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I have an ash tree! What now?

The distinctive leaves of ash are compound with 5-7 leaflets. Photo: Maya Williams

I have an ash tree! What now?

By Allison Pilcher
July 31, 2018

Emerald Ash Borer is an invasive beetle that has killed tens of millions of ash trees since its discovery in Michigan in 2002. EAB reached St. Lawrence County in 2017. If you have ash trees on your property, it is important to plan for EAB.

Read more about Emerald Ash Borer

Ash trees are frequently found along our streets and as shade trees in our yards. Besides aesthetic value, they clean our air, filter stormwater, reduce soil erosion and reduce energy consumption. You can calculate the approximate value of your tree using the Tree Benefits Calculator

For most landowners, the decision will be whether to treat or remove your ash tree(s). Trees in woodlots probably do not require any action. Trees near homes, power lines, and rights-of-way are regarded as high risk and should be considered for removal. Preemptive removal is also recommended for young or unhealthy trees. Highly valued trees could be good candidates for pesticide application. You'll want to consult a certified arborist when deciding whether to treat or remove a tree.


Weigh the cost of removal versus benefits the tree provides when determining whether to remove the tree. Trees that are not removed will require treatment. Preemptive removal is advised for small (less than 8 inches in diameter), low-value, and high-risk trees. Small trees do not provide much shade value, can be less expensive to remove, and replacement trees can quickly reach comparable size. It is better to remove a tree before it becomes infested, as the tree can quickly become a liability. A tree service may also charge more to remove an unhealthy tree because different techniques must be used to ensure safety when the structure of the tree is compromised. Emergency tree removal may cost even more due to the danger involved and urgent response time of the job. The cost will depend also on the size or your tree, its accessibility, and its proximity to hazards such as power lines. The take-away for removal is generally the sooner, the better.


If you choose to treat your tree, it is important to consider the financial commitment. The treatment will need to be continued until EAB has exhausted its food source in the area and moved on. Onondaga County is planning to treat a selection of its public trees (any it will not remove) through inoculation for 25 years. Treatment should begin when EAB has been confirmed within 15 miles of your property. Only one of the pesticides known to be effective against the borer, imidacloprid, is available for use by homeowners. It is usually applied as a soil drench around the base of the tree. Imidacloprid must be applied annually and seems most effective when applied in early spring.

However, if an ash tree is larger than 15 inches in diameter at breast height, homeowner formulations are not likely to be effective. It is recommended to use a certified pesticide applicator who can access the most effective treatments and determine which pesticide is most suitable for your tree (see attached list of pesticide applicators and arborists for reference). Professional treatments can be costly. When seeking a pesticide applicator, try to get two or three bids for the same type of treatment.

There are four types of pesticide application used to treat EAB: trunk injection, soil injection, soil drench, or basal trunk spray. Due to the cost benefit and effectiveness, a trunk injection of ememectin benzoate (Tree-age) is the most recommended treatment method for EAB.

Replacement Trees

It is strongly recommended that every ash tree removed be replaced by another tree. When choosing a replacement tree species, consider potential growth and site conditions. Ash are medium to large deciduous trees that typically grow in poorly drained soils. If you are replacing a number of trees, remember the 10-20-30 rule for biodiversity on your land or in your neighborhood: no more than 10% of the trees should be the same species, no more than 20% in the same genus, and no more than 30% in the same family. Some commonly recommended replacement trees for ash include bur oak, northern hackberry, black gum, sycamore, gingko, northern red oak, honeylocust (thornless), red maple, sugar maple, and common persimmon. Again, be sure to select a tree that will thrive in the conditions of the particular site.

Whether you choose to treat or remove your tree, you must plan for EAB. Being proactive is the best way to avoid more costly tree removals, keep your family and community safe, and protect yourself from liability.

Attached: PDF Certified Pesticide Applicators & Certified Arborists- St. Lawrence County

Attachment Size
Certified Pesticide Applicators.pdf95.37 KB 95.37 KB
By Allison Pilcher

St. Lawrence County Planning Office SLU PIC Intern, Summer 2018