30 INSECT AND FUNGOUS ENEMIES OF THE APPLE. 
gradually enlarges, finally attaining a size of one-fourth or some- 
times one-half inch in diameter. (See fig. 16.) The advancing mar- 
gin usually has a fringed appearance, and the surface is dotted with 
minute, black, raised dots known as pyenidia. 
The spots may become so numerous as practically to cover one side 
of the apple, causing it to ripen and drop prematurely. They are 
usually accompanied by a cracking of the fruit, thus opening the way 
for other fungi and insects as well. Some of these cracks are very 
small, while others are half an inch or more in length. The appear- 
ance of affected fruit is so marred as to render it practically unfit for 
market. 
On the twigs.—The fungus causing apple blotch attacks the twigs, 
fruit spurs, and “ water sprouts,” producing small brown cankers 
with purplish margins. These 
cankers are usually only about 
one-fourth by one-half inch in 
size, but may become consider- 
ably larger and often girdle 
the affected twig. With age 
the bark over the diseased area 
becomes cracked and scales up, 
giving the canker a rough ap- 
pearance. These cankers as a 
rule do no serious damage to the 
tree, but the fungus passes the 
Fic. 16.—Maiden Blush apple affected with winter in them and they thus 
apple bloteh. become a dangerous source of 
infection for the new fruit crop. 
On the leaves—The leaves also become affected and here the disease 
manifests itself in the form of very small light-brown or yellowish 
spots. These spots are angular in outline and attain a size of only 
about one-sixteenth of an inch in diameter. The spots are usually 
very numerous on leaves of trees affected with the twig cankers, but 
they are so small that the injury produced is not often serious. 
CAUSE OF THE DISEASE. 
Apple blotch is caused by the fungus Phyllosticta solitaria EB. & FE. 
The fungus lives over winter in the twig cankers, where it is perennial, 
and in the spring produces spores which ooze out in great numbers 
from little black raised points or pycnidia. These spores are carried 
to the fruit by rains, wind, and perhaps insects. Upon germination 
in the presence of moisture they throw out one or two fungous threads, 
which penetrate the skin, become much branched, and grow slowly in 
a radial manner, finally producing the brown blotches. 
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