Following defoliation by gypsy moth caterpillars last year across much of the northern Lower Peninsula, Michigan residents across the state may begin to notice leaf loss on oaks, aspens. and maples again this year.
Gypsy moths are an invasive species, a term for non-native pests that can harm native species and ecosystems. In the caterpillar stage, the insect is a voracious eater of leaves. 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 could cause more caterpillars to hatch this spring in localized areas of the Lower Michigan.
Last year, defoliation was most severe in Alcona, Alpena, Montmorency and Oscoda counties, with more localized outbreaks from Manistee south to Newaygo County. Forest health experts from the Department of Natural Resources say gypsy moth caterpillar populations are likely to collapse in some areas while they thrive in others. Significant defoliation is likely to become visible over the next month in localized outbreak areas and persist until mid-July.
“Gypsy moth caterpillars rarely kill trees in Michigan,” said James Wieferich, MNR forest health specialist. “Only stressed trees with problems such as 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 homes and yards than in the woods.
Leaf-eating caterpillars are hairy, up to 2 inches long, and have a pattern of blue and dark red spots. Male butterflies are dark buff in color and fly; females are white with black, wavy markings and do not fly.
Keep trees healthy to help fight gypsy moth defoliation
The best thing people can do to reduce the effects of pests like gypsy moth on their trees is to promote tree health.
“Water the trees regularly and avoid damaging the roots and bark,” Wieferich said. “It greatly helps trees repel the effects of defoliation. “
Mature forests can normally withstand heavy gypsy moth defoliation with little impact. Defoliated trees will begin to develop new leaves in July to replace those that have been eaten. Even severely defoliated trees will recover without serious long-term effects. However, consecutive years of massive defoliation will begin to wreak havoc, even on the healthiest mature trees.
Parasites were discovered in Michigan in 1954
Gypsy moths were first discovered in Michigan in 1954. In the 1980s and 1990s, large populations of gypsy moths roamed Michigan, defoliating up to a million acres in some years, said Scott Lint, an expert on gypsy moths. MNR Forest Health. At that time, moths were new to the state and the population grew rapidly without natural control from parasites, predators, and pathogens.
In 1991, a fungal pathogen that killed gypsy moth caterpillars in the northeastern states was deployed to Michigan. This fungus, Entomophaga maimaiga, has been shown to be an effective means of biological control, remaining in the soil from year to year and infecting gypsy moth caterpillars that come into contact with the soil or with other infected caterpillars. Moist soils help activate the fungus and spread it among gypsy moth populations.
The nucleopolyedrosis virus is a naturally occurring virus that kills caterpillars. NPV can spread rapidly during major gypsy moth outbreaks, causing the population to collapse. This virus was also distributed artificially in Michigan in the 1990s with positive effects.
To determine if NPV is at work in a certain location, look for dead caterpillars attached to tree trunks in an upside down “V” position. Caterpillars affected by the fungus E. maimaiga also remain attached to the trunks but hang downwards.
These natural enemies of the gypsy moth are now well established throughout Michigan and are actively reducing populations. To date, these pathogens have limited the size and duration of outbreaks to just a few years, eliminating the need for spray programs.
Various Ways To Deal With A Gypsy Moth Outbreak
For residential areas, several Michigan counties, local governments, and / or landowner associations conduct fall surveillance to determine if populations are reaching epidemic levels. If treatments are required, an aerial application of pesticides will target heavily infested areas.
Michigan communities considering a gypsy moth spray program should seek licensed pesticide application companies with knowledge of complex pesticide laws, including notification and permit requirements.
A list of Michigan companies licensed to apply pesticides is available at Michigan.gov/MDARDPABL. Additional information on pesticide laws and regulations can be found at Michigan.gov/MDARDPestCert.
To control a gypsy moth infestation in a handful of individual trees, homeowners can purchase a spray containing Bacillus thuringiensis var. kurstaki, a bacteria naturally present in the soil but which can be fatal to some caterpillars and moths. The best time to spray is when the caterpillars are small, usually mid-May to early June. If you do decide to apply pesticides to your 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. Meanwhile, spraying the caterpillars with a mixture of dish soap and water or scraping the caterpillars in a bucket of soap and water can also be effective.
To learn more about gypsy moth caterpillars, visit the MSU Extension website. More detailed information is available in this MSUE bulletin which covers Btk management for gypsy moth.
For more information on the DNR’s Forest Health Program or to view last year’s Forest Health Highlights report, visit Michigan.gov/ForestHealth.