18 



ILLINOIS NATURAL HISTORY SURVEY 



CIRCULAR 53 



Fig. 16.— Elms killed 

 with potassium iodide, as 

 shown by the tree at left 

 which has lost its bark, 

 will not be colonized by 

 bark beetles. 



Fig. 17. — An ax frill, in which 

 potassium iodide is introduced 

 into a tree, is made by chopping 

 a continuous angling cut around 

 the trunk. 



Foliar spray. To obtain maximum protection of special value 

 elms, a foliar spray can be applied after second growth of leaves 

 occurs, usually in late July in Illinois. This foliar spray is half the 

 strength of the dormant spray described in the "Spraying" section. 

 It is not recommended for a communitywide control program. 



