338 



MANUAL OF FRUIT DISEASES 



was observed several years ago that the Bosc, Sheldon, Seckel, 

 Anjou, Bartlett and others are injured more than the Flemish, 

 Clairgeau and Duchess. The Kieffer, Lawrence and Mount 

 Vernon are relatively resistant to leaf-spot. In the nursery, 

 budded pear-stock, after the first year, may show occasional 

 lesions, but budded stock of two or more years is often badly 

 injured late in the summer. 

 Symptoms. 



Only the leaves are affected. The mature spots are recog- 

 nized by their well-defined angular margins and their grayish 



white centers in 

 which a few pyc- 

 nidia develop (Fig. 

 93). They are 

 found on the upper 

 surface. The for- 

 mation of a spot 

 proceeds as follows. 

 The affected tissue 

 becomes brownish, 

 which discoloration 

 enlarges until the 

 mature size of the 



. Mycosphserella leaf-spot on pear-leaves. .. . g reac h e( l. 



These usually measure about one-sixth of an inch or less in 

 diameter. The margin, while sharply defined, is angular and 

 crenulate. With age the brown color at the center turns 

 grayish white and becomes somewhat transparent. About 

 this light-colored central area is a brown zone which merges 

 into a purplish zone and finally into the healthy green portion 

 of the leaf. Ordinarily lesions are not abundant, but under 

 exceptionally favorable conditions numerous spots develop 

 over the leaf -surf ace. Several may merge, involving large 

 areas of leaf-tissue. 



FIG. 



