Emerald Ash Borer Watch: What Boise Homeowners With Ash Trees Should Be Doing Now
We get some version of this question almost every week now: "Is emerald ash borer in Boise yet?" As of this writing, it hasn't been confirmed in Idaho, but it's already established in Colorado and has reached parts of the West Coast through Oregon, and University of Idaho Extension has been encouraging property owners to start monitoring their ash trees before symptoms show up rather than after.
Why ash trees specifically matter so much here
Green ash and white ash were planted heavily as street and yard trees across Boise from the 1970s through the 2000s, in part because they're fast-growing and tolerate our alkaline valley soils well. That means a lot of neighborhoods - West Boise (83704) and Southeast Boise (83706) in particular - have blocks where ash makes up a large share of the mature canopy. If emerald ash borer does establish here the way it has elsewhere, losing an ash tree isn't a one-off - it can mean losing shade across an entire street within a few seasons.
What to actually check on your own tree
- Thinning canopy or dieback starting at the top of the tree and working down
- D-shaped exit holes in the bark, roughly 1/8 inch across
- Vertical bark splits exposing S-shaped larval tunnels (galleries) underneath
- Increased woodpecker activity/damage on the trunk and upper branches (woodpeckers feed on the larvae)
- Sprouting ("epicormic") growth low on the trunk or at the base, a stress response
None of these signs on their own confirm emerald ash borer specifically - fire blight, general drought stress, and ordinary aging cause some overlapping symptoms in Boise's older ash, elm, and pear plantings. That's exactly why an on-site look from someone who sees this across dozens of Boise yards a year is worth it before you decide anything. Our arborist consultation service is built for exactly this kind of "is this a real problem or not" assessment, with no pressure toward removal if the tree can be treated or simply monitored instead.
If a tree is already too far gone
A badly declining or structurally compromised ash tree, especially one near a house, driveway, or power line, is a different conversation than early monitoring. Dead and heavily declining trees get more dangerous to leave standing over time, not less - see our dead and diseased tree removal page for why we treat that kind of removal differently from routine tree work.
Bottom line for this fall: if you've got a mature ash tree and haven't had it looked at in the last couple of years, that's a reasonable thing to put on the calendar now, before any problem (borer-related or otherwise) has a chance to get ahead of you.