Gypsy moth numbers increasing in southern Michigan

Gypsy moth caterpillar feeding on oak leaf.

Gypsy moth caterpillar feeding on oak leaf. Photo by Clifford Sadof, Purdue University.

Gypsy moths are an invasive species, a term used for non-native pests that can cause harm to native species and ecosystems. During it’s caterpillar life stage, the insect caused widespread damage to defoliation in Michigan from the mid-1980s to the early 1990s. A large population in 2018 has led to more caterpillars hatching this spring. The defoliation is heaviest in Barry, Ionia and Washtenaw counties but MDNR forest health experts say that its likely that gypsy moth caterpillars are causing similar problems on a local scale in other areas of the Lower Peninsula. Heavy defoliation will likely become visible within the next few weeks in localized outbreak areas and persist through mid-July.

Forest health expert, James Wieferich says, “gypsy moths rarely kill trees in Michigan. 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 than in the woods.”

Defoliation most often occurs in the season following a drought-heavy year, such as 2016, 2017 and the summer of 2018. Many forest pests tend to target trees that are weakened – perhaps from drought – or otherwise not in the best of health.

The leaf-eating caterpillars are hairy, up to 2 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.

How to Protect your Trees from Gypsy Moth 

Weiferich says you can help promote tree health by “watering trees regularly and avoid damaging the roots and bark. Doing these two things will help the trees fend off the effects of defoliation. You can also remove dead and dying trees in a woodlot periodically as this will help the remaining trees stay strong.”

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.

More detailed information is available in this MSUE bulletin that covers the Btk management for gypsy moth.

Original article by James Wieferich, MDNR

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