253 

 PLUM LEAF-BLIGHT (Cylindrosjjorium padi Karsten.) 



The plum leaf-blight in western New York, aside from giving much 

 trouble to nurserymen, does very great damage to many varieties of 

 bearing trees, defoliating them in August and September. This disease 

 is considered -by the plum-growers in the vicinity of Geneva as their 

 most persistent enemy. A large orchard belonging to E. Smith & Sous, 

 2 miles northwest of the city, was, they informed me, winter-killed 

 about thirty years ago because of defoliation the summer previous. It 

 is a common opinion among orchardists that leaf-blight, through its 

 retarding effect upon the maturation of the wood, renders the trees 

 incapable of withstanding the changes in temperature of a trying win- 

 ter. Whatever the explanation of this fact may be, it seems self-evi- 

 dent that a tree which drops its leaves before the normal season suf- 

 fers very material loss. 



Of nursery stocks, the native-grown seedlings suffer the most from 

 this disease, often losing all their leaves by the middle of August. My- 

 robolan and Marianna stocks are not to any extent subject the first 

 season. In entire contradistinction to the immunity exhibited by 

 pear " buds " which resist to a remarkable degree pear leaf-blight, the 

 budded plum stocks are particularly susceptible to pluni leaf-blight. 

 Apparently the same conditions of rapid growth which afford immunity 

 in the one case tend to susceptibility in the other. The two instances 

 offer a fertile field for inquiry. 



The experiments on this disease were made with Bordeaux mixture 

 and ammoniacal solution upon two rows of stocks, one of Mariajina, 

 containing 504 stocks, and the other of Myrobolan, containing 474 

 stocks. As described previously * the results of the first season's ex- 

 periment were entirely negative, as the disease failed to appear. 



On October 9 the three varieties, Early Prolific (Early Elvers), Pur- 

 ple Egg (Hudson Kiver Purple Egg), and Italian Prune (Fellenburg), 

 were budded upon both rows of stocks as set forth subsequently, p. 258. 

 Numerous stocks were left unbudded to test the effect of the fungicides 

 and the end of each row was left untreated. 



The rows were treated in 1802 with Bordeaux and ammoniacal solu- 

 tion, the formula of which are described on p. 262. One-half the 

 treated stocks received 5 sprayings and the other 6, at the dates given 

 on p. 243. In all respects the two rows were treated alike. 



MYROBOLAN STOCKS. 



1892. The disease made its first appearance in June upon the un- 

 budded stocks which were carried over from 1891, and strangely 

 enough only upon the treated portions. This dropping of the treated 

 Myrobolan foliage was confined to the leaves situated on the larger 



* Bull. No. 3 Div. Veg. Path., p. 58. 

 16486 No. 3 5 



