1911.] PUBLIC DOCUMENT — No. 31. 167 



disease, it apparently resembles in outward appearance very 

 much the spotting that I described as due to the brown rot 

 fungus.^ 



Peach Leaf Curl {Exoascus deformans (Berk.) Fuckel). 



This disease is found commonly in Massachusetts, and, as a 

 matter of fact, more inquiries are sent to the station in regard to 

 this trouble than any other peach disease. It is found in almost 

 all parts of the world where the peach is grown to any extent, 

 and has been seen by the writer in great quantities in the large 

 orchards along the shores of Lake Erie. 



It attacks the leaf buds just as they begin to open in the 

 spring, also the tender shoots, flowers and young fruit, but is 

 not so noticeable as on the leaves. The leaves become very 

 much swollen, wrinkled and curled, and a little later take on 

 the appearance of a moldy gray covering. In the earlier stages 

 of the disease the leaves often show red or pinkish blotches, but 

 they turn a brownish color as they grow older and fall to the 

 ground. Cold and damp, or rainy, weather in the spring 

 greatly favors this disease, and in fact determines the degree 

 of severity of the attack. It often defoliates the trees to such 

 an extent that they are not able to lay up sufficient material for 

 their needs, or ripen the wood properly, so that when winter 

 comes the trees are often found to be much weakened. In some 

 cases the disease has been so severe that the trees were not able 

 to endure the cold of winter, and consequently were winter 

 killed. 



It was previously thought that infection took place only by 

 perennial mycelia, but this theory has gradually been discarded. 

 Infection may take place by perennial mycelia, but most writers 

 and observers now agree that infection is due almost entirely to 

 the spores, which live over winter on the bark of trees and in 

 other places. 



The Elberta peach is one of the most susceptible varieties to 

 the attacks of this fungus, but all varieties seem to be more or 



' For other points of interest in regard to tlie fungus not given in this paper see Arthur's and 

 Chester's writings. 



