ENGLISH: ILLINOIS TREES: THEIR INSECT ENEMIES 



81 



Incomplete spray coverage of a tree may serve to check the 

 ravages of a leaf eater, such as the cankerworm, but control of 

 scale insects or control of the bark beetle that transmits Dutch 

 elm disease requires complete coverage. This is difficult to obtain 

 even with the best of equipment. The tree must be sprayed sys- 

 tematically from many angles and at a time when the wind ve- 

 locity is essentially zero. Careful inspection of a tree or shrub 

 after spraying shows whether proper coverage has been obtained. 



Fig. 58. — Power sprayer in operation. This machine, known as a hy- 

 draulic sprayer, will do an excellent job of spraying trees of small and 

 medium sizes. 



