14 FRUIT TREES AND THEIR ENEMIES 



the proportions taken when making an insecticide ; 

 but unless the alteration is based on actual knowledge 

 or experience, it is well not to attempt it ; for too often 

 such alterations may result either in injury to the 

 trees, or in the failure of the spraying to effect its 

 purpose. Still more should growers not attempt to 

 mix various insecticides together, unless they are 

 thorough masters of the chemistry of the substances 

 concerned. Such haphazard mixing will generally 

 result in the destruction of the valuable properties of 

 one or all of the substances in question. 



Above all, it should be remembered that it is mere 

 waste of money to spray, unless the spraying is done 

 thoroughly. One thorough spraying may succeed in 

 destroying a pest, where several slipshod sprayings 

 will have no permanent effect whatever. Every 

 portion of the tree should be thoroughly wetted. If 

 heavy rain falls soon after trees have been sprayed, 

 the work may have to be done over again ; but a 

 certain amount of rain is often beneficial, as it prevents 

 the wash from drying up too quickly, and helps to 

 distribute the liquid over parts which might otherwise 

 not have been wetted by it. 



Spraying, it should be remembered, is rather a cura- 

 tive than a preventive measure. There is no good in 

 spraying a tree if there is nothing on it to be destroyed ; 

 indeed, there may be positive harm in doing so ; for, 

 though spraying, when required, results indirectly in 

 improving the trees and the crops, by destroying pests 

 attacking them, yet the substances used may of 

 themselves be injurious to the plant, and the continual 

 use of them often causes damage. Spraying a healthy 



