166 DISEASES OF FRUIT TREES 



produces very characteristic spots which are a peculiar olive 

 green in the early stages but soon become blackened, the skin 

 usually breaking about the margins of the spot. In very bad 

 cases the spots coalesce and the fruit may crack open nearly to 

 the core (see Fig. 90). On the leaves the spots are usually 

 nearly circular in outline, at least in the beginning, and are of 

 a peculiar light green color which gradually changes to brown 

 as the tissues die. In many cases the leaves wrinkle in a peculiar 

 manner, due to the growth of the surface being retarded irregu- 

 larly. The scab passes the winter upon the old leaves in the 

 orchard and the spores reinfest the trees the following spring 

 from these old leaves. 



Fia. 71. — Scab, or black-spot of the apple. This is the most serious of all the apple diseases, 

 but can be controlled by thorough spraying. 



Susceptibility to Scab. — There is a very marked difference in 

 the relative susceptibility of different varieties of both pears and 

 apples. Among pears the Flemish Beauty is peculiarly liable 

 to attack and the crop is frequently ruined, many specimens 

 being cracked nearly to the core, while adjoining trees of 

 Bartlett may be relatively little affected. "With apples the 

 Fameuse, Rhode Island Greening, Mcintosh and Spy are among 

 those which are especially subject to attack. 



The treatment for scab, in either pears or apples, consists 

 in spraying with lime-sulfur or Bordeaux mixture, and the 

 number of applications varies with the locality, the season and 

 the variety. If a bad attack is expected the trees should be 

 sprayed before the blossoms open, just after they fall and once 



