24 INSECT AND FUNGOUS ENEMIES OF THE APPLE. 
CHARACTER OF THE INJURY. 
The fungus causing apple scab attacks the fruit, foliage, and to a 
much less extent the twig. The greatest damage is done to the fruit, 
on which it produces the scabby spots familiar to most apple 
growers. These spots are circular, though somewhat irregular, in out- 
line, dark gray or olivaceous in color, becoming blackish with age, 
and they range in size from mere specks to spots one-fourth inch or 
sometimes one-half inch in diameter. (See fig. 13.) The fungus 
ruptures the epidermis of the apple, forming a gray, jagged ring at 
the border of the healthy tissues. Two or more spots may coalesce, 
forming a large scabby area, in some cases covering one side of the 
apple. The disease prevents the normal development of the fruit, 
the affected side becoming dwarfed, pitted, and otherwise deformed. 
It also causes the development of cracks, which may extend half 
Fic. 13.—Apples affected with the scab fungus, the one on the left showing characteristic 
spots and the one on the right smaller spots with crack. 
way around the apple and almost to the core. <A large percentage of 
the affected fruit drops to the ground before maturing. 
~ Ina cool, wet spring the blossom buds and young fruits in blossom 
may be attacked and destroyed. Occasionally, though rarely, the 
entire crop of an important fruit section may be destroyed in this 
manner. 
The disease occurs on both sides of the leaves, forming smoke- 
brown or olivaceous patches which become swollen and _blisterlike. 
(See fig. 14.) The affected leaves often curl somewhat and may 
drop prematurely. The fungus is said to occur also on the twigs, 
forming blackish-olive patches, but this is apparently not common in 
the United States. 
THE FUNGUS CAUSING THE DISEASE. 
Apple scab is caused by a fungus known as Venturia pomi (Fr.) 
Wint., which lives over winter in the fallen apple leaves. In the 
spring, when the weather becomes warm enough to start apple trees 
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