SOURCES OF APPLE BITTER-EOT INFECTIONS, 23 



(2) The causal organism survives the Tvinter 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) Mummies. 



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 immime, 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, GlomereUa dngulata may be found in cankers and dead- 

 wood due to various causes. 

 id) 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. 

 (e) 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. 



