INSECT PESTS OF OHIO SHADE AND FOREST TREES 171 



large trees are all mixed together, the one sort may be best sprayed 

 with one type of nozzle or apparatus while the other may require 

 an entirely different kind, and the time involved in the changing 

 is both laborious and expensive. 



Plant to make insect warfare possible. — Tall growing species 

 subject to insect attack should not be planted in situations where 

 the application of insect control measures is rendered difficult or 

 impossible. For example, when trees are planted too close to build- 

 ings it is almost impossible to spray them properly without some of 

 the mixture soiling the building. Those who have had experience 

 will recall wdth regret the proceedings which usually follow after 

 inadvertently covering the walls or windows of a house, especially 

 if the work is being directed by public officials. The offense is 

 sufficiently serious if a material is being used which readily washes 

 off and leaves no permanent bad results ; but it takes on the aspect 

 of the unpardonable if the sulphur sprays, so frequently employed 

 for scale control, are used, as these materials combine chemically 

 with the paint of the walls, leaving them disfigured by ugly dark 

 spatters and blotches. 



CONTRIBUTING CAUSES TO DECREASED VITALITY OF TREES 



Street trees require protection from mechanical injuries. — The 



chance for the city tree, particularly the one planted on the street, 

 to receive mechanical injury is so great that means should be pro- 

 vided for its protection, especially during the earlier years of its 

 life. The bark on the trunk and limbs of the young tree is very 

 tender and when broken affords an excellent opportunity for the 

 establishment of insect pests and fungous diseases. Such abrasions 

 offer ideal entrance points for many of the boring insects. 



These mechanical injuries may arise from several sources, the 

 three most important of which are the biting of horses, thoughtless 

 mutilation by passersby, and injuries by building operations and 

 linemen. 



Biting by horses. — With the increasing abundance of delivery 

 automobiles and the corresponding decrease in the numbers of 

 untied delivery horses, this menace to tree growth is rapidly 

 becoming eliminated, but still remains a point of sufficient import 

 to occupy our attention. After a wound is once started it is fre- 

 quently kept open by having the healing edges gnawed until ulti- 

 mately it may become a large, cankerous .spot, not only unsightly 

 and weakening to the tree but affording an ideal point of attack for 

 boring insect pests. (See Plate III, Fig. 1.) Trees standing 



