The Year of the Gypsy Moth

The Year of the Gypsy Moth

All around Chittenden County, landowners and users of natural spaces are reporting an increase in the presence of Gypsy Moth caterpillars.  Some reports document only a few, while others share stories of swarms that are defoliating huge swaths of trees.  The City wanted to share all of the information it is aware of at this time in case residents have questions or concerns. 

According to Craig Lambert, the City Arborist, defoliation in South Burlington is mostly concentrated in areas with a lot of mature oaks, primarily in the vicinity of the airport.  It is important to note that historically, gypsy moth outbreaks in this area used to occur in a 7-8-year cycle.  The Entomophaga fungus has kept this species in check over the past 30 years, but this year, this fungus has been inhibited by dry conditions.

Ethan Tapper, the Chittenden County Forester, has released the following information on this year’s outbreak, including what landowners can do and what the state may do in the future.  The Vermont Department of Forests, Parks, & Recreation has also shared a blog with similar information.

The hope is that next spring will be wetter, which would bolster the fungus that keeps the Gypsy Moth caterpillar population in check.  If you have questions about potential infestation of trees on your property, please contact Craig at:


Excerpt from Ethan Tapper, Chittenden County Forester:

If you’ve been experiencing a plague of caterpillars defoliating your trees, you’re not alone. I’ve been getting reports from all over the Champlain Valley (in Chittenden County I have reports from Hinesburg, Williston, Essex, Milton and Colchester) of a gypsy moth outbreak – what seems to be the first outbreak of this non-native insect in Vermont since 1991. Gypsy moth caterpillars often defoliate oak species, although they are known to feed on more than 300 species of trees and shrubs including maples. They can create a nuisance for homeowners, from the sights of caterpillars climbing the sides of residences and falling excrement to the sounds of chewing on leaves.

The gypsy moth (Lymantria dispar) is native to Europe and was introduced to Massachusetts in 1869. Its population in Vermont is generally mitigated by a fungus (Entomophaga maimaiga), which may be being suppressed by droughty conditions over the last few years. While in Vermont, gypsy moth is known to be generally non-fatal to trees, repeated defoliation can kill trees – in more southerly portions of its range it is known to cause widespread mortality. US Forest Service has a short podcast that can give you a quick rundown on the history of the gypsy moth and it’s relationship to Entomophaga at:

There are a few treatments that could be effective for protecting your trees from gypsy moth defoliation – most are more practical for protecting a few trees rather than a whole forest. The most commonly recommended pesticide treatments contain the bacteria, Bacillus thuringiensis kurstaki (Btk). Btk is applied to foliage where gypsy moth larvae will consume it and are then killed. This strain of bacteria is specific to moth larvae, and its toxic properties get activated when it interacts with particular enzymes in the caterpillar’s digestive tract. You can find a certified arborist (and certified pesticide applicator) who can help you with applying Btk via the following website:

Gypsy moth feeding will continue through the growing season and more reports of defoliation are expected. To learn more about management options (and gypsy moth in general) check out the resources at:

The good news is that the defoliation will likely be over by the end of June, and that if this is your first year of major defoliation your trees will likely re-sprout leaves and survive. Although gypsy moth caterpillars are damaging, otherwise healthy trees can often survive a few years of successive defoliation. Defoliation and drought conditions, can combine to stress tree health and vigor.  Due to this combination of stressors, Vermont may see another year or two of high levels of gypsy moth activity unless the state sees some rainy seasons to increase the population of Entomophaga.