How to ward off gypsy moths

An example of what gypsy moths can do to leaves.
An example of what gypsy moths can do to leaves. Suzanne Kreiter/Globe staff

They’re hatching in May, and they’re coming for your trees. Despite their seemingly harmless, fuzzy appearance in the caterpillar stage, gypsy moth larvae cause mass defoliation during their spring feeding period.

Last year, the leaf-munching caterpillars left behind about 923,000 acres of damage statewide, according to the Massachusetts Department of Conservation and Recreation.

Normally, the entomophaga maimaiga fungus naturally reduces the gypsy moth population. But due to drought conditions in 2015 and 2016, the fungus wasn’t as prevalent, which led to an outburst in the gypsy moth population in the last two years.

“We’re predicting this year to be not nearly as bad,’’ DCR forest health program director Ken Gooch said, based on an egg mass survey that was conducted in October. The fungus and nuclear polyhedrosis virus (NPV) kicked in last year, Gooch said, killing many of the caterpillars before they could lay eggs.

But the threat to foliage remains. Kevin Narbonne, a certified arborist and assistant district manager of Hartney Greymont tree services, said moths could still cause some damage this year.

“I’ve seen some years where we think it’s going to be low numbers [of moths], and all of a sudden there’s an upswing— in temperature, in the environment— and you get defoliation,’’ he said.

Each female lays one egg mass, which can contain 100 to 300 eggs, Gooch said. Repeated defoliation coupled with drought conditions makes trees weak.

“There’s not really a whole bunch a homeowner can do,’’ Gooch said, other than taking a few preventative measures.

According to Gooch, arborists are predicting that gypsy moths will be most concentrated in these pockets of the state: the Connecticut River Valley, north of the Quabbin Reservoir, the South Shore, and Essex County.

Here are some tips to protect the trees on your property.

Keep an eye out for eggs.

Gypsy moths lay egg masses on trees, as well as on backyard furniture, sheds, and even wheel wells of cars. They gather pretty much anywhere that is secluded and shaded, said Russell Holman, consulting arborist at Hartney Greymont.

The masses are the color of a brown paper grocery bag, and measure about an inch and a half long and up to an inch wide, according to Holman.

Take action.

If you find an egg mass, Gooch said, you can scrape it off and destroy it by placing it in a mixture of dish soap and water.

You can also call your local arborist for advice. “Make sure they are a certified arborist,’’ Gooch stressed.

Also consider how your trees fared last spring. “If the tree was defoliated last year, it’s important to treat it this year,’’ Holman said.

A certified arborist will determine the best course of action. Some will spray a pesticide on the tree canopy to fend off the moths.

Depending on how early you take action, some arborists use bacillus thuringiensis (b.t.), a type of bacteria. This biological pesticide is very specific to gypsy moth caterpillars – it will not harm the tree or other insects, such as bees, Gooch said.

Some homeowners band their trees in burlap or similar materials to trap the caterpillars. However, Gooch calls this a “feel-good’’ measure. Tree banding usually isn’t effective, especially if you don’t have the time to change the wrapping frequently, Holman added.


It is also important to tend to your tree’s general health. This means fertilizing, pruning, mulching, and watering. This helps trees recover faster from defoliation.

“A healthy tree is able to withstand limited defoliation,’’ Gooch said.

Nicole DeFeudis can be reached at nicole.defeudis@globe.comSubscribe to our free real estate newsletter — our weekly digest on buying, selling, and design — at