Ash Trees and Emerald Ash Borer in Montana: Where Things Stand

Has emerald ash borer been found in Montana?

Not according to the sources we checked on 11 October 2026. MSU Extension's Summer 2026 article on detecting the beetle states: "To date, the EAB has not been detected in Montana." The State of Montana Emerald Ash Borer Readiness and Response Plan, published in May 2025 by Montana DNRC, the Montana Department of Agriculture, the Montana Invasive Species Council and MSU Extension, says the same thing as of May 2025.

That status can change in a single season, so treat the date as part of the fact. The MSU article reports the beetle in eastern North Dakota and South Dakota, northern Colorado and western Oregon, and the state plan adds a 2024 confirmation in British Columbia. Asked how likely a Montana detection is, the Montana Department of Agriculture's Frank Etzler told MSU Extension: "Almost certainly. It's a matter of when, not if." Before you act on anything in this guide, check the current status with your county MSU Extension office or the Department of Agriculture.

How much ash is actually growing in our towns?

Less than in much of the state, which is good news for western Montana. The state plan says roughly 30 percent of the trees planted in Montana communities are ash, and that in 16 of 74 inventoried communities ash makes up half or more of the canopy. MSU Extension notes that ash is the most commonly planted tree in many communities east of the Continental Divide.

The same plan lists public tree inventories town by town. Missoula's inventory, taken from 2012 to 2016, counted 1,802 ash among 22,537 public trees, or 8 percent. Hamilton's 2011 inventory showed 10 percent ash and Stevensville's 2013 inventory 6 percent. Those figures cover publicly owned trees only. Yards, shelterbelts and farmsteads up and down the Bitterroot hold plenty more that nobody has counted.

Is my tree a true ash?

Only true ash, the genus Fraxinus, is at risk. MSU Extension describes true ash as having opposite, compound leaves with short-stalked leaflets whose edges may be smooth or toothed. Green ash is by far the most common one planted here.

Mountain-ash is a different plant entirely despite the name. Both the state plan and MSU Extension say plainly that mountain-ash is not a true ash and cannot be infested by emerald ash borer. It has its own problems, including the bacterial disease covered in our guide to fire blight, but this beetle is not one of them.

What does an infested ash look like?

The trouble is that it looks like a stressed ash, and Montana has many of those. The larvae feed under the bark in S-shaped tunnels that cut off water and nutrients. According to MSU Extension, the upper canopy is attacked first, and the beetle is often in a tree for up to four years before symptoms show.

The signs the Montana sources list are thinning and dieback in the crown, leafy shoots sprouting from the trunk or base, heavier than usual woodpecker activity, vertical splits in the bark, and D-shaped exit holes about an eighth of an inch wide. In large trees, MSU notes, it may take several years before those holes show up on the lower trunk. The adult is a metallic green, bullet-shaped beetle about half an inch long. Left untreated, MSU says, an infested tree usually dies within two to four years, and dead ash becomes brittle and prone to breaking.

Why do ash trees here decline if the beetle is not present?

Because ash in Montana already has a long list of ordinary problems. MSU Extension names lilac/ash borer, western ash bark beetle, cankers and other disease, drought, frost, herbicide exposure and mechanical damage from mowers and vehicles, along with past topping. The fact sheet is explicit that the dieback seen in Montana ash so far has not been linked to emerald ash borer.

So a thin crown is a reason to look closer, not a reason to assume the worst. Our guide to 8 signs a tree is dying walks through the general symptoms, and a tree health and risk assessment can usually sort a drought-stressed ash from one with borers.

What should an ash owner do right now?

The agencies' advice is short. Stop planting new ash. Diversify what you plant instead, which our list of the best trees to plant in western Montana can help with. Remove ash that are already unhealthy. Do not bring firewood in from out of state. Learn the signs and keep an eye on the tree.

None of the sources tells owners to remove a healthy ash ahead of the beetle. A sound, well-placed ash is still shading the house and is worth keeping in good condition with watering in dry spells and proper pruning, which is part of our tree services.

Should I treat my ash with insecticide now?

Not yet, according to MSU Extension. Its fact sheet says preventive chemical treatments are unnecessary until emerald ash borer is confirmed within 30 miles. The Montana Department of Agriculture's information sheet makes the same point from the other direction: systemic insecticides exist, but they should only be used on trees near known populations, to limit the effect on the environment.

If the beetle does arrive, MSU says chemical treatments can be effective when properly applied, and the state plan lists treating living trees among its response tools, alongside cutting and chipping infested trees and working with federal officials on releasing the parasitoid wasps used as biocontrol elsewhere. Any insecticide has to be used according to its label, which is the law, and restricted products need a licensed applicator.

Why does firewood matter so much?

Because it is how the beetle is expected to get here. The state plan cites research that the adults fly up to two miles looking for a host, and MSU's fact sheet puts natural spread at roughly 2 to 12 miles a year. The long jumps have come from people moving infested firewood and nursery stock. Both Montana sources call firewood carried by out-of-state visitors the most probable route into the state.

Since January 2021 Montana has had a state quarantine that prohibits bringing in untreated ash nursery stock and other untreated ash products such as logs and firewood that have not been heat treated. For details, contact the Montana Department of Agriculture, which administers it. In practical terms: buy firewood where you will burn it, tell visiting family and hunting partners to do the same, and if out-of-state wood has already arrived, the state plan asks that it be burned completely and none left behind.

Who do I call if I think I have found it?

MSU Extension asks anyone who suspects emerald ash borer, or who has collected a suspect beetle, to contact their local MSU Extension agent, the Schutter Diagnostic Lab at Montana State University, or the Montana Department of Agriculture. The Department's sheet suggests preserving a specimen in rubbing alcohol for verification. A photo of the insect and of any exit holes helps too.

If what you have is simply an ash that looks worse each year, start with an arborist. We keep track of the state's updates, and you will find related guides in our Montana Tree Guide.

Call HJ Property Care & Tree Service at (406) 215-7319 or request a tree assessment and an ISA Certified Arborist will look at the tree with you.

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