f 
SOURCES OF APPLE BITTER-ROT INFECTIONS. 93 
(2) The causal organism survives the winter in certain parts of 
the host, which serve as sources of the infections occurring on the 
crop of the following year. It may survive in— 
(a) 
(6 
— 
(¢) 
(ad) 
(e) 
(f) 
Mummies. eh 
Clinton, Hasselbring, Burrill and Blair, Alwood, Von Schrenk and 
Spaulding, Scott, and the writer showed mummies to be important 
sources of infection. 
Apparently the fungus lives over in a mummy for only one year. 
Both those mummies on the tree and those on the ground are important. 
Bitter-rot cankers, 
The cankers were discovered by Simpson in 1902. 
Von Schrenk and Spaulding proved them to be caused by the bitter-rot 
organism. 
Cankers on young vigorous-growing branches do not survive till the 
next season. Those on older twigs, especially of very susceptible 
varieties, may survive for years. Different varieties show different 
degrees of susceptibility to the cankers. Certain ones, such as the 
Yellow Newtown and York Imperial, are nearly immune, though 
their fruit, especially that of the Yellow Newtown, is susceptible to 
the disease. 
Cankers other than those of bitter-rot. 
Especially in western orchards, in which the disease has been particu- 
larly severe, Glomerella cingulata may be found in cankers and dead- 
wood due to various causes. 
Leaves. 
As first shown by Shear, the fruits of the causal organism may some- 
times be found on leaves of the current year when removed and 
subjected to moist, hot conditions. The writer, however, has never 
been able to isolate the fungus from leaves of the previous season. 
Other host plants. 
The fungus is able to infect many plants other than the apple. 
Infected fruits of the current year. 
By conidia produced in these secondary sources of infection the dis- 
ease is carried to sound fruits. This is the principal means by which 
the disease is spread after the initial infection. 
(3) Spore dissemination is comparatively restricted and is carried 
on through the agency of rain, dew, insects, and possibly birds. 
Wind is a negligible factor. 
(4) Varieties differ greatly as to susceptibility to the disease. 
Hot, moist weather favors infection. 
(5) The removal of mummies and cankers is a practicable and 
efficient control measure when supplemented by spraying. This 
treatment gave control in orchards in which in previous years spray- 
ing alone had been uniformly unsuccessful. 
