It may be July on the Vineyard, but in parts of Oak Bluffs, motorists are passing by winter scenery. Dozens of oak trees along County, Barnes, and Wing Roads are completely leafless. Scores more are partially denuded and riddled with insects. Local experts said the culprits appear to be gypsy moth caterpillars, a well-known pest in Massachusetts that favors eating oak leaves.
Jeremiah Brown, West Tisbury tree warden and lead foreman at Vineyard Gardens, said the state of the oak trees at the intersection of Barnes and County Roads is “the worst I’ve seen anywhere on the Island.” That includes his home in West Tisbury, where he’s been sweeping caterpillar droppings known as “frass” off the floor of his outdoor shower.
Mr. Brown called the gypsy moth infestation at his property minor and not worthy of intervention. Moreover, he said in the few hot spots he’s seen across the Island, the caterpillars have begun to pupate, to enter a cocoon-like stage before they become moths, and that most of their munching is done for the year.
According to Tawny Simisky, an entomology specialist at the University of Massachusetts, the commonwealth has seen an uptick in gypsy moth damage. “Last year gypsy moth defoliation was on the rise — this year it may be even more so. This is likely due to successive dry springs,” she said.
Ms. Simisky said ample rain in April and May serves to activate a soil-borne fungus called Entomophaga maimaiga in time to prevent that season’s caterpillars from extensively defoliating host trees. The fungal spores are lethal to the caterpillars. Entomophaga maimaiga is not native to the United States.
“It was introduced into the U.S. around 1910 as a method of biological control for gypsy moths,” she said.
Like the fungus imported to combat them, Ms. Simisky noted, gypsy moths are also not native to the U.S., but they do have Massachusetts roots. In the 1860s they were inadvertently released in Medford via France, by Etienne Leopold Trouvelot during a failed study to find an alternative source of silk.
They’ve been a serious and recurring problem in the Northeast ever since then, and reared up in an especially bad outbreak roughly three decades ago, according to Polly Hill Arboretum curator Tom Clark.
“This insect was really at its zenith in the early 1980s. Vast acreages of oak were just wiped out. I remember in June and July going up to New Hampshire and just seeing mountainsides devoid of leaves. It looked like winter basically.”
Mr. Clark was saddened but not surprised by the damage in Oak Bluffs.
“They’re voracious caterpillars,” he said. He added that a defoliated oak tree often has the capacity to recover, but it’s not a given that it will do so.
“The tree is usually able to leaf out again, but it takes tremendous reserves from the roots to do that, and given the season we’re having this year where it’s very dry, that’s another stress added to the tree.”
Mr. Clark emphasized that trees heal slowly from heavy damage. Like many Island trees, the oaks ostensibly besieged by gypsy moth caterpillars in Oak Bluffs may still be in recovery from trauma from another caterpillar, the fall cankerworm, that clobbered Island trees between 2005 and 2007. Also the trees could suffer from cynipid gall wasp infestations. If so, any combination of those stresses may “tip them over the edge,” he said.
Topping off the list of environmental abuses these oaks may have endured are a few they may yet have coming. Ms. Simisky said that trees weakened by gypsy moth defoliation may be at greater risk of being attacked by pests and pathogens like various boring beetles and root rot.
Oak Bluffs isn’t the only place enduring heavy gypsy moth caterpillar damage.
David Chalker, an arborist for Bartlett Tree in Osterville, told The Times that Plymouth, parts of Mashpee, and a sizable portion of the Lower Cape have been hit hard by gypsy moth caterpillars this season. Mr. Chalker said oaks took the brunt, but in several instances, the caterpillars ate all the oak leaves available to them and moved on to strip white pines, pitch pines, and spruce. He suspected those three types of conifers will suffer a higher mortality than the oaks.
“It’s much more difficult for them to rebound,” he said.
For Islanders whose trees may have been damaged by gypsy moth caterpillars, Mr. Chalker, Mr. Brown, and Mr. Clark all felt it was too late to employ controls like Bacillus thuringiensis or BT, a commonly employed bacterial insecticide. They consider the caterpillars to be all but done eating for the year. Regardless of the size of the tree, they pointed to watering as the single most beneficial action that could be taken to bolster a defoliated tree’s health, especially during the current dry spell.
Mr. Brown said even large old trees you may have in your yard, ones that you may never have felt the need to tend to and that may not be infested with anything, could use a hose running under them, given the overall lack of rain.
Mr. Chalker advised watering at dusk to hedge against evaporation. He also said not to skimp, but to soak deeply. “Water the hell out of the plant,” he said.
For more information on gypsy moths, Ms. Simisky recommended visiting the University of Massachusetts agricultural website, ag.umass.edu/landscape.