, 

 and are thus rendered liable to rot-producing organisms. Black 

 spots are developed thereon (Fig. 107). On plum-twigs it is 

 characteristic for the black spots to persist from year to year, 



