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Experts predict fewer spongy moths on Michigan trees this summer

Michigan Public | By Taylor Bowie

Published May 9, 2023 at 11:41 AM EDT

A band of painter's tape around a tree trunk is used to trap some later instar spongy moth caterpillars, showing their distinctive red and blue dot pattern.

Experts are forecasting a decrease in spongy moths in Michigan.

The invasive species is known for eating tree leaves throughout the spring and early summer, especially oak trees.

Joanne Foreman is the invasive species communication specialist for the Michigan Department of Natural Resources.

“The cycle of the caterpillars eating lasts only about six to eight weeks. If a deciduous tree loses a lot of its leaves during that time, basically the best thing that you can do is just make sure that tree is getting a lot of regular watering.”

In most of Michigan, the pest's population peaked in 2021. Foreman said some areas will still experience outbreaks of spongy moths, but other populations in Michigan have been curbed by a naturally occurring nuclear polyhedrosis virus and the Entomophaga fungus.

Foreman said the caterpillars usually stop eating leaves in mid-summer, and trees can recover their leaves by July.

She said there are pesticides specifically made for spongy moths that have little impact on beneficial insects, and said those using pesticides should only use those specifically made for spongy moths, and to only apply pesticides on the leaves of trees, not the caterpillars themselves.

Foreman reminded Michigan residents to be cautious when removing egg masses and spongy moth caterpillars as they often nest in difficult to reach places.