. Dutch elm disease in Illinois . 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.

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