Michigan Prepares For The Latest Caterpillar Threat
The list of tree-damaging insects continues to grow in Michigan. The Michigan Department of Natural Resources has just issued a warning about a nuisance caterpillar named the spongy moth caterpillar.
According to Michigan State University’s Enviroweather prediction model, due to warmer temperatures, the caterpillars are beginning to hatch in the Lower Peninsula of Michigan.
There is some good news concerning the latest outbreak. According to James Wieferich, forest health unit manager with the Michigan Department of Natural Resources, the infestation peaked in 2021 and is in the process of declining. Wieferich says,
While spongy moth defoliation will never cease to exist, viral and fungal agents already in the environment are working to control this naturalized pest.
What Do I Do If I Have Spongy Moth Caterpillars On My Property?
- Before hatch: Inspect decks, outdoor furniture, fences, and trees, focusing on your favorite outdoor use areas. Scrape any accessible egg masses into a bucket of soapy water or burn or bury them.
- After hatch: Use a whisk broom to sweep young caterpillars into a bucket of soapy water. Let them soak overnight, then dispose.
- Make a tree trunk trap: Cut a band of burlap 18 inches wide and long enough to go around the tree trunk and overlap a bit. Tie a string around the center of the band to make a two-layered skirt around the trunk. When caterpillars climb trees daily to feed, they will get caught in the band. Scrape them into a bucket of soapy water to kill them.
The Early Sign of Spongy Moth Caterpillars
There is a pesticide that will kill the invading caterpillars but has little impact on beneficial insects. It’s called Btk (Bacillus thuringiensis var. kurstaki). It should be used within one to two weeks of the hatch and applied to the tree leaves, not onto the caterpillars themselves.
The MDNR advises that if you have large trees, it’s best to hire a certified professional for the application of pesticides to the affected trees.
Don’t Panic. The Outbreak Will Soon Pass
The infestation of the spongy moth will collapse in a year or two, even without intervention. Affected hardwood trees will typically re-leaf in mid-to-late July after suffering defoliation.