Coming to an Ash Tree Near You: Emerald Ash Borer in New Hampshire’s Towns and Cities

Karen Bennett

Introduction—Trees and forests are important

New Hampshire is covered in trees—84% of the land is forested—and that doesn’t include the trees on town and city streets and parks and in yards. Trees and forests shape New Hampshire, contributing clean water, beautiful scenery, autumn color, abundant wildlife, fresh air, natural and cultural heritage, not to mention our forest industry and much of our recreation.

Non-native, exotic insects cause more problems than native insects

Trees are rife with native insects and diseases, most of which cause no lasting harm because the trees evolved with them and “learned to live with them” by developing mechanisms to fend-off and recover from attack. Because of global trade, insects and disease are moved from one continent to another. Once moved to a new area, almost without fail, these non-native insects are more damaging to the local trees because the trees lack the defenses they’ve developed against the co-evolved native insects. Complicating the picture—the non-native insects don’t bring along their predators and usually thrive in the new area, unchecked by predators.

Emerald ash borer is a non-native insect that infests ash—and only ash trees

Emerald ash borer (EAB), a non-native insect, was first detected in Detroit in 2002. It was likely introduced into the port of Detroit in untreated wood-based packing material shipped from Asia in the 1990s. EAB infests and kills “true” ash (Fraxinus spp.). Mountain ash isn’t a true ash and isn’t attacked. In New Hampshire we have white, green and black (sometimes called brown) ash.

Bennett - Graph 1

EAB found in Concord in 2013

In March 2013, a sharp-eyed entomologist speeding along Rte. 93 spotted an ash tree that looked all wrong. It showed the tell-tale signs of “blonding”—the classic sign of EAB infestation (more on blonding later). Within days, samples were analyzed by the U.S. Dept. of Agriculture, Animal and Plant Health Inspection Service (USDA-APHIS) and for those of us who work with trees, things haven’t been the same since.

The arrival of EAB into New Hampshire was not unexpected. The State had been monitoring EAB’s eastward march and preparing for its arrival by pulling together a team from the N.H. Division of Forests and Lands, N.H. Dept. of Agriculture, Markets and Food, USDA-APHIS, U.S. Forest Service and UNH Cooperative Extension. This team works on monitoring, regulation, education, and outreach and uses as a one-stop-shop to disseminate information.

A word about the ash quarantine

Since that initial find, EAB has been found in 41 communities in five counties—Belknap, Hillsborough, Merrimack, Rockingham, and Strafford counties. As a federally regulated pest, county-wide quarantines were imposed to slow the spread, but they haven’t been able to stop the spread. For towns in the quarantine area, road crews should be aware they can’t move firewood outside of the quarantine, nor can they move chips with ash wood in them beyond the quarantine area. The topic of state and federal quarantines is beyond the scope if this article, but a thorough treatment is on and for the authoritative answers to specific questions, contact State Entomologist, Piera Siegert (271-2561 or

Why the big concern?

Once EAB attacks an ash tree, the infested tree, if untreated, will die within three to five years—and as far as we know, no ash tree is immune from infestation and death. However, because ash trees aren’t attacked until they’re one to two inches in diameter (at breast height), we should always have small ash trees and EAB.

Ash trees are important ecologically, economically and aesthetically. We estimate 25 million ash trees over 5-inches in diameter and another 750 million seedlings and saplings are growing in New Hampshire—six percent of the northern hardwood forest. As a forest product, ash contributes over $1 million dollars to New Hampshire's economy annually. The potential disappearance of ash means one less food source for wildlife.

In many cities and towns, ash replaced the stately elm trees lost in the 1950s and 1960s to Dutch elm disease. Ash has been planted extensively as a landscape tree in housing and commercial developments over the past 30 years or more.

Look for blonding

Because EAB larvae live just under the bark, woodpeckers search for the larvae by flecking away outer layers of bark, causing the bark to look lighter—an appearance called “blonding.” Winter and spring, before the leaves emerge, is a good time to check for blonding since it is easier to see the bark.

Infested ash crowns thin above infested portions of the trunk and major branches. Up to half the branches may die in a year, starting at the top of the tree. Most of the canopy will be dead within two years after the first symptoms of decline appear.

Use the emerald ash borer management zones to plan

Left untreated, infested ash die. However, with planning and foresight trees can be “triaged” into different categories such as treat and save; remove before death; let die and remove; and let die, remove and replace.

Though the main means of spread is by people moving EAB in firewood, bark, wood chips, and other wood products, the insect moves naturally as it expands its feeding grounds. To account for this natural spread and give towns and communities time to plan, we divided New Hampshire into zones. Knowing where your community is in relation to the infestations helps you make informed-decisions. The zones are:

  • Generally infested area: EAB is in this zone, though not necessarily in all ash trees.
  • Potential expansion area: EAB isn't known to be in the area, but the area is within 10 miles of the outer limits of the known infestation. There is a high probability EAB will spread naturally to this zone within a few years.
  • Alert area: EAB isn't known to be in the area and it is more than 10 miles from the known infestation.

Assume any ash in the “Generally Infested Area” is infested or will become infested in the near future. A tree may be infested for several years before it begins to show signs of decline, so if some ash trees in a given area are exhibiting signs of attack, assume other ash are also infested. Evaluate trees for treatment on a case by case basis, with the rule of thumb—if a tree has more than half of its crown remaining, it can likely be saved using insecticides.

Landscape trees in the “Potential Infestation Area” are far enough from any known infestations that treatments can be delayed until nearby trees begin to show signs of decline. To find lists of pesticide applicators and arborists able to give treatment advice, perform pesticide applications, and prune or remove dying trees visit

Don’t be complacent

We expect EAB to march forward into the rest of New Hampshire, especially since there is a lot of ash in the western and northern parts of the state. EAB is a stealthy tree-killer. Because the female EAB lays her eggs high up in a tree, signs of infestation aren’t immediately apparent. Trees can be infested for many years before the infestation is detected. Once the infestation is detected, not all trees are infested at the same time and typically seven years after first infestation only 10 percent of ash trees are dead. However, the next five years will see 80 percent of them die. We’ve found that this lag time between detection and tree-death builds complacency.

Once a given tree is infested, it falls apart quickly and without much notice since it dies from the top down. The late October 2017 windstorm closed roads in EAB-infested towns because the dead ash limbs fell into the roads.

A checklist for cities and towns

UNH Cooperative Extension developed a checklist to help municipalities prepare—whether the town is infested, near an infestation, or many years away. I’ve highlighted some recommendations and for the complete list go to

  • Don’t plant ash. Every ash you plant now will need to be treated or removed when EAB arrives in your town.
  • Look for EAB by driving around in late winter and look for “blonding.”
  • Determine your EAB management zone and examine the current recommendations.
  • Complete an inventory. An ideal inventory includes GPS location of each tree, diameter, and a call on whether it should be treated, removed, or left.
  • Triage trees for treatment and removal. You may be able to complete this step during your inventory work.
  • Budget considering treatment, removal, and replacement costs.
  • Help educate your townspeople since everyone will be affected when EAB arrives.
  • Hold a field training exercise for town staff as well as others who are interested.
  • Make EAB information available at town offices and the town website. See for printable factsheets.
  • Contact your UNH Cooperative Extension County Forester for help with these recommendations. Call 1-800-444-8978 to contact your local county forester….and remember to visit

Karen Bennett is the Extension Forestry Professor and Specialist with UNH Cooperative Extension. Karen can be reached by phone at 603.862.4861 or by email at