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June 10, 2003
Hatched bagworms were found in Mt. Vernon in southern Illinois on June 2. They will probably hatch in central Illinois about 2 weeks later. Newly hatched bagworms crawl to the tops of trees, spin out long silk strands, and sway in the wind until they are blown free to float, for hundreds of feet to many miles depending on updrafts and wind speed. Because the caterpillars are small, they cause little damage to foliage, feeding on epidermis and underlying mesophyll tissue, causing light areas on the foliage.

Waiting to spray an insecticide for at least 2 weeks after egg hatch allows sufficient time for the bagworms to finish their ballooning and settle down to feed. One application at that time provides a high level of control. Spraying before the ballooning has finished results in additional larvae coming onto treated trees, frequently after spray residue has broken down, requiring a second spray for tree protection. Cyfluthrin (Tempo), spinosad (Conserve), and Bacillus thuringiensis kurstaki or Btk (Dipel, Thuricide) are very effective.

Mimosa webworm should be appearing as first-generation caterpillars. Look for light-colored areas of foliage on honey locust and silk tree (mimosa). Close examination reveals green to brownish caterpillars causing window-feeding in silk-tied leaflets. This insect is less common after very cold winters. Although last winter had prolonged cold, the minimum temperatures were probably not low enough to greatly reduce the populations. Many insecticides are effective. The secret to effective control is recognizing the young webworms in this first generation and reducing their numbers so that the second generation is not large enough to cause serious aesthetic damage.

Mosquitoes are very numerous throughout Illinois. The predominant species at this time of year are floodwater mosquitoes, particularly Aedes vexans, which hatch from eggs laid in low-lying areas. Spring rains flood these areas, resulting in egg hatch. Although this species tends to be noisy, and painful biters, they are not likely to carry West Nile virus and other diseases. The disease-vector mosquitoes are much more common later in the summer when it is hot and dry. Repellents containing DEET are very effective against these and other mosquitoes. A concentration of about 30% DEET provides a combination of high effectiveness and longevity.

Author: Phil Nixon


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