198 



THE NURSERY-MANUAL 



certain degree, in controlling apple mildew, but the addition 

 of 3 pounds of iron sulfate makes a more effective mixture. 

 Dusting with a mixture of 90 parts sulfur and 10 parts powdered 

 arsenate of lead also has proved satisfactory in checking the 

 mildew. 



In some seasons the mildew is more prevalent than in other 

 years, and when the disease is abundant an effort should be 

 made to keep as much as possible of the new 

 growth covered with the fungicide. The first 

 application should be made soon after the seed- 

 lings have developed the first new leaves. 

 Three or four subsequent treatments should be 

 made at intervals of two to three weeks. 



YELLOW-LEAF DISEASE OF CHERRY AND PLUM. 

 - The yellow-leaf may be very destructive to 

 nursery trees when weather conditions are 

 FIG. 213. Yel- favorable. Mazzard cherry seedlings are ex- 

 low-leaf disease of ceedingly susceptible and often badly defoli- 



cherry. . & J i i r i ir 



ated. Mahaleb cherry seedlings are commonly 

 affected, while myrobalan plum seedlings show a considerable 

 degree of resistance. The sweet and sour varieties of cherry 

 and the European varieties of plum are more susceptible to the 

 disease than the Japanese plum varieties. 



Description. The disease appears on the cherry foliage as 

 dark red spots, that may be abundant on the leaves (Fig. 213). 

 In the advanced stages of the disease, a yellowing of the affected 

 foliage may occur and the leaves fall prematurely. On the 

 plum foliage the disease is conspicuous because of the shot- 

 hole appearance of the leaves caused by the dropping out of 

 the circular areas of affected tissue. The same yellowing 

 sometimes appears on diseased plum leaves but never so abun- 

 dantly as on sweet cherry foliage. 



Cause. The yellow-leaf disease on cherry is caused by the 



