Tree Growing 97 



It may not be out of place to repeat that the danger from 

 this source is much lessened if too many of the same species 

 are not planted together. For purposes of treatment, in- 

 sects may be divided into two groups, those that injure 

 trees by eating the foliage and those that pierce the outer 

 skin of the leaf and suck the juices. The eating insects 

 include the larvae of a great many moths, butterflies, flies 

 and beetles, but they may all be treated in the same way. 

 Insects are very susceptible to arsenic poisons, of which 

 the best known is Paris Green. Difficulty in procuring 

 Paris Green has made it advisable to substitute arsenate 

 of lead which is easily obtainable on the market now, either 

 in the form of a powder or as a paste. 



The sucking insects include the green aphis or plant 

 louse, the woolly aphis and all kinds of scale insects. 

 These names do not apply to single species but to types, 

 each type including a large number of species. They must 

 be treated with a spray which kills by contact, and the 

 best, or at least cheapest, is made by forming an emulsion 

 of coal oil and soap. The following extract from the re- 

 port of Mr. J. M. Swaine of the Entomological Branch of 

 the Department of Agriculture, Ottawa, gives very clear 

 instructions for thfe making and use of the sprays. 



"Lead Arsenate. Leaf -feeding insects of all kinds are usually 

 best controlled by poison sprays. Lead arsenate is one of the 

 best of these for use on shade-trees ; its initial cost is somewhat 

 higher, but it adheres to the foliage longer, and does not often 

 burn the leaves when used at the ordinary strength. It is 

 usually sold in the form of a paste, and should be worked up 



