Sinuous galleries created beneath White Ash bark by feeding larvae; several D-shaped exit holes made by emerging adults are also visible. Photo credit Doug Hardy.

Emerald Ash Borer

Emerald Ash Borer — a Destructive Insect Pest Demands Immediate Attention in Norwich

The winter 2024 discovery of emerald ash borer (EAB) in Norwich came as no surprise. Since the 2018 arrival of this non-native beetle in Vermont, where it was first documented in Orange County, it has rapidly spread and is currently known to be present in all of the state’s 14 counties outside the Northeast Kingdom (see map of known infected areas). EAB (Agrilus planipennis) was first found in the U.S. in southeastern Michigan in 2002. Native to Asia and eastern Russia, it is believed to have been introduced as early as the 1990s in solid wood packing material from Asia. Belonging to the beetle family Buprestidae, EAB feeds exclusively on ash trees in the genus Fraxinus. Vermont’s three species of ash — white, black, and green — make up 5-7% of all hardwood trees in the state, with much higher percentages in some areas. As of early 2024, this tiny green beetle has killed millions of ash trees in 36 states and 5 Canadian provinces, causing devastation not seen since Dutch Elm Disease and Chestnut Blight ravaged our streets and forests 50–100 years ago. This invasive insect will inevitably destroy most, if not all, ash trees in Norwich and beyond, posing significant human safety risks, threatening the ecological integrity of our forests, and diminishing a cherished cultural resource.

The ecology and impacts of EAB are well described in various online sources, including an informative fact sheet published by the Vermont Department of Forests, Parks, and Recreation, and a story map from the USDA Animal and Plant Health Inspection Service. Briefly, the half-inch long, bullet-shaped, metallic green adult beetles lay eggs in the crevices of ash bark, where the larvae tunnel into the cambium and feed on the phloem, which is the vascular tissue responsible for transporting nutrients throughout the plant. As larvae feed on this vascular tissue, the tree becomes less able to transport nutrients to the leaves in its canopy, killing the tree from the top down in a span of 2–5 years, depending on its size and health. Infested ash trees rapidly begin to dry out and lose their structural integrity; branch and trunk breakage in diseased ash trees is often sudden and unpredictable, posing a serious hazard to people and property. Infestation can expand naturally and rapidly at a rate of 1–2 miles per year. Learning to identify ash trees and the symptoms of EAB damage are vital first steps to understand and manage a local infestation.

The State of Vermont has taken EAB very seriously since it emerged on the radar of forest managers and ecologists over a decade ago. The Vermont Urban and Community Forestry program (VUCFP) has a dedicated web page on EAB Management, which highlights the many resources available to communities like Norwich that are striving to manage this damaging insect pest. Vermont Invasives offers a similarly excellent overview of EAB and its impacts, also providing numerous resources for Vermonters. A number of Vermont communities have adopted formal plans to prepare for and manage EAB infestations; these are available here. Although the Norwich Conservation Commission (NCC) conducted preliminary roadside counts of ash trees in 2018 and 2019, in anticipation of EAB’s arrival, our town does not yet have a management plan in place. The process of creating such a plan is now fully underway.

Three basic options exist for managing EAB infestations, and most Vermont communities have adopted action plans that combine all three. Briefly, these include:

  1. Stem inoculation of ash trees that are considered high-value, because of their cultural, aesthetic and/or historic importance to a community or an individual landowner. Treatment must be conducted while trees are fully leafed out, between June and mid-September. See our page on Emerald Ash Borer Resources for more specific information on inoculation options.
  2. Preemptive removal of healthy ash trees that, once infected, will pose an unacceptable risk to property, infrastructure and/or public safety.
  3. Allowing trees that are neither high-value nor a risk to public property and safety to become infected and die naturally. This latter strategy typically applies to ash trees that are situated away from public spaces, residential homes, or commercial buildings.
Norwich has ash trees that likely qualify for each of these treatment options.

Inaction on managing EAB impacts is not an option for Norwich – or any community with ash trees. The documented presence of this destructive pest near our village center underscores the urgent need to develop and implement an effective action plan. Town officials, including the Tree Warden and members of NCC, are working hard to craft an immediate and effective management plan. That plan, when completed, will be adjusted and adapted in response to the progression of Norwich’s EAB infestation and new knowledge that emerges. Proactive treatment or removal will unquestionably be expensive, but reactive removal of infested ash trees and the damage they cause will entail significantly higher costs, thus the importance of developing and implementing a management plan.

EAB will affect every Norwich resident, as it proliferates and begins to kill our ash trees. We must all learn about this invasive insect, monitor our own properties for evidence of infestation, educate our neighbors, pay close attention to upcoming community initiatives for managing our ash trees and planting replacements, and be prepared to pitch in. Only a concerted, coordinated management plan and town-wide effort will avert the worst disruption and expense that EAB is poised to inflict on Norwich.

Photos

Click to see a larger version, with caption.