Trees encased in webbing in early June: What happened?

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Mark Frever, grounds supervisor at Albion College, the Oakland County Extension horticulture staff, and several others called me last week to ask what is going on with these trees encases in webbing. Fortunately, they also sent me some excellent photos that showed trees completely webbed over with clumps of light green caterpillars with black spots hanging from the webbing. The culprit is the euonymus caterpillar, another exotic insect pest from overseas. This one comes from Europe.

We have had euonymus caterpillar in Michigan for at least 20 years. Fortunately, the caterpillars are almost entirely restricted to Euonymus europaeus, known as common spindle tree. (see photos)This tree grows 12 to 30 feet tall. The leaves turn yellow-green to reddish-purple in the fall, sometimes rivaling burning bush in fall splendor, but with a much lighter purple-red color. I thought most of the spindle trees were already gone, having been defoliated by euonymus caterpillar each year until they died. But from the phone calls and photos, I see we still have quite a few left.

Spindle trees can usually survive one year of complete defoliation, but may succumb in the second or third year. In order to protect them from the caterpillars, professional landscapers can spray them with a pyrethroid insecticide in mid-May, and homeowners can spray them with Sevin, Orthene, Bayer Multi-Insect Killer. Spindle trees can be very attractive and worth saving, but they will need spraying each year in May for Euonymus webworm.

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