130 THE PLUMS OF NEW YORK. 



prevention or cure are not established though all agree that soils may be 

 inoculated with the disease from infected stock; hence the necessity of 

 discarding diseased trees at transplanting time. 



Smith fotmd in Michigan and Clinton in Connecticut a disease of the 

 fruit called bacterial black spot' (Pseudomonas pruni Smith) of the same 

 generic origin as the crown gall but widely different in nature. The writ- 

 ers and the growers who found the infected fruit, saw the disease only on 

 the Trifiora plums. It attacks the green fruits which show conspicuous, 

 black-purple, sunken spots sometimes as large as half an inch in diameter. 

 The injuries are usually isolated and quite superficial but nevertheless, 

 spoil the fruit. 



The plum in common with other stone-fruits often stiff ers from an 

 excessive flow of gum, for which trouble the name gummosis ' is now 

 generally applied. The disease is to be found wherever pltmis are grown 

 but it is much more destructive on the Pacific than on the Atlantic sea- 

 board. So far as is now known gummosis is secondary to injuries caused 

 by fungi, bacteria, insects, frost, sunscald, and mechanical agencies. The 

 disease is least common in species and varieties having hardwood; on 

 trees on soils favoring the maturity of wood; under conditions where 

 sun and frost are not injurious; and, obviously, in orchards where by 

 good care the primary causes of gumming are kept out. Stewart ' has 

 recorded an interesting case of gum-pockets in the fruit, but could assign 

 no cause. 



Mechanical injuries from the sim, frost and hail are troubles with 

 which nearly all plum-growers must contend at one time or another. In 

 this region the Reine Claude and Trifiora plums suffer much from sunscald 

 but none are wholly immtine, though Lombard is possibly most so. These 

 injuries from the elements of weather are often mistaken for diseases, 

 and are so often followed by fungal parasites and insects as to make it 

 difficiilt to distinguish the primary from the secondary trouble. Low- 

 heading of the trees is the best preventive of these tnmk injuries. 



Plvims are somewhat subject to attacks of the well-known peach 

 scab * (Cladosporium carpophilum Thumen). The scab appears in numer- 

 ous, small, sooty, circular spots of brownish color, often confined to one 



' Smith, E. F. Science 17:456-7. 1903. Ibid. 21:502. 1905. Clinton, G. P. Report of Botanist 

 Conn. Sta. Rpt. 273. 1905. 



' Hedrick, U. P. Gumming of the Prune Tree Oreg. Sta. Bui. 45:68-72. 1897. 



•Stewart, F. C. N. Y. Sta. Bui. 191:324-326. 1900. 



♦ Pammel, L. H. New Fungous Diseases of Iowa Jour. Myc. 7:99-100. 1892. 



