(CBS DETROIT) – Following defoliation by gypsy moth caterpillars last year across much of the northern Lower Peninsula, the Michigan Department of Natural Resources says residents across the state may start to notice the loss of leaves on oak, aspen and maple trees again this year.

Gypsy moths are an invasive species, a term for non-native pests that can cause harm to native species and ecosystems. In its caterpillar life stage, the insect is a voracious leaf eater.

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Gypsy moth caterpillars have spiky hairs and a pattern of blue and red dots. You may find beads of frass (caterpillar droppings) under trees.

Large numbers of gypsy moth caterpillars caused widespread defoliation in the state from the mid-1980s to the early 1990s. A large population in 2020 may lead to more caterpillars hatching this spring in localized areas across Lower Michigan.

Last year, defoliation was heaviest in Alcona, Alpena, Montmorency and Oscoda counties, with more localized outbreaks from Manistee south into Newaygo County. Department of Natural Resources forest health experts say it is likely that gypsy moth caterpillar populations will crash in some areas while they thrive in others. Heavy defoliation likely will become visible within the next month in localized outbreak areas and persist through mid-July.

“Gypsy moth caterpillars rarely kill trees in Michigan,” said James Wieferich, DNR forest health specialist. “Only stressed trees suffering from problems like drought, old age or root damage are at high risk. In most cases, gypsy moth caterpillars are more of a nuisance in residential areas on houses and in yards than in the woods.”

The leaf-eating caterpillars are hairy, up to two inches long and have a pattern of blue and dark-red spots. Male moths are dark buff in color and fly; females are white with black, wavy markings and do not fly.

Gypsy moth caterpillars can defoliate trees quickly at this time of year.

Keep trees healthy to help them rebound

The best thing people can do to reduce the effects of pests like gypsy moth on their trees is to promote tree health.

“Water trees regularly and avoid damaging the roots and bark,” Wieferich said. “That goes a long way in helping trees fend off the effects of defoliation.”

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Mature forests normally can withstand heavy gypsy moth defoliation with little impact. Defoliated trees will begin to develop new leaves in July to replace those that were eaten. Even heavily defoliated trees will recover without serious long-term effects. However, consecutive years of mass defoliation will start to take a toll, even on the healthiest of mature trees.

Variety of ways to handle a gypsy moth outbreak

For residential areas, several Michigan counties, local governments and or property owner associations conduct surveillance in the fall to determine if populations are reaching an outbreak level. If treatments are needed, an aerial pesticide application will target highly infested areas.

Michigan communities considering a gypsy moth spray program should seek licensed pesticide applicator businesses familiar with the complex pesticide laws, including notification and permitting requirements.

A list of Michigan businesses licensed to apply pesticides is available at Michigan.gov/MDARDPABL. Additional information about pesticide laws and regulations is available at Michigan.gov/MDARDPestCert.

To address a gypsy moth infestation in a handful of individual trees, homeowners can purchase a spray containing Bacillus thuringiensis var. kurstaki, a bacterium that naturally occurs in the soil but can be lethal to certain caterpillars and moths. The best time to spray is when caterpillars are small, usually mid-May through early June. If you decide to apply pesticides on you own property, be sure to choose an EPA-registered pesticide and apply it according to label directions.

Caterpillars move up and down trees, often massing on tree trunks. During this time, spraying caterpillars with a mixture of dish soap and water or scraping caterpillars into a bucket of soap and water also can be effective.

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