Two weeks ago, the North Shore Horticultural Society sent out a call to its membership. The area’s oldest garden club reported that a White Oak memorial tree planted last year in Rosedale Extension Cemetery for the club’s longtime president and auctioneer, Fred Rice, was infected with something called, “Oak Shothole Leafminer.”
It was a sobering reminder of diseases and pests that can take down local trees.
Many remember that in the 1970s, Manchester famously lost nearly all its Elm trees, most of which majestically lined Central and School Streets, from Dutch Elm Disease. In fact, the epidemic was the trigger for the creation of the Manchester Friends of Trees.
Local arborists and tree surgeons say there has been a surge of new and common pests and diseases that deserve public attention. Three significant threats—Oak Shothole Leafminer, Beech Leaf Disease, and Emerald Ash Borer—have popped onto local radars and experts report these challenges may be amplified by climate change.
Oak Shothole Leafminer: A Growing Concern
The Oak Shothole Leafminer (Japanagromyza viridula) is an emerging pest that primarily affects oak trees. This tiny fly lays its eggs on the leaves of oak trees, and as the larvae feed, they create a characteristic pattern of “shot holes.” Over time, these infestations can lead to significant defoliation, which was seen in Fred Rice’s memorial tree on Rosedale. What can’t be easily seen is the significant weakening of a tree when it’s infected, and making it significantly more susceptible to other stresses.
With Fred Rice’s tree, the impact of the Oak Shothole Leafminer was evident.
Norm Weeks of the NSHS discovered the clusters of tiny holes in the leaves. He immediately shared his findings directly with the Manchester Friends of Trees but the biggest comfort came when its president, Jody Morse, brought in Tom Henderson who provided clarity about exactly what was going on. Henderson identified the Oak Shothole Leafminer as the culprit, will see if more damage occurs in the fall, and will treat the tree in the spring. Because it was identified quickly, its prognosis is good.
Beech Leaf Disease: A Looming Threat
Another formidable adversary is Beech Leaf Disease (BLD), particularly targeting American beech trees. While the Oak Shothole is an insect pest, Beech Leaf Disease is caused by a nematode, described as a microscopic worm that landed in Massachusetts three years ago, where it has since surged, said Jack Ingram, Central New England vice president at Bartlett Tree Experts. It causes dark, interveinal banding on the leaves, leading to leaf curling, withering, and premature leaf drop.
“There are a lot of young beech that have been planted in the last 40-50 years. They can be some of the most majestic trees in landscapes, so it’s a real shame that this concern has become so prevalent, especially in Manchester,” said Ingram, adding that local specimens include Native American Beech and the European Beech.
What gets overlooked, especially on Cape Ann, is that beech trees also play a crucial role in our local ecosystems, providing habitat and food for numerous species. As a result, BLD poses a significant threat not just to these trees, but also to the biodiversity they support.
Ingram said BLD has been a big focus for research scientists at the Bartlett Tree Research Laboratories (the research arm of Bartlett Tree Experts). The 117-year-old company has invested significant time and money and expertise in studying BLD and, early this spring, its lab reported the first ever set of Beech Leaf Disease management trials, including the first-ever treatment its research scientists discovered to effectively suppress the disease.
“This disease-causing nematode has spread at an astounding pace, quickly climbing into the ranks of other ecosystem-shifting catastrophes we have seen over the past century, like Chestnut Blight and Emerald Ash Borer,” said Dr. Matthew Borden, a plant pathologist on the research team.
Containment and eradication are no longer feasible, but as part of its study, Barlett’s research team developed a series of Integrated Pest Management (IPM) strategies to treat BLD that it has shared with others in the industry.
“Currently we’re really optimistic about preserving standalone specimen European and American Beech,” said Ingram.
Emerald Ash Borer: A Devastating Invader
Perhaps the most notorious of tree pests, the Emerald Ash Borer (Agrilus planipennis), has been wreaking havoc on ash trees across North America since it was first discovered in Michigan in 2002.
This metallic green beetle, native to Asia, has no natural predators, so its population grows unchecked. The larvae burrow into the bark of ash trees, disrupting the flow of water and nutrients and ultimately leading to the tree’s death, said Mark Cicoria whose namesake tree company has operated on Cape Ann for more than 40 years.
Cicoria said ash trees are relatively common in Manchester, and the recent Emerald Ash Borer has been nothing short of devastating. The pest was confirmed in Essex County several years ago, and since then, efforts to manage its spread have been a top priority for local arborists and conservationists. Strategies include the use of insecticides, biological controls, and the removal of infested trees to protect remaining healthy populations.
The Role of Climate Change
Climate change is amplifying the threats posed by these and other pests and diseases. Warmer temperatures and changing precipitation patterns can create more favorable conditions for the spread and survival of these organisms. Milder winters may not kill off pests as effectively, which can drive larger populations in the spring. Also, trees stressed by drought or big swings in temperature are simply more vulnerable—to infestation, to disease, or simply to delays in normal seasonal behavior.
Changes in seasonal patterns disrupt the life cycles of both trees and pests, and simply stress local trees. A recent example residents may remember, said Cicoria, came in February, 2023, when an unseasonably mild winter averaging around 40 degrees dipped for 24 hours to 10 degrees below zero. The cold snap passed, but in the spring, many area Japanese Maples and Flowering Cherry trees simply didn’t bloom.
“Many people thought their trees were dead,” said Cicoria. “We recommended holding off, and give them a chance to rebound on their own. Thankfully, that year, they did. But it shows the impact of temperature on normal cycles, especially to specimen trees.”
Another species of tree sensitive to the effects of climate change are Birch trees, which Cicoria said are “cold weather trees” and therefore struggle through warm winters.
Cape Ann is not alone. In New England, the effects of climate change are already being felt.
What Can Be Done?
Addressing these challenges requires a multifaceted approach, for sure. Homeowners can help by regularly inspecting their trees for signs of pests and diseases and promptly seeking professional advice if issues are detected. Planting a diverse array of tree species can also reduce the risk of widespread damage from any single pest or disease.
On a broader scale, community efforts to monitor and manage tree health are crucial. Local organizations like the Friends of Trees provide valuable resources and support, like tree planting initiatives, and can research what might be the issue with a particular tree and what management strategies might work.
