86 MANUAL OF FRUIT DISEASES 



to three years old are sources of trouble. Furthermore, diseased 

 bark which falls to the ground may develop the ascospores as 

 described above. And finally, the inocula (conidia and asco- 

 spores) may come not only from the apple-tree but from the 

 pear, on which fruit-tree the fungus also occurs. 



Control. 



In applying remedial measures it should be borne in mind 

 that: (1) while the disease appears to be most serious on 

 certain varieties, no variety is wholly immune ; (2) the disease 

 is caused by a fungus ; (3) the causal fungus infects the trees 

 in the fall, particularly from October to December; (4) the 

 fungus can enter through wounds, lenticels or unbroken sur- 

 faces ; (5) cankers produced on the limbs are the only source 

 of the inocula these give rise to all the trouble ; (6) these 

 cankers are a dangerous source even when three years old ; 

 (7) fallen bark from one-year-old cankers is also a source of the 

 inoculum ; (8) the fungus inhabits not only the apple, but also 

 the pear, which may be a source of trouble. 



It is therefore out of the question at present to rely on any 

 variety to resist the attacks of the fungus. Any spraying 

 which is done must be accomplished before the most important 

 period of inoculation and infection. It has been shown that 

 old orchards may be cleaned by proper spraying. Bordeaux 

 mixture 6-6-50 is said to be better than lime-sulfur for this 

 purpose. For this disease spray as follows: (1) as soon as 

 possible after the fruit is picked ; (2) again within two or three 

 weeks. Where the trouble is serious an application should be 

 made at least once before the fruit is picked ; this may be made 

 about September 15, or before the first autumn rains. Then 

 spray twice as directed above. These applications should 

 thoroughly coat the limbs to protect them from the attacks of 

 the fungus. Cankers on the more valuable limbs of younger 

 trees may be removed, in which case the debris should be 

 destroyed and the wound coated with coal-tar. The removal 



