Cape Elizabeth tree warden Todd Robbins stands on Charles Jordan Road, where trees that normally form a shady canopy have been damaged by winter moth caterpillars. An aerial survey of the town conducted last year found 300 acres of dead oak trees. Staff photo by Shawn Patrick Ouellette

CAPE ELIZABETH — The destruction wreaked by winter moth caterpillars is readily visible along many roads in this rural seaside town, especially along Route 77 as it sweeps by Ram Island Farm, Crescent Beach State Park and Kettle Cove.

What normally would be a thick green canopy over Charles E. Jordan Road, near the historic Sprague Hall Grange, is a lacy wisp of tattered leaves that allows early morning sunshine to beat on the black pavement.

The leaves are so damaged, trimmed to their veins and midribs, Todd Robbins, the town’s newly appointed tree warden, must examine the bark of each tree before confirming that they are oaks.

“It’s a dire situation,” Robbins said. “Thousands of trees are affected here and it’s working its way into South Portland and Scarborough.”

Winter moth larvae begin feeding before the buds expand. This photo taken in May 2012 in Harpswell shows larvae several weeks into their development. Photo by Charlene Donahue/Maine Forest Service

Cape Elizabeth is the hardest hit by an insect infestation, first identified in 2011, that is damaging and killing oak, maple, elm, ash, apple and other fruit trees in coastal Maine communities from Kittery to Bar Harbor, the Maine Forest Service says.

An aerial survey last year found 300 acres of oak mortality in Cape Elizabeth, an area encompassing 2,000 to 3,000 dead trees and the only place in Maine where winter moths are known to have killed trees, said Charlene Donahue, a state forest entomologist.

A flyover last week confirmed that the winter moth infestation has spread into South Portland and Scarborough. Still, Donahue sounds more hopeful than Robbins.

“It’s spreading slowly,” she said. “I’m actually pleased and surprised that it’s not moving faster than it is. It didn’t look as bad as it did in 2016, but it has spread somewhat into South Portland and Scarborough.”

TREE WARDEN’S CONCERN

Robbins, a licensed arborist, isn’t new to the winter moth problem. He’s been dealing with it for several years as assistant property manager of the 2,100-acre Ram Island Farm, which includes a variety of orchards and forested areas.

Robbins is raising the alarm now, in his part-time role as tree warden, as he tries to assess the breadth of damage to municipal trees and provide town officials with a recommended course of action when they meet later this summer.

While it promises to be a costly proposition to remove and possibly replace hundreds of dead trees along town roads, the threat to Maine’s apple, cranberry and wild blueberry crops could be even greater.

“This is not just a homeowner problem, this is a concern to the agricultural sector as well,” Donahue said. “This potentially could be very serious for blueberry growers because (the bushes) flower when the caterpillars are feeding, so they can’t spray them with insecticides that would kill bees.”

Named for their habit of emerging November through January, the small off-white moths came to North America from Europe in the early 1900s. Infestations were seen first in Nova Scotia in the 1930s and then in the Pacific Northwest in the 1970s, according to the forest service. The moths arrived in Massachusetts in the early 2000s, spreading south into Rhode Island and north into Maine.

Entomologists believe the moths were brought here when people transplanted perennial flowers and shrubs from infested gardens to the south. The spread continues in much the same way, especially among gardeners who like to swap plants with friends or sell them at yard sales or fundraisers.

“It’s being spread mostly by landscaping material,” said Robbins, noting that lawn care and landscaping companies add to the problem when they dispose of contaminated dirt and yard waste in other communities or at municipal composting facilities.

While the winter moth problem was first recorded here in 2011, Robbins believes it started much earlier. He has examined the outer rings on freshly cut stumps of dead trees and found little growth in the last eight years and evidence of tree rot in the first few inches beneath the bark.

“Normally, trees die from the inside out,” Robbins said. “These trees are dying from the outside in.”

WINTER MOTH CYCLE

The caterpillars start feeding in May, just after trees have put out leaves and when outdoor temperatures hit the low 50s, Robbins said. If a tree loses a significant amount of foliage, it will try to put out a second set of leaves, diverting energy from the usual growth process and further weakening the tree.

“The growth process goes into hysterics,” Robbins said. “As an arborist, it kills me to see this.”

Winter moths emerge from the ground in early winter, when they leave the pupal state to mate and lay eggs. The moths seen flying around porch lights and street lamps are male. In heavily infested areas, they can form huge clouds that make it look like as if it’s snowing.

The female moths have vestigial wings and are flightless, so they crawl up tree trunks and lay their eggs in crevices in the bark. They prefer oak trees but also will infest maple, ash, elm, aspen, cherry and apple trees, and cranberry and blueberry bushes.

The moths die soon afterward. The eggs can survive the harshest winter weather. Defoliation follows the next spring, when the green, hairless caterpillars hatch from the eggs and feast on leaves before dropping to the ground to begin the pupal stage and form cocoons.

The forest service has taken steps to control and reduce winter moth infestations, and there are signs that the effort might be successful.

Funded by the federal government, the agency released parasitic flies in several locations in recent years, hoping to copy successful moth population reductions in Nova Scotia. Thousands of flies were released in Cape Elizabeth and Harpswell in 2013, Kittery Point, Harpswell and Vinalhaven in 2014, and Cape Elizabeth and Peaks Island in 2015.

The flies lay eggs on leaves that are eaten by winter moth caterpillars. The fly eggs hatch into maggots and lay dormant inside the caterpillars until late summer, when they eat the moth larvae as they pupate underground.

“The flies have already been established in Kittery and Cape Elizabeth, so that’s a good sign,” Donahue said. “Hopefully it will work over time.”

‘DON’T PANIC, PAY ATTENTION’

Donahue said homeowners who suspect they have a winter moth infestation needn’t worry about their trees until they lose half of their foliage.

“Trees can take three to four years of complete defoliation before they die,” Donahue said. “If you lose more than half of your leaves one year, you should take steps to protect the tree the next year. Don’t panic, just pay attention.”

One option is to spray a mineral-based horticultural oil, available at garden centers, on trunks and branches in late winter or very early spring, before leaves begin to bud. The oil smothers the caterpillars.

Bacteria-based pesticides also may be used to kill the caterpillars, although they may harm other moths, butterflies and bees, according to the University of Massachusetts Center for Agriculture, Food and the Environment. In the fall, some people wrap tree trunks in sticky bands, also sold at garden centers, that trap the female moths as they climb.

To fight the winter moth problem on a broader scale, Robbins said all homeowners should consider planting native trees that aren’t susceptible to winter moths and other pests. He said one of his biggest frustrations is that some town residents have continued to plant oaks, maples and other nonnative trees in recent years, and now they’re calling him to find out why they’re dying.

He recommends planting a variety of attractive, indigenous trees that will help to create a more diverse, disease-resistant landscape, including hickory, sycamore, sassafras, black gum, catalpa, hornbeam and linden trees.

“Stop planting oaks and maples,” Robbins said. “We’ve created a monoculture and this is what happens.”

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