226 FUNGOUS DISEASES OF PLANTS 



XXIV. MILDEW OF APPLE AND CHERRY 



Podosphara Oxyacanthce (De C.) De Bary 



Fairchild, D. G. Experiments in Preventing Leaf Diseases of Nursery 

 Stock. Journ. Mycology 7: 256. 1894. 



This fungus is common on a large number of rosaceous and 

 other plants, including apples, plums, thorn apples, etc. It may 



Fig. 91. Sphmrotheca Humuli on Cultivated Strawberry 

 (Photograph by E. H. Favor) 



be considered as a destructive disease in this country chiefly as 

 it occurs upon apple nursery stock or upon the cherry (Fig. 92). 

 Upon the young apple plants the mycelium is rather dense and 

 persistent. Perithecia are from 65 to 90 fj. in diameter and the 

 appendages, from 4 to 30 in number, are usually from 1 to 5 

 times as long as the diameter of the perithecia. Throughout 

 about half of the length of the appendages they are dark brown 

 in color, and they are also several times dichotomously branched 

 at the tip. A single ascus is given as 58 to 90 by 45 to 75 //., con- 

 taining normally 8 spores. It is believed that the injurious action 

 of this fungus may be easily prevented by the use of copper 

 sprays. 



Podosphaera leucotricha (Ell. and Ev.) Salm. In nurseries of 

 New York and other eastern states this fungus has, during moist 



