PLUM DISEASES 363 



Lodeman, E . G. Black knot of plums and cherries, and methods of treat- 

 ment. Cornell Univ. Agr. Exp. Sta. Bui. 81 : 637-655. 1894. 



Butz, G. C. Black knot on plums. Pennsylvania Agr. Exp Sta 

 Bui. 13 : 3-4. 1890. 



Selby, A. D. Peach yellows, black knot, and San Jose scale. Black- 

 knot. Ohio Agr. Exp. Sta. Bui. 72 : 206-209. 1896. 



LEAF-BLIGHT 

 Caused by Coccomyces Prunophorce Higgins 



Leaf-blight, leaf-spot, shot-hole and yellow-leaf are all names 

 referring to the disease under consideration. A very similar 

 disease affects the cherry (see page 172). 



Among plums the European varieties are notably susceptible 

 to leaf-blight ; these may be completely defoliated in wet sea- 

 sons. On the other hand, Japanese plums and Myrobalan 

 seedlings are comparatively resistant, the disease being of little 

 consequence thereon. 



Affected leaves show dead spots at first (Fig. 105) ; but soon 

 the dead tissue falls away, leaving a circular hole, whence the 

 name shot-hole (Fig. 105). This type of symptom is common 

 on the plum. At times leaves are completely riddled with holes. 

 Sometimes affected leaves turn yellow, whence the name yellow- 

 leaf. The similar disease on cherry shows less shot-holing and 

 more yellowing of the leaves than in the case of plum. In 

 most seasons if sufficient moisture is present, white, velvety 

 pustules appear on the lower surface. These are coils of spores 

 belonging to the conidial form of the causal fungus Coccomyces 

 Prunophorce (commonly known as Cylindrosporium Padi). 



Bordeaux mixture 5-5-50 is effective in the control of plum 

 leaf-blight, but this fungicide may injure the foliage, particularly 

 in nursery-stock. Lime-sulfur, on the contrary, diluted 1-50, 

 may be used without fear of such injury. In the orchard, spray 

 as follows : (1) ten days after the blossoms fall ; (2) three weeks 

 after the first application; (3) three to four weeks after the 



