70 PROTECTION' OF PLANTS, 1916-17 



useless because the larvae are down below the surface bark and cannot be 

 reached in this way. The only method that can be safely recommended is 

 to cut out all infested branches and burn them at once, or certainly before 

 May of the following year. Since the trees cannot be saved when they are 

 found to be infested, any precautionary measures which will prevent the de- 

 position of eggs on the trees and the egress of the adult beetles will be found 

 to help very materially. Experiments such as washing the trunks and 

 branches with poisoned whitewash; putting paper wrapping temporarily 

 about the tree; spraying the foliage with Paris green (1 lb. to 100 gals, 

 water) ; painting the bark with a mixture of resin and linseed oil (4 lb. res- 

 in, 1 qrt. oil to 40 gals, water) have been tried. 



All these to a greater or less extent have been helpful but not radical 

 That cure, as has been said, can only come about by the most drastic mea- 

 sures applying the axe or saw. 



Parasites undoubtedly form a very important factor in the natural 

 control of this insect. Birds, such as phoebes, wood-peckers, warblers and 

 chipping sparrows also help, and more effectively too than often given 

 credit for. Their presence in our parks and gardens should be more 

 encouraged. 



If the birches are kept in a healthy condition, free from abnormal 

 growths, loose bark, etc., it will assist them very materially in resisting the 

 attacks of their worst and most destructive enemy, the bronze birch borer. 



