72 PROTECTION OF PLA:^jTS, 1920-21 



Conclusions 



1. Dusting has developed very rapidly in the past 8 years. 



2. The results of experimental work in New York, Michigan, Illinois, Nova 

 Scotia and Quebec show dusting to be as efficient as spraying in the control of 

 apple scab and biting insects. 



3. The cost of dusting in the past 2 years has been practically the same as 

 spraying under Qviebec conditions. 



4. The two most important insecticides, calcium arsenate and lead arsen- 

 ate may be safely used with either system. 



5. Without any reliable data to hand it must be stated that dusting is 

 inferior to spraying for the control of sucking insects. However, there is suffi- 

 cient evidence at hand to cause us to believe the solution of this problem will 

 be discovered in the next few years. 



