130 MANUAL OF FRUIT DISEASES 



Morse, W. J. Spraying experiments and apple diseases in 1913. 

 The European apple canker in Maine. Maine Agr. Exp. Sta. Bui. 

 223 : 23-24. 1914. 



SUPERFICIAL BARK-CANKER 

 Caused by Myxosporium corticolum Edgerton 



In certain of the northeastern states apples and pears are 

 affected with a superficial bark-canker. In practically every 

 apple or pear orchard of New York and neighboring states there 

 is more or less of this disease. But even in those orchards where 

 every tree is affected there is no evidence that serious damage is 

 being done. Every branch of a tree may be extensively affected, 

 while large, bearing limbs commonly exhibit cankers of consid- 

 erable extent, but in spite of these facts the disease is probably 

 never injurious. Its superficial nature accounts for this in a 

 satisfactory manner. 



Symptoms. 



The common occurrence of this disease is sufficient in itself to 

 warrant a description. Many growers and even scientists have 

 confused the superficial bark-canker with the black-rot canker. 

 The former disease, like the latter, is found chiefly on the older 

 and larger limbs. But there is no striking depression developed 

 in the case of the superficial canker as with the black-rot canker. 

 At most there is but a slight sinking of the affected bark. The 

 outer bark is killed, and a sharp crevice marks the extent of the 

 lesion (Fig. 34). This line of demarcation is prominent and 

 takes an irregular course on the affected limb. The originally 

 infected areas are small and more or less circular, but large 

 cankers of various shapes finally appear as a result of the coales- 

 cence of two or more cankers. Accompanying the pathological 

 changes in the normal bark minute pustules develop in the 

 affected area; these dot the surface and resemble very much 

 those on the black-rot canker. (Compare Figs. 13 and 34.) If 



