EXPERIMENT STATION BULLETINS. 305 



POWDERY MILDEW OF THE CHERRY (Podosphcera oxycantha (D. C), De By.). 



Like other powdery mildews, this form attacks the leaves and young 

 shoots, often covering them with a fine white powder. It is especially 

 injurious to young cherry trees, but it is also found upon the apple, peach, 

 plum, quince, hawthorn, spiraea, and various other plants of the rose family. 

 It seldom appears before July, and is most injurious in hot, dry summers. 

 The threads of the fungus form a web over the surface of the affected por- 

 tion, and send up great numbers of fruiting stems, which divide into spores. 

 Later on, the winter spores form upon the mycelium and give the fungus a 

 grayish appearance. Under the microscope the black spores cases are seen 

 to be flattened on one side, and to have long appendages, which bear at 

 their extremities curiously branching tips (Fig. 29, 7). Occurring as it does 

 late in the season, after the growth has been nearly completed, it seldom 

 does much harm but, as it undoubtedly weakens the growth, measures should 

 be taken to keep it in subjection. In most cases, the treatment recommended 

 for brown rot and shot-hole fungus will suffice to hold it in check. 

 It some cases it may be necessary to spray the trees for this disease later 

 in the season than will be necessary for the others. 



SHOT-HOLE FUNGUS {Cylindrosporium padi, Karst). 



This and other closely allied fungi often do great injury to the differ- 

 ent species of the cherry. It appears as small, purplish spots upon the 

 leaves. These soon turn yellow and finally brown, and then drop out, 

 leaving small round holes resembling those made by shot. Oftentimes a 

 large number of holes appear in a leaf, and as a result nearly all of the 

 foliage drops from the trees. In this condition the trees are unable to 

 ripen their wood, and, as a result of their unripened condition, are 

 killed, even in a mild winter. It seldom appears until midsummer, but if 

 the season is hot and dry, and particularly if the trees are neglected and 

 uncultivated, it often causes large losses. If a little attention is given 

 to spraying for this disease, after the fruit is gathered, using Bordeaux 

 mixture once or twice, it will do little if any harm. 



OTHER DISEASES OF THE CHERRY. 



The cherry has a number of other diseases, most of which will be found 

 described under other fruits; among them are black knot (Plowrightia 

 morhosa), the scab {Cladosporium carpophilum) , and rust {Puccinia 

 pruni). 



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