10 BULLETIN 534, U. S. DEPARTMENT OF AGRICULTURE. 
This orchard, consisting of trees of Missouri, a very susceptible 
variety, was, prior to 1913, badly infected with blotch. In fact, pre- 
vious to 1913 the orchard, mainly because of blotch, had not matured 
a crop. After three years of thorough spraying, done at the proper 
time, the trees are almost free from twig cankers and the disease 
is nearly eliminated from the orchard. 
Spraying, then, not only prevents the infection of fruits during the 
current year, but tends also to lessen the number of possible infec- 
tions during succeeding years. Furthermore, since, as the writer (4) 
has shown, the bitter-rot fungus may live through the winter in blotch 
cankers, the elimination of the latter may be an aid in the control of 
bitter-rot in orchards in which that disease is present. 
SUMMARY. 
(1) Apple blotch, a serious disease of the more southern apple- 
growing sections of the United States, affects the twigs, fruit, and 
leaves of the apple. It has been shown by previous investigators 
(Waite, Clinton, Sheldon, and Scott and Rorer) to be caused by the 
fungus Phyllosticta solitaria, which, as Sheldon and Scott and Rorer 
discovered, winters over in twig cankers and infects the young fruit, 
leaves, and twigs during the following year. Neither Scott and Rorer 
nor Lewis considered mummied fruit of the previous year an impor- 
tant source of infection. 
(2) The writer has made successful cross inoculations on fruit, 
leaves, and twigs from pure cultures of the fungus obtained from 
naturally diseased fruit and twigs, thus confirming the inoculation 
work of Scott and Rorer, which, however, was not done by the use of 
pure cultures. 
The reason so few infections occur late in the season is due to the 
increased resistance of the host, in addition to the fact that there is a 
gradual decrease in the number of spores produced by the causal 
fungus. A large number of mummied fruits were examined at in- 
tervals throughout the spring, but no spores were found. Hence 
it is concluded that mummies are not an important source of infection. 
Wet weather favors blotch, but in orchards in which twig cankers 
are abundant the disease is not checked effectively by dry weather. 
(3) The disease is controlled by three sprayings with 38—-4-50 
Bordeaux mixture at intervals of three weeks, the first of which 
should be completed about three weeks after the blossom petals have 
fallen. Summer-strength lme-sulphur solution may be substituted 
for Bordeaux mixture where the disease is not severe, thus lessening 
the risk of injury. The proper time for the first application has been 
determined both by spraying experiments and by spore germination 
tests in the laboratory. This spraying schedule differs only shghtly 
from that originally worked out by Scott and Rorer. 
