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Recognizing and Treating for Emerald Ash Borers Archived Discussion Room

Fairfax County, Virginia

Recognizing and Treating for Emerald Ash Borers

The emerald ash borer (EAB) is an invasive pest that is causing a rapidly advancing tree mortality and safety issue for property owners in the county. Although EAB may not be visible yet, the pest is here and there is a very small window of opportunity for residents to treat and save their ash trees. On Wednesday, April 20 at 11 a.m. log online and speak to county urban foresters about the EAB pest and what to do to protect your trees.

Joan Allen : Good morning everyone! Thank you for joining us for Ask Fairfax. Today Rachel Griesmer-Zakhar and Joan Allen are here to answer any questions or concerns about emerald ash borer.

Anonymous User : Unfortunately, I can barely tell a maple tree from a sycamore. How can I identify ash trees on my property?

Rachel Griesmer-Zakhar : Ash trees can be a little difficult to spot but are one of the few native tree species that have an opposite branching pattern.  Maples, ash, dogwood and horsechestnuts are the only other tree species that have this branching pattern.  Ash trees also have a diamond shape pattern on their bark when they get older.  Unlike the other species they have compound leaves with 5-9 leaflets.

If you are unsure, there are publications available on our website that can help:
You can also call a tree care professional who should be able to identify your ash tree.   Lastly, you can bring a photo or branch sample to a Virginia Cooperative Extension Master Gardener plant clinic: or call  (703) 324-5369.

Anonymous User : What are the signs that a tree is being impacted by emerald ash borers?

Rachel Griesmer-Zakhar : Emerald ash borers cause several distinct signs when they infest an ash tree.  These include D-shaped exit holes, which can be difficult to spot on older trees with thick, blocky bark and S-shaped larval galleries which can be seen by peeling off the bark.  It is very unlikely to actually see the adult emerald ash borer beetle.
Symptoms are usually easier to see and this is the tree’s response to EAB attack.  Symptoms include dead branches in the top of the tree, loss of leaves or small leaves in the canopy, vertical splits on the bark and woodpecker feeding or blonding.  Woodpecker ‘blonding’ can be one of the most reliable ways to confirm that an ash tree has EAB because the outer bark will be stripped revealing the lighter bark underneath.
If you would like to see photos, please visit our website: 

Anonymous User : How widespread is EAB in Fairfax County?

Joan Allen : Emerald ash borer was confirmed in Fairfax County in 2008 and has been making itself at home here for approximately 8 years.  At this point it is safe to assume that if there is an ash tree in Fairfax County, it is infested with emerald ash borer. 

Anonymous User : Will the County treat my ash tree?

Rachel Griesmer-Zakhar : Unfortunately Fairfax County does not have the resources to treat ash trees on private property.  We suggest that you contact a tree care professional to assess your ash tree to determine if it is healthy enough for treatment. is a good website to find a certified arborist in our area.
Urban foresters like myself are more than willing to give educational presentations to community groups and give basic advice but are unable to do individual consultations.

Anonymous User : What is Fairfax County doing for ash trees?

Rachel Griesmer-Zakhar : In 2015, Fairfax County began treating ash trees on public property that were in prominent locations or were high value or historic trees including schools, parks and other county government facilities.  These trees were injected with TreeÄge, a systemic insecticide which is very effective at protecting ash trees from EAB.
We also do educational outreach to inform residents about emerald ash borer and its management, including giving presentations to homeowners associations and other community groups.

Anonymous User : I have 8 ash trees in my yard. Should I treat them?

Joan Allen :

Different factors can be considered when deciding whether to treat an ash tree for EAB; the current health of the tree, its size, and how valuable the tree is. As a rule of thumb, ash trees that have 50% or more of live canopy or live top, can be treated successfully for EAB. Urban Forest Management Division recommends that property owners with ash trees on their property consult with a ISA certified arborist to assess the condition of their trees and if it is appropriate to treat them with pesticides. Visit for a directory of ISA Certified Arborist in your area. 

For more information on EAB and treatment option visit:

For a slideshare presentation on EAB Homeowner Option:

Anonymous User : Does treatment work? Does it have to be applied every year?

Joan Allen : Studies have shown that pesticide treatments are highly successful. To increase the odds that treatment are successful, only treat trees that have 50% or more of live canopy or live top. The frequency of treating your trees depends on the material that is used. Pesticides with the active ingredient of imidacloprid must be applied yearly for it to remain effective. Currently, there is a pesticide available, Tree-?ge, that can be applied every 2-3 years. This material has to be applied by a professional and can be more expensive.

Anonymous User : If I take down my ash trees, what should I plant in their place?

Joan Allen :

Urban Forest Management Division recommends that homeowners plant a variety of native trees on their property. For a list of native trees visit: page 69-78 (table 12.17)
For a Slideshare Presentation on EAB Ash Tree Removal and Replacement:

Anonymous User : Will the emerald ash borer kill all of the ash trees?

