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Browntail moths: Snip those webs. Now.

Toxic pest infestation is spreading in Waldo County. We can slow it down.
By Carolyn Zachary | Apr 01, 2020
Courtesy of: Morten Moesswilde, Maine Forest Service Browntail moth web in a fruit tree beside a parking lot. Note the silky “hold-fast” at the base of the web.

The next few weeks could well be the last chance to make a serious dent in the spreading toxic browntail moth population in the Midcoast. Caterpillars are still tucked away in grayish-white winter webs in their preferred trees: oak, elm, birch, poplar, apple and other fruit trees.

The webs are easy to spot, securely anchored to branch tips by a thick white “hold-fast.” Almost as thick as a piece of yarn, the silk strand bundles together web-enclosed clusters of leaves and attaches the web to a twig. This spring, Maine Forest Service officials say, the webs are widespread in Waldo County — with infestations rated from moderate to high along roadways, in the woods, rimming parking lots and playgrounds, around homes.

Now is the time to rid trees of the webs, save foliage and perhaps the trees themselves, and prevent nasty summer rashes from toxic hairs on the caterpillars, in their webs — even in the air. The webs can be found anywhere the caterpillars have overwintered — including on the undersides of decks and outdoor furniture, beneath roof overhangs, around barn and garage door frames.

Forest Service officials urge action now, especially in public areas like parks, athletic fields and business and professional office parking lots. Not only are the browntail moth’s toxic hairs a menace that delivers an itchy, painful rash; the caterpillars are travelers. Customers, clients, patients and families that park in public places often unwittingly carry these hairy travelers to other locations, effectively spreading the infestation.

“We just finished the (Waldo County) browntail moth survey last week, and we’re going to create a risk map this week,” Tom Schmeelk, an entomologist with the Maine Forest Service Insect & Disease Lab, said Monday. “It looks like there’s going to be a pretty high population, if not worse than last year, especially in Lincolnville and along Route 3 approaching Belfast — there are a bunch in trees lining that Route 3 corridor.”

He listed Appleton, Camden and Rockport as other areas with serious infestations.

District Forester Morten Moesswilde of Belfast first saw browntail moth webs in Waldo County in just two or three locations about three years ago. Initially, he noticed them in two or three apple trees in Palermo and a few trees in Belfast. “The situation now has gone completely to the other end,” he said. “It’s a very different story, with a lot of webs in a lot of different places.”

Although there are a few webs in Prospect and Stockton Springs, the county's heaviest infestation now runs from Palermo to Belfast, and along the coast to points south, Moesswilde said.

These natives of Europe left behind their natural predators when they migrated to Massachusetts in 1897. But there are ways to stem the spread of browntail moths. The simplest and cheapest is to prune the webs out of trees, drop them into large buckets of soapy water, and let the soap and water kill them.  For webs in tall trees, people are getting creative, Moesswilde said, using combinations of long-handled loppers and roof rakes, for example, to reach webs that are high up.

The webs can also be burned, with caution; burn permits are required.

Browntail moth webs are relatively easy to spot; it’s not necessary “to chop out all the other tent caterpillars that aren’t that big a deal from a forest health standpoint,” Moesswilde said.

“We have roughly two weeks to get them,” he said Monday, urging business owners, homeowners and public works crews to go after them now, especially in areas where oaks, crabapples and other fruit trees are planted.

“Around mid-April, the small caterpillars leave the webs and start foraging on leaf buds to get a mouthful,” he said, “but I wouldn’t give up then until you actually see little leaves. The nights are still cold and they go back to their webs. So early in the season, while nights are cold, if you can clip webs early in the morning, you have a better chance.

“Sooner is always better,” he said. And even small webs count — a single web can contain anywhere from 25 to 400 of the pests.

There are other eradication methods. The most common and cost-effective, according to Schmeelk, is tree injections. Arborists have pressurized systems. They drill small holes into the trunk, 4 to 6 inches apart around the tree, plug into the holes and pump insecticide up into the tree.

Do-it-yourselfers can obtain little capsules of insecticide, available at hardware stores and online, drill holes, insert the capsules and let the rising sap take the contents up the tree to its buds.

He, too, urged the public to treat infested trees, especially in high-traffic areas, “like hanging over your house.” Arborists also can clip webs, and even bring in “cherry pickers” to reach the tops of towering oaks.

Schmeelk does not encourage cutting down trees to get to the webs. “Removal is a one-and-done solution,” he said, “but it’s a permanent solution to a temporary problem.”

Once temperatures stabilize at about 50 degrees, caterpillars will have vacated their winter webs, he said.

One ray of hope: There is a fungus, Entomophaga aulicae, that attacks browntail moths. Prevalent in Southern Maine during the cool, wet spring last year, it wiped out a chunk of the browntail moth population in Yarmouth, Cumberland and Freeport, Schmeelk said.

The downside: That same cool damp weather promotes needle cast fungi, which cause thinning crowns — a premature loss of needles — on white pines, Moesswilde said.

Bottom line: Start clipping. Now.

For more information on browntail moths, visit maine.gov/dacf/mfs/forest_health/invasive_threats/browntail_moth_info.htm or go to frequently asked questions at maine.gov/dacf/mfs/forest_health/invasive_threats/browntail_moth_faqs.htm

 

Browntail moth webs stand out against the sky atop an apple tree by the road in Liberty. (Courtesy of: Morten Moesswilde, Maine Forest Service)
A heavy infestation of browntail moth caterpillars in a stand of oak trees in June. Caterpillars are large, with tons of hairs, and nearly complete defoliation of the oaks. Note the distinguishing two orange dots. (Courtesy of: Morten Moesswilde, Maine Forest Service)
Pruned webs in a pail, waiting for soapy water. (Courtesy of: Vinalhaven Land Trust)
Browntail moth webs crown a tall oak tree in a Waldo backyard March 31. Too high up for loppers to reach, the webs' caterpillar occupants can be killed with insecticide injected into the tree. (Photo by: Carolyn Zachary)
Browntail moth caterpillar in June. Note the two distinctive orange dots. (Courtesy of: Morten Moesswilde, Maine Forest Service)
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