82 DISEASES OF ECONOMIC PLANTS 



extends for nearly a meter along the branch, and occasion- 

 ally girdles it. When occurring upon the trunk or main 

 branches, body blight is caused, similar in appearance and 

 effects to that mentioned under blight. 



The Tolman Sweet is said to be quite resistant to the 

 canker, while Twenty Ounce is very susceptible. Four 

 other varieties range in susceptibihty as follows : Baldwin, 

 Wagener, Greening, King. 



The Sphaeropsis twig blight somewhat resembles the 

 fire blight with which it is often associated, but may be 

 distinguished from it by the presence of myriads of mi- 

 nute pimples distributed thickly over the affected region. 

 With a hand lens coils of spores may often be clearly seen 

 issuing from these pustules. 



Upon the leaf blighted spots are caused, irregularly cir- 

 cular in outline, often marked by concentric rings. The 

 body of the spot is brownish and the margin sharply lim- 

 ited. Similar spots are caused in several other diseases, 

 and definite knowledge of the nature of leaf spots must 

 depend upon microscopic diagnosis in each special case. 

 Yet it is certain that many of the spots upon apple leaves, 

 especially when Sphaeropsis prevails upon fruit and twigs, 

 are caused by this fungus. 



The various forms of this disease which have been noted 

 in Nebraska, Michigan, Missouri, Ohio, West Virginia, 

 Wisconsin, Kentucky, and Vermont, and throughout the 

 Allegheny and eastern apple sections, are troublesome 

 each year. 



The treatment should be the same as that recommended 

 for bitter rot with special care to avoid bark wovmds of 

 all kinds, as from ladders, workmen's boots, etc. 



