Diseases and Pests of the Apple and Their Control 237 



crew operating a liquid spray outfit with the old rods. It 

 is estimated that fifteen-year old trees require on the 

 average of about 1 to 1% pounds of dust for a single 

 application, while trees twenty to twenty-five years old 

 require approximately 2 pounds of dust. The time and 

 amount of material vary greatly with the conditions and 

 methods of application. These data will convey in a gen- 

 eral way the relative speed of the two systems. 

 The following formulae are quite generally used : 



Formula' I. Combination dust for chewing insects and 

 fungous diseases: 



Arsenate of lead, powder . . .10 to 15 per cent. 

 Sulfur, superfine 90 to 85 per cent. 



Formula 2. For insect infestations and light fungous 

 attacks : 



Arsenate of lead 10 per cent. 



Sulfur 50 per cent. 



Hydrated lime or gypsum 40 per cent. 



Formula 3. 



Arsenate of lead, powder . .10 to 15 per cent. 

 Hydrated lime or gypsum . . 90 to 85 per cent. 



It is rather difficult to dogmatize on the efficiency of 

 dusting. Some growers, after a more or less thorough trial, 

 are convinced of its economy and efficiency. Other grow- 

 ers have discarded their dusting machines. In western 

 New York dusting has not become general. Improved 

 dusting mixtures and better methods of application may 

 result in greater popularity for this method, for it has 

 certain time-saving advantages. However, at the present 



