Pesticide spray to combat invasive moths set for next month in St. Clair County

A round of aerial treatment to prevent the spread of the invasive spongy moth is set for several parts of St. Clair County next month, two years after the species’ caterpillars wreaked havoc on local foliage.

According to the county, the spongy moth suppression program will kick off in mid-May, delivering spray for areas in Clyde, Columbus, Fort Gratiot, Kimball, and St. Clair townships. Application dates will be determined weather permitting and by caterpillar development as spring ensues.

Originally working with Friends of the St. Clair River, the county dedicated $550,000 for spraying a biological pesticide over 5,100 acres of tree-heavy areas last year following more than 800 complaints from residents in 2021 over an infestation of moth caterpillars — renamed spongy from the previous derogatory label “gypsy.”

This year, the county is set to spend $30,000 to spray over 320 acres after 400 reports of moth issues. That’s a cost of roughly $95 an acre. It involves no cost-share with local communities.

The treatment date will be posted at www.stlcaircounty.org/caterpillars once determined.

The biological control Btk, or bacillus thuringiensis var. kurstaki, is being used for the spray. According to a news release, it’s an organic water-based insecticide aimed to have a low impact on residents, pets, and wildlife.

Weather parameters for spraying include average wind speeds of less than 10 miles an hour and relative humidity of more than 50%. Spay operations typically begin in the early morning and continue until completed.

For more information, contact gypsymoth@stclaircounty.org, call (810) 989-6217, or visit the county’s caterpillar page.

Contact Jackie Smith at (810) 989-6270 or jssmith@gannett.com. Follow her on Twitter @Jackie20Smith.