28 INSECT AND FUNGOUS ENEMIES OF THE APPLE. 
months in which such temperatures usually occur. Infections may 
begin to take place during the latter part of June if the weather con- 
ditions are right, but since the fungus does not thrive on young, green 
fruits, no serious outbreak need be feared until July. Owing to cli- 
matic influence the bitter-rot disease is confined mainly to the south- 
ern tier of apple-growing States. 
The second limiting factor, namely, varietal resistance, varies in 
different sections of the country. For example, the Yellow Newtown 
in Virginia is very susceptible to the disease, and under favorable 
conditions the entire crop may be destroyed, while the Ben Davis in 
the same orchard will become only slightly, or not at all, affected. 
On the other hand, the Ben Davis, in portions of the Middle West— 
southern Illinois, southern Missouri, and northwestern Arkansas—is 
one of the most susceptible varieties. This would indicate that there 
are two strains of the fungus, the Ben Davis being susceptible to the 
one occurring in the West and resistant to the one occurring in 
Virginia. 
The most susceptible varieties grown in bitter-rot sections are 
Yellow Newtown, Willow, Huntsman, Smokehouse, Stark, Jonathan, 
Ben Davis, and many other less prominent varieties. 
TREATMENT. 
Although it has been abundantly demonstrated that bitter rot can 
be readily controlled, even under the most severe conditions, many 
apple growers look upon it as the most treacherous of all the diseases 
with which they have to contend. The chief reason for this is the 
irregularity with which the disease appears. One year an outbreak 
may occur in July, while the next year the disease may not appear 
until September. Varieties partly resistant to the disease may go 
through several seasons without becoming affected, but when there 
comes a season unusually favorable to the fungus, much of the fruit 
of these varieties may be destroyed by the disease. This erratic habit 
of the disease keeps the apple grower in doubt as to when to expect it 
and when to spray. He does not care to give his orchard three or 
four bitter-rot sprayings when there is no bitter rot to fight, and he 
is loath to begin the treatment in June if the disease does not occur 
until September, yet the only safe plan in bitter-rot districts is to ex- 
pect the disease every year and to keep the fruit protected from the 
latter part of June until the end of September. 
Bordeanx mixture is still the best fungicide to use for bitter rot, 
the lime-sulphur solution having proved only partially effective 
against this disease. Fortunately Bordeaux mixture has very little 
or no injurious effect on the apple after the young fruits have at- 
tained an age of 6 or 8 weeks, and may therefore be used for bitter 
rot with comparative safety. 
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