The articles below are a series printed in Maine Woodlands, the 20 page monthly publication of 
Maine Woodland Owners.

Emerald Ash Borer Now Found in Maine

 By Tom Doak, Executive Director

(Article originally printed in the July 2018 edition of Maine Woodlands).

      Emerald ash borer (EAB) has arrived, according to the Maine Forest Service. This non-native insect is a huge threat to all true ashtrees  (Fraxinus spp.) – white, green and black (often called brown) in Maine. It does not affect other tree species, including mountain ash (Sorbus spp.)

     It is not a surprise that EAB was found in Maine, but the location was – Madawaska, in the far north. Most people assumed it would be discovered first in southern Maine, given its recent spread through much of New England, and presence along the New Hampshire border. It’s likely that EAB exists in other places in Maine that have not yet been discovered. 

     First detected in Michigan in 2002, EAB has spread rapidly to 34 states and four Canadian provinces. The insect – native to China, eastern Russia, Japan, and Korea – probably arrived in shipping material sometime in the mid 1990s. 

What does this mean for woodland owners? 

     Emerald ash borer has caused widespread mortality wherever it’s been found. Once infected, a tree will die in three to five years. There is no effective treatment. It is a mobile insect, and widespread cutting and destroying of affected trees have proven fruitless. Spraying does not work.  It has no natural enemies to help keep the population in check. Cold will not limit its spread, since it occurs naturally in cold climates. 

     One big question is how quickly EAB will spread. The insect is a good flier and movement of infected wood increases its distribution. A federal quarantine will be imposed – likely on a county basis regulating the flow of wood from Aroostook County – in an effort to slow its spread.

What should you do?      
     Like a lot of things in nature, there is no simple answer. What seems pretty certain is that EAB will spread, and where it is found there will be significant mortality of ash. In states with full infestations, some trees have survived. Genetic diversity, particularly within white ash, may play a role.  But the long-term prospects of ash trees in the forest are not good. What to do as a woodland owner  depends a lot upon how close you are to a known infestation, how many ash trees you have, how valuable or large the ash trees are, and how concerned you are with the potential loss of the trees.

     First, do not panic or overreact. EAB is absolutely a serious pest. But outbreaks will likely occur as concentrated areas, initially. It could be years before it’s found near your property.   

     Conventional wisdom says that if you are within 10 miles of a known infestation, you should take action if you want to salvage the value of ash trees. Currently, the only known infestations within 10 miles of areas of Maine are the recently discovered site in Madawaska, and land in the southern counties of New Hampshire just within 10 miles of York County. Certainly if you have a significant volume of ash trees within 10 miles of an infestation, or are planning a harvest soon, removal of the more valuable ash trees is worth considering.

     Woodland beyond 10 miles of an infestation has a lower risk. In anticipation of the eventual spread of emerald ash borer, Maine Woodland Owners have intentionally favored other tree species over ash on lands owned and managed through our Land Trust program. We have removed mature ash trees as part of scheduled timber harvests, while leaving high-quality but smaller ash trees – those not large enough to be sold as sawtimber. The idea has been to limit the loss of high-value trees, while accepting the risk of the potential loss of smaller trees if an infestation of EAB should occur.

     This approach assumes we would be unlikely to return to those harvest sites again for another 15-20 years. Where we expect to return in just a few years, or on easily accessed sites, we leave more ash.  In the past, managing for ash would have been a long-term priority; now we see the long-term potential of ash as very uncertain.

The Maine Forest Service offers this advice:

“If you’re growing trees for timber income, don’t cut immature ash too early. If the trees are too small to yield high value sawlogs, you may get a better return if you allow them to grow. They will increase in volume, and may improve in grade, which will lead to a better financial return. If the trees are attacked by EAB, harvest quickly for highest quality veneer and sawtimber. Once EAB feeding causes 50% crown dieback the high-value sapwood can be discolored.

     If you decide to cut, consider leaving scattered and small diameter ash trees in the woods. Ash left behind may help slow dispersal of EAB [they may remain in that location longer], help manage spread, and provide genetic diversity in case of tolerance of or resistance to EAB. The last trees standing will be the last to produce seed.”

     We will have an ongoing newsletter series on emerald ash borer, including updates on any quarantine provisions imposed on landowners, any new infestation findings, and an analysis of the latest forest inventory data showing where the greatest concentration of ash exists in Maine. 

Tom Doak

Executive Director

More information about emerald ash borer is available at:

Q and A on EAB
By Tom Doak, Executive Director 
(Article originally printed in the August 2018 edition of 
Maine Woodlands).


As I mentioned last month, emerald ash borer (EAB) has been found for the first time in Maine.  This highly destructive insect attacks all true ash species – white, brown (also called black) and green. This nonnative insect has devastated ash trees in the United States since it was first detected in Michigan in 2002.  To date, it’s been found only in far northern Maine, in Madawaska, though most experts believe there are other, undetected, sites elsewhere.  

The Maine Forest Service (MFS) has indicated it is likely to issue a “stop movement” order for wood in the area of the infestation, to be followed by a quarantine regulating the flow of ash trees, though neither has been finalized as I write. MFS has deployed additional EAB traps in northern Maine as a result of the initial detection.
In response to last month’s article, we received some questions from members. One was “What will happen to the insect if EAB kills all the ash trees?” Once an area is infected, EAB will likely kill a high percentage of the ash trees, but not all. There will be some resistance. So a low level of insect population is likely to remain, even in heavily affected areas. And since the insect is mobile, once the ash population is reduced the insect is likely to disperse to other areas in search of trees. 

A second question was, given that EAB is native to Asia, are there any ash trees left there? Yes, there are. Emerald ash borer, and insects and diseases that affect EAB, evolved together. There are natural checks in EAB’s native areas, just as there are natural checks on insect species native to Maine. The problem with a non-native insect like EAB is that there are no natural enemies present. It may be possible to introduce predators, but even if that’s done, it can take a very long time to build up to levels high enough to limit the EAB population.

We will provide regular updates on emerald ash borer in our newsletter and on the website. Next month, we’ll describe the importance of ash trees to the Maine forest and economy.


Links to Maine Forest Service Information Sheets on Emerald Ash Borer (EAB):

Information Sheet # 28 - Emerald Ash Borer, Information for Landowners
Information Sheet #29 - Guidance for Maine Forest Managers