Gypsy moth has been a forest pest in Michigan for over 40 years. Over the last several years, the population and effects of gypsy moth have been higher in Grand Rapids than previous years. This has mainly affected areas with high oak tree populations. Below, we've explained the situation, our plan of action, and what you can do to help.
Our forestry team performed gypsy moth egg mass surveys and counts throughout Grand Rapids in the fall of 2018. We found gypsy moth populations above a threshold density of 1,000 egg masses per acre in several locations. These include Ken-O-Sha Park, Shangri-La neighborhood, Plaster Creek Trail, Covell Avenue, Ball Avenue and Woodlawn, Oakgrove and Oakhill Cemeteries. If you would like to see the egg mass density map, click here(PDF, 691KB) .
The gypsy moth population in Grand Rapids grew quickly because of dry spring seasons in 2016 and 2017. If conditions remain wet this spring, we expect the population to crash as a naturally occurring fungus that kills gypsy moth caterpillars known as Entomophaga Maimaiga, will likely spread among them. In addition, a virus called Nuclear Polyhedrosis Virus (NPV) naturally builds up in high density gypsy moth populations, causing populations to crash once they have reached high levels.
While relying on natural predators is recommended by experts, providing some control strategies on public and private properties for isolated populations can be effective. We're partnering with Friends of Grand Rapids Parks to train Neighborhood Forester volunteers. These training sessions will teach volunteers about gypsy moth egg mass scraping and how to apply tree bands to stop caterpillars from moving up the tree. We're also planning a spring application of Bacillus thuringiensis (Bt), a microbe found in soil that is toxic to the gypsy moth caterpillars.