PEAR DISEASES 335 



ment. However, much of the food for the fungus no doubt 

 comes from the attacked cuticle. 



Infection of the various parts continues throughout the grow- 

 ing season. In the fall the affected leaves drop to the ground, 

 carrying the fungus with them. Soon the mycelium changes its 

 superficial habit and permeates the entire leaf. Before cold 

 weather, perithecia begin their development within the old 

 dead leaf-tissues. These bodies remain immature until spring, 

 when they resume growth. This begins at least by the time 

 the pear-tree starts into growth. By the time the blossom- 

 buds are showing white the perithecia contain mature asco- 

 spores which are discharged during periods of moisture. Their 

 ejection is accomplished with force enough to carry them into 

 the air, where they are easily caught .by the wind and are blown 

 to the opening buds. The germination of these spores finally 

 results in infection. The period over which ascospores are dis- 

 charged is not definitely known, but reasoning from the known 

 facts concerning the apple-scab fungus the period probably 

 extends over several days. 



The pear-scab fungus also passes the winter on the twigs. 

 The mycelium and conidia remain alive from autumn until 

 spring, when new infections are initiated. Twigs are commonly 

 affected, so that this method of hibernation is unquestionably of 

 considerable importance. It is not known nor believed to be 

 true that the fungus winters over on fallen fruit. 



Control. 



Pear-scab, although found everywhere, can be controlled 

 effectively. That it is not held in check in many orchards where 

 spraying for it is done is no indication that it cannot be 

 prevented. Time and thoroughness of the applications of 

 fungicides are of prime importance. 



The number of sprayings will depend somewhat on the his- 

 tory of the management of the orchard in the past. If the 

 orchard has been well sprayed, three applications will suffice 



