Emerald ash borer was first confirmed in St. Paul in 2009, and since then it has spread through nearly every neighborhood in the metro. The small metallic green beetle lays eggs in ash bark, and its larvae tunnel under the bark, cutting off the flow of water and nutrients. An untreated ash usually dies within three to five years of infestation.
If you have an ash tree, you have three real choices: treat it, remove it, or remove it and replace it with something better suited to the site. The right answer depends on the health of the tree, its size and value to your property, and your budget over the next decade.
Step one: confirm it is an ash
Ash trees have opposite branching, meaning branches and buds grow directly across from each other. Their leaves are compound, with five to eleven leaflets, and mature bark has a distinctive diamond pattern. Green ash and white ash are the most common in yards and on boulevards. Mountain ash is not a true ash and is not affected by the borer.
Step two: look at the canopy
The single most useful measure is how much of the canopy has already been lost. Look at the tree in June or July when it should be fully leafed out. Compare the upper crown to the lower branches and to a healthy ash nearby if you can.
- Less than 30 percent canopy loss: treatment is usually very effective
- 30 to 50 percent loss: treatment may work but results vary, and an arborist should assess
- More than 50 percent loss: removal is usually the safer and more economical path
- Woodpecker damage, bark splits and D-shaped exit holes all indicate active infestation
What treatment involves
The most effective treatments are trunk injections applied by a licensed applicator. We drill small holes at the base of the trunk and inject a measured dose that the tree carries up into the canopy. Because the product stays inside the tree, there is no spray drift into gardens or neighboring yards.
Injections are done every two years, typically between late May and late June when the tree is moving water actively. Pricing is based on trunk diameter at breast height. As a sample figure, a 20 inch diameter ash might cost around $300 to $380 per treatment, or roughly $170 per year over time.
What removal costs
Removal of a mature ash is not cheap, and dead ash becomes more expensive to remove the longer it stands. Once an ash dies, the wood dries and becomes brittle, which makes climbing dangerous and often means a crane is needed. A large backyard ash near a house can easily cost $1,800 to $3,500 to remove, plus stump grinding and replanting.
Over twenty years, treating a healthy, valuable ash every two years often costs less than removing and replacing it, and you keep the shade, stormwater benefits and property value of a mature tree the whole time.
When replacement makes more sense
Not every ash deserves to be saved. Trees planted too close to the house, trees with poor structure, or trees under power lines may be better replaced. Removal also makes sense for trees already in decline, because treatment cannot repair tunnels that have already cut off the vascular system.
When we remove an ash, we recommend replacing it with a diverse, resilient species suited to the site. Good options for Twin Cities yards include swamp white oak, Kentucky coffeetree, hackberry, disease-resistant elm cultivars, and serviceberry for smaller spaces. Planting a mix of species protects neighborhoods from the next pest the way ash monocultures could not.
Do not wait too long
The biggest mistake we see is waiting. A tree that could have been treated for a few hundred dollars three summers ago becomes a brittle, hazardous removal. If you are unsure, book an assessment. Our plant health care specialists can tell you in a single visit whether treatment is likely to work, and the assessment fee is credited if you book treatment or removal with us.
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