12 THE CONTROL OF APPLE BITTER-ROT. 
fungus is spread from tree to tree and from orchard to orchard. It 
seems, however, that the mummied fruit and the limb cankers are both 
instrumental in carrying the fungus over winter and starting the 
annual infection, and that insects play an important role in the spread 
of the spores. : 
During the season of 1903 and again in 1905 the writer visited a 
number of infected orchards in Virginia and West Virginia, making 
special observations upon this problem. The results lead to the con- 
clusion that the overwintering mummies hanging on the trees consti- 
tute the chief source of infection, at least in this particular region. In 
the majority of cases examined a mummy could be found in the upper 
portion of the infected area, but in no case was there found associated 
with such outbreaks any cankers that could be identified as bitter-rot 
cankers. However, from observations made in the Middle West, Bur- 
rill and Blair® and von Schrenk and Spaulding’ conclude that the 
canker is the chief source of early infection, the fungus being held over 
winter in the diseased limbs and producing spores for the infection of 
the new crop of apples. Hasselbring*’ demonstrated that the fungus 
of bitter-rot remains alive over winter in the mummied apples. It 
seems possible that the mature spore form of the fungus discovered 
by Clinton may develop the following spring in the mummied fruits, 
starting the infection on the new crop. 
After one apple on a tree becomes diseased and begins to produce 
spores, further infections may readily take place through the medium 
of raindreps which splash the spores to adjacent fruits, and heavy 
dews may wash the spores to the apples below. Insects are also 
undoubtedly instrumental in disseminating the disease,” and they are 
possibly the chief carriers of the spores from tree to tree. On the 
other hand the rapidity with which the disease frequently spreads over 
an orchard, practically destroying the entire crop within a few days, 
suggests the idea that the spores are carried on the wind, and indeed 
they seem to be omiipresent in the bitter-rot districts, only awaiting 
suitable weather conditions. But the spore masses being sticky when 
wet and glued to the skin of the apple when dry, there seems to be 
little or no chance for the wind to carry the spores. 
INFLUENCING CONDITIONS. 
WEATHER. 
The predominating conditions that influence the development of 
pitter-rot are temperature and humidity. A few days of hot showery 
@ Bul. 77, lll. Agr. Exp. Sta., p. 356. 1902. 
> Bul. 44, Bureau of Plant Industry, U. S. Department of Agriculture, 1903, pp. 
36-38. 
¢ Burrill and Blair, |. c., p. 354. 
@ Clinton, G. C., Bul. 69, Ill. Agr. Exp. Sta., p. 197. 