Joan Allen :

EAB has killed millions of ash trees across the country. There have been many efforts to decrease its impact through restriction of movement of ash materials, pesticide treatments of individual trees, and research of potential parasitoids or predators that would prey on EAB. I think EAB has the potential to kill all ash trees but because of the efforts that many of us can make, I do not think that will be the likely outcome.
For more information on what you can do to help ash trees visit:

Anonymous User : Are other trees affected by the emerald ash borer?

Joan Allen : EAB only infests ash trees. There was an isolated documented case where an EAB larva was found in a white-fringe tree in southern Ohio. There have been no other documented cases of EAB infesting white-fringe trees or any other species of trees since then.

Adele G. Sugay : Why are ash trees so important to the local ecosystem? Do emerald ash borers ever hurt other native species of tree? If so, which ones?

Rachel Griesmer-Zakhar : The majority of ash trees in Fairfax County grow in wet areas or swamps.  These species are adapted to flooded conditions and can help regulate stormwater by reducing flooding and improving water quality by filtering water coming into streams.  When ash trees die, the benefits they provide to wet areas like streams are lost and can cause an increase in local flooding and bank erosion.

Anonymous User : Is there an ash cultivar resistant to EAB infestation? If we do not plant more ash as part of restoration activities because of the threat of EAB, is it a self fulfilling prophecy that ash trees will disappear from our landscape? Is the situation that dire?

Rachel Griesmer-Zakhar : There have been several studies looking at the resistance of native ash trees to emerald ash borer.  By and large, our native species are extremely susceptible and will die.  However, blue ash (Fraxinus quadrangulata) has been shown to be slightly more resistant than both white and green ash (F. americana, F. pennsylvanica) which are the two species primarily found in Fairfax County.

Exotic species of ash including Manchurian ash (Fraxinus mandshurica) from Asia are resistant to EAB since they come from the same region.  However, we don't encourage planting exotic species.

Al Sofila : Why are emerald ash borers so hard to eradicate? What are the best techniques to use on "infected" trees?

Joan Allen : There have been many unsuccessful eradication programs for EAB, including in Virginia. Unfortunately, they have been unsuccessful because it is very difficult to identify newly infested ash trees. An ash tree can be infested for 2-3 years before it shows signs that it is infested. By then, EAB could have spread to too wide of an area for an effective eradication program.

Anonymous User : Will invasive species take over when the ash trees die since deer are eating all of our native plant species, and most young native trees can not grow beyond the deer browse?

Joan Allen : Invasive species and white-tailed deer are some of the biggest natural resource problems facing this area. EAB killing many of our native ash definitely does not make things easier on our natural world. It is possible for invasive plants to take over an area where ash trees once were but there are programs within Fairfax County that are trying to address these problems. The Park Authority has a volunteer program where residents can help remove invasive plants from county parkland called IMA. For more information visit:

There is also an active deer management program where volunteer archers help cull deer from county property as well as provide information for private property owners on how to deter deer from their property. For more information visit:

Anonymous User : Will EABs attack trees other than ash if ash trees are not in the area? Or in the future should ash trees become rare due to EAB? Are there certain other tree species we should monitor for EAB?

Rachel Griesmer-Zakhar :

Emerald ash borers are very specific in the hosts (trees) that they attack.  White fringetree which is the only other species that has been observed with EAB damage is very closely related to ash.  Other species that are closely related include Forsythia, Privet and Olive.  However, in the early days of EAB, studies were conducted on which species emerald ash borer would attack and it almost exclusively will choose ash.
It is very likely that ash trees will become rare because there is no apparent resistance of native ash species other than blue ash which is already uncommon.

Anonymous User : What percentage of dieback indicates a tree that is not worth treating?

Rachel Griesmer-Zakhar : Dieback refers to the amount of dead branches in the top of an ash tree.  When a certain percentage of the tree branches are dead, it can no longer effectively take up water and nutrients.
The insectides available work with the tree to move the chemical through its tissues in the wood up to the branches and leaves.  When an ash tree has more than 30-50 percent dead branches in the canopy, treatment is not effective.

Tent worm nests : We have tent worm nests in tree behind my home, in Devonshire Park area, as usual. Do you spray for tent worm infestations in Devonshire Park? I usually try to get rid of them in the area, by myself, but need help. Can you spray your area, so to help nearby homes? tHKS

Joan Allen : Eastern tent caterpillar is a common native insect in this area. This time of year it is very common to see the caterpillars "webby tents" in trees like cherries, apple, and plum. While the caterpillars can potentially feed and defoliate or eat all the leaves off a tree they do not ultimately harm the tree. Since tent caterpillars are an important native insect the county does not treat for eastern tent caterpillar and encourages property owners to leave them be.

Lyman T. Riadispar : I know you both work with more pests than just emerald ash borers. What is/are your favorite pest(s) and why?

Rachel Griesmer-Zakhar : What a great question!

Joan says that there are just too many and she can't choose one.

Rachel likes cicadas, which can be considered a pest to some, but she thinks they are cool insects that have a fascinating ecology.

Joan Allen : Thank you everyone for your thoughtful questions.  We enjoyed chatting with you today. For more information regarding emerald ash borer and other forest pest visit: