INFLUENCING CONDITIONS. kS 
weather may start an epidemic that will destroy the entire crop of 
certain varieties, provided the fungus is present. 
Moisture.—Moisture is not only necessary for the germination of 
the spores, but it favors the growth of the fungus and hastens spore 
production. In a moist atmosphere the spores are produced much 
more rapidly than when the air is ary. Moreover, rain is an active 
agent in the spread of the disease, splashing the spores from an 
affected apple to adjacent healthy fruits. Heavy dews followed by 
hot cloudy days with a humid atmosphere appear to make ideal con- 
ditions for the rapid development of this disease. 
Temperature.—The fungus causing this disease is decidedly a hot- 
weather fungus and rarely is a serious pest north of latitude 40° N. 
July, August, and September are the three bitter-rot months, and a 
maximum temperature near 90° F. for several days in succession, 
coupled with suitable moisture conditions, is necessary to start a 
serious outbreak. Infection of some fruits may take place as early 
as the middle of June,” but the fungus grows slowly and fruits spar- 
ingly until the warmer weather of July increases its rate of develop- 
ment. In Virginia, on July 10, 1905, the writer observed bitter-rot 
spots covering a quarter to half of the apple. One specimen was 
somewhat more than half involved in rot, and the numerous rings of 
spore masses indicated that the fungus had been fruiting abundantly 
for days, and the infection had doubtless taken place a couple of weeks 
earlier. The variety was Yellow Newtown, and the fruit was scarcely 
more than half grown. The proper combination of heat, moisture, 
and an abundance of spores may not occur until August or September, 
or in some seasons not at all. 
The fungus is so influenced by the heat of the sun, and perhaps by 
the light aiso, that the fruit on the south side of a tree may become 
badly affected before the disease is noticeable on the opposite side. 
Stinson? observed this fact, and in the Virginia orchards the writer 
found that almost invariably the fruit on the sunny side was destroyed 
first, and oftentimes a portion of the crop on the north side would 
escape when the destruction was complete on the south side. This 
held true not only in the particular orchard under experimentation, 
but in many orchards visited during the outbreak of 1903, and during 
the past season as well. Moreover, it was observed that fruit on the 
inside lower branches well protected from the sun was less attacked 
and often escaped when that on exposed portions of the same tree was 
destroyed. Owing perhaps to exposure to the sun there was a con- 
siderably higher percentage of rotten fruit on trees partly defoliated 
with leaf-spot fungi than in the case of trees with full foliage. Not 
only is the fruit on the sunny side of the tree worse affected, but the 
@See Burrill.and Blair, Bul. 77, Ill. Agr. Exp. Sta., p. 332. 
6 Bul. 1, Missouri State Fruit Experiment Station, p. 6. 
