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 

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

 a peculiar light green color which gradually changes to dark 

 brown or black as tlie tissues die. In many cases tlie leaves wrinkle 

 in a peculiar manner, due to the growth of the surface being re- 

 tarded irregularly. The scab passes the winter upon the old leaves 

 in the orchard and the pores reinfest the trees the folloAving spring 

 from these old leaves ; the first infections usually coming on the 

 lower side of the leaves. 



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

 but can be cuiitioUed by thorough spraying. 



^Susceptibility to Seal). — 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 

 or twice thereafter at intervals of two to four weeks. The rela- 

 tive importance of these sprayings will vary with the season. If 



