416 



BULLETIN 371 



of the perithecia are thus destroyed and the source of early infections 

 is to a considerable extent eliminated. On the other hand, this treatment 

 is not sufficient to completely control the disease, for usually enough 

 old leaves remain scattered about to enable the fungus to gain a foot- 

 hold on the new leaves. 



In order to forestall these attacks of the fungus and subsequent in- 

 fections by spores from the pycnidia, the leaf surface must be covered 

 with a fungicide that is poisonous to the parasite. When the spore 

 germinates, the germ tube comes in contact with the fungicide and is 



FlG. 89. A POWER DUSTING OUTFIT 



This machine is suitable for dusting large trees 



killed, and thus its entrance into the tissues of the leaf is prevented. 

 The fungicide does not penetrate the leaf and kill the mycelium, 

 and since the spores are very minute- being about y*W of an inch in 

 diameter the fungicide must be applied so that it completely covers 

 all parts of the leaves. The applications must be made at such intervals 

 as will afford the greatest amount of protection throughout the summer. 

 The proper time for the first application, especially for nursery stock, 

 is soon after the buds open in the spring. This should be followed by 

 at least two other treatments, made at intervals of from two to three 

 weeks. In rainy seasons it is advisable in many cases to make one or 



