In late April the PIDC received a sample and pictures of caterpillars causing impressive damage to a European euonymus windbreak in Dubuque County. We determined that they were a species of ermine moth called the euonymus caterpillars, Yponomeuta cagnagella. This is a European species first reported in North America in 1967 and has been reported sporadically in the Midwest (Wisconsin, Illinois, Michigan) since 1989. Although infestations may have occurred before in Iowa and this is the first time the PIDC has received a sample and photos of euonymus caterpillar.
This year was unseasonably warm so caterpillars were probably active in mid-April, in a normal year early to mid-May would be the time to start scouting for damage. If there are large populations of caterpillars insecticides labeled for caterpillars on ornamental plants, including Bt, can be used to manage the caterpillars. Be sure to read and follow labeled directions. After any insecticide treatment it is also important to check several days later to assess the effectiveness of the treatment and re-treat if necessary.
Webbing from euonymus caterpillars.
Webbing left by euonymus caterpillars on defoliated branches.
Webbing near euonymus.
Webbing left by euonymus caterpillars on non-host plants.
All photos are courtesy of Dennis Hermsen.
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