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Scouting Watch

April 24, 2002

Spring is occurring quickly throughout Illinois with the very warm weather that we have had recently. Insect-development degree days are accumulating quickly, so many spring-occurring insects are showing up. Following are some to be looking for.

Eastern tent caterpillar eggs hatch when the leaves emerge on crabapple. Look for the 1- to 2-inch tents in twig crotches of crabapple, hawthorn, flowering cherry, purpleleaf plum, mountainash, and other Rose family plants.

Cankerworms have hatched throughout the state. Scout for these loopers by striking the branch to see if any drop down on silk threads. Trees that don’t seem to be leafing out are suspect as well because the inchworms may be eating the leaves as they expand. These caterpillars are most common on elm, hackberry, honey locust, and crabapple.

Spruce spider mite and its relatives will be active on spruce, pines, junipers, and other needled evergreens. Hold a white sheet of paper under a branch and strike it sharply. The mites will be knocked onto the paper where they can be easily seen. Slow-moving mites that squash green are spider mites; fast-moving mites that squash red are beneficial predatory mites. There may be enough predatory mites to control the spider mites without spraying.

Hemlock rust mites have been found at the Morton Arboretum in mortheast Illinois. They will cause needles to turn yellow and fall off hemlock, fir, yew, and spruce. Realize that needles that are being shaded out will yellow and fall naturally, so look for symptoms on needles on the outside of the canopy.

Management recommendations for these pests can be found in the Commercial Landscape and Turfgrass Pest Management Handbook, available at your local U of I Extension Office.

Author: Phil Nixon staff at The Morton Arboretum


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