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Summer Defoliators

Yellow-necked caterpillars, walnut caterpillars, and late first-generation mimosa webworm are still causing damage in southern Illinois and in select locations in central Illinois. Where defoliation is extremely severe or where plant appearance is the most important aspect of the landscape, treatments with any of the compounds listed for caterpillar control in the 1997 Illinois Commercial Landscape and Turf Pest Management Handbookshould eliminate current infestations. Both yellow-necked and walnut caterpillars feed as a group, so spot treatments or removal of the caterpillars by pruning or physical destruction are the most effective forms of management.

In addition to these common summer defoliators, we have been seeing some damage on willows by spiny elm caterpillars in the Chicago area. The larvae of this caterpillar are black, about two inches long when fully grown, and have white and burgundy spots along their backs. They also have long spines around each segment. An interesting fact about this defoliating caterpillar it becomes the mourning cloak butterfly. For some people, this poses a dilemma: What is more important--the appearance of the plant or the beauty of the insect?

Author: John Lloyd


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