Idaho Officials Warn Public to Watch for Emerald Ash Borer as Destructive Beetle Advances Toward State
CALDWELL, Idaho — State and university officials in Idaho are urging Canyon County residents and property owners across the Treasure Valley to keep a close eye on their ash trees as the emerald ash borer — a destructive invasive beetle responsible for killing millions of trees across North America — continues its march toward Idaho’s borders. Though the pest has not yet been documented in Idaho, University of Idaho and state lands officials say monitoring and early detection are “critically important” to limiting the damage when the beetle eventually arrives.
Background: A Devastating Pest Moving West
The emerald ash borer, originally from northeastern Asia, was first detected in the United States in 2002 in the Midwest. Since then, it has spread across most of the eastern contiguous United States and southeastern Canada, reaching several Western states including Oregon and Colorado, as well as British Columbia. The beetle has decimated millions of ash trees throughout its North American range, and experts warn that “millions more ash trees in yet-uninfested areas are still at very high risk.”
UI Canyon County Extension horticulture educator Brad Stokes, based in Caldwell, and Idaho Department of Lands forest health specialist Erika Eidson, based in Coeur d’Alene, jointly issued a public announcement warning Idaho residents of the threat. “Stopping the borer’s spread is infeasible,” they wrote, “but timely proper management can slow it down.”
In Idaho, the State Department of Agriculture manages the invasive species program. While Idaho has no native ash trees, ash have been widely planted throughout urban communities — including in Nampa, Caldwell, Middleton, and across Canyon County — and provide significant ecosystem benefits. Stokes and Eidson estimate the value of ash trees statewide at tens of millions of dollars.
What Canyon County Residents Should Watch For
The emerald ash borer is notoriously difficult to detect in the early stages of infestation. Initial activity is often limited to the upper crown of a tree, making distinctive damage signs hard to spot from the ground. Residents and property owners should watch for S-shaped galleries under the bark, D-shaped exit holes in the bark, branch dieback in the upper crown, yellowing or wilting leaves, excessive sprouting near the base of the trunk, bark splitting, and unusual woodpecker activity.
As an infestation progresses, larvae feed on the tree’s vascular system and inner bark layer, cutting off the upward movement of water and essential nutrients. Ash trees that are not treated with pesticides — either preventatively or very early in an infestation — are expected to die within a few years. “Significant losses are expected when this beetle invades Idaho,” Stokes and Eidson wrote.
Moving firewood is believed to have helped spread the borer across the country, Stokes noted — a concern for Canyon County families who transport wood from other regions for campfires or home use near Lake Lowell and other outdoor recreational areas.
Impact on Canyon County and Treasure Valley Communities
Many Idaho communities have already stopped planting ash trees in parks and along streets in anticipation of an eventual infestation. However, ash trees “continue to be grown and sold by Idaho nurseries, and ash are still often planted in newer developments and on private property,” according to Stokes and Eidson — a pattern common in fast-growing areas like Canyon County’s expanding suburban neighborhoods.
When the borer does arrive, the financial burden of treatment, tree removal, and replacement “will largely fall on municipalities, HOAs and similar organizations, and private citizens with ash trees,” Eidson said. That reality makes early detection all the more valuable. “Early detection of an emerald ash borer infestation allows for a variety of different management strategies and more cost savings,” she said.
Stokes offered practical guidance for homeowners and local planners: “A great forward-thinking approach to managing this would be to be very selective about plant selection in the urban/suburban environments, including strong consideration of not planting ash.”
For broader coverage of agricultural and invasive species issues affecting Idaho communities, visit Idaho News. Canyon County residents interested in wildlife and land management may also be interested in the Idaho Department of Fish and Game’s plans to stock rainbow trout in Southwest Region ponds this season.
What Comes Next
A multi-agency steering committee is currently developing an updated statewide emerald ash borer response plan. The Idaho Department of Lands is administering the contract with the Samara Group to update that plan, with the primary goals of clarifying agency roles and responsibilities in the event of a confirmed detection and providing planning resources for community forestry programs.
Each summer, IDL places funnel traps specifically designed to detect emerald ash borers in at-risk areas across the state. The department has also launched a branch sampling program that includes instructions for arborists and a public reporting portal. UI Extension educators operate an Idaho insect identification website, and UI Extension, with support from IDL, has published a bulletin on the emerald ash borer to assist in identification and response.
Residents who suspect they have spotted signs of an emerald ash borer infestation are encouraged to submit photos and information through the UI Extension insect identification website or the IDL reporting portal to assist state officials in early detection efforts.