20 MANUAL OF FRUIT DISEASES 
The history of bitter-rot shows that it has always been spas- 
modic and erratic in its occurrence in different seasons. But 
the irregularity is not confined alone to different seasons, for it 
makes its appearance in different years at different dates. In 
different orchards it may occur at widely separated intervals 
during the same season. The fruits on the sunny side of a tree 
frequently are destroyed first. Sometimes the crop on the 
south side of a tree is destroyed while on the north side it es- 
capes the disease. Likewise the fruit on the inside, lower 
branches, being well protected from the sun, often escapes, 
whereas apples exposed to the sun are ruined. Trees in the 
shaded mountain hollows of Virginia are said to show less rot 
than trees in situations more exposed to the sun. 
All of these points indicate a decidedly close relationship 
between the fungus and the weather, especially temperature. 
The fact that the fungus is confined to the warmer states, that 
it appears chiefly in July and August, and that fruits exposed 
to the sun are destroyed first, point unmistakably to the fact 
that the pathogene is a hot weather fungus. Furthermore 
cold weather usually checks the disease —or may stop it 
altogether. A cold spring may retard the development of the 
fungus at that season, but there usually results a later attack 
on the fruit. In cool, dry summers bitter-rot is sparingly 
present. Conditions most favorable for the development of 
the disease are warm, moist weather. A short series of hot, 
wet days in August may bring about a sudden and very 
destructive attack. Nights with a heavy dew, alternating 
with hot days, are usually followed by an extensive outbreak 
of the disease, even destroying the whole crop in three days. 
Control of bttter-rot. 
Cankers, being a chief source of the inoculum, should be re- 
moved. Remove the whole limb except where the affected 
branch is a large and valuable one. Dead parts and cankers 
other than bitter-rot lesions should be removed. All these 
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