512 BULLETIN 333 



JUDICIOUS PLANTING AS AN AID IN THE CONTROL OF 



THESE PESTS 



In view of the wide and serious injury to shade trees by many different 

 insects, it becomes pertinent to discuss some general principles of control 

 of such pests. In the first place, it is unwise to depend almost entirely 

 on one species of tree for shade or ornament. The very existence of 

 the American elm, for example, in the eastern United States at least, 

 is threatened by two serious pests, the elm leaf -beetle and the leopard 

 moth. Probably the elm leaf -beetle could be controlled if every owner 

 of elm trees would spray. It is quite probable that the leopard moth 

 cannot be controlled and that eventually the elms will succumb to these 

 two pests. The trees have already disappeared from the Harvard Yard 

 as a result of the ravages of these insects. The sugar maples are becoming 

 more and more subject to serious injuries from borers. Many fine trees 

 are dying each year and there seems to be no help for the situation. 

 The graceful white birches are going one by one as a result of the ravages 

 of the bronze birch borer, while the hickories are hard beset by the hickory 

 bark-borer. 



With these facts in mind, it is important to give careful and thoughtful 

 consideration of the question of the wise selection and planting of shade 

 trees. A city in which the streets are planted only to elms and maples is 

 likely to be without shade trees in the near future. The wide planting 

 of one kind of tree over considerable territory forms ideal conditions 

 for the increase and spread of an extended outbreak of an injurious 

 species of insect. On the other hand, if adjacent streets are planted to 

 different varieties of shade trees an outbreak of any single pest can be 

 checked and controlled much more easily. Elms and maples can well 

 be supplanted in many cases by oaks, especially the pin oak and the red 

 oak, or by the ginkgo tree a handsome but rather slow-growing tree, 

 and one remarkably free from pests. The Norway maples make fine 

 shade trees, and so do the linden, the horse-chestnut, and the American 

 ash. 



