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June 16, 1999

Oak slug sawfly larvae are numerous on red oak at The Morton Arboretum in northeastern Illinois. They are called slug sawflies because the larvae have a superficial resemblance to slugs. They grow to about 3/4 inch long, are pale yellow, and are covered with a translucent slime. Because these insects are gregarious, the entire group of young larvae will likely be located on just one or two leaves that can be removed, ridding the tree of the entire infestation in the process. Many labeled insecticides are effective.

Bagworms have hatched throughout southern and central Illinois. Remember that control is most efficient if you wait for about two weeks after the caterpillars hatch. This allows all of the eggs to hatch and the caterpillars to finish blowing from tree to tree.

Adult Japanese beetles should be present in the Collinsville area as well as other areas of infestation in southern Illinois. They should show up in the rest of Illinois by the end of June. There are indications that Japanese beetle adults are attracted to previous feeding damage so control in these early days of infestation may reduce later damage.

Author: staff at The Morton Arboretum


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