State forestry officials and University of Idaho researchers are sounding the alarm about a destructive invasive insect that could devastate ash trees across Idaho communities, including Canyon County, even though the pest has not yet been confirmed in the state.
The emerald ash borer, an invasive beetle from Asia, poses a significant threat to Idaho’s urban forest canopy, with the value of ash trees statewide estimated in the tens of millions of dollars, according to a joint announcement from the Idaho Department of Lands and UI Extension.
Brad Stokes, a horticulture educator with UI Canyon County Extension based in Caldwell, and Erika Eidson, a forest health specialist with the Idaho Department of Lands, emphasized that monitoring and early detection efforts are critically important as the beetle expands its range across North America.
Beetle’s Destructive Path Across North America
First discovered in the United States in 2002 in the Midwest, the emerald ash borer has killed millions of ash trees throughout the eastern United States and southeastern Canada. The pest has now reached several western states, including Oregon, Colorado, and British Columbia.
While Idaho does not have native ash tree species, ash trees have been planted extensively in cities and towns across the state, providing valuable ecosystem benefits to urban communities. In Canyon County and throughout the Treasure Valley, ash trees are common in residential neighborhoods, parks, and along streets.
Trees not treated with pesticides either preventatively or very early during an infestation typically die within a few years once the beetle becomes established, officials said.
Detection Challenges and Symptoms
Identifying an emerald ash borer infestation early presents challenges because initial damage often occurs in the upper tree crown, making it difficult to spot distinctive signs such as S-shaped feeding galleries beneath the bark and D-shaped exit holes.
As larvae feed on a tree’s vascular system and inner bark layer, they disrupt the movement of water and nutrients. Visible symptoms in heavily infested trees include branch dieback in the upper crown, yellowing or wilting leaves, excessive sprouting near the trunk, bark splitting, and increased woodpecker activity.
Idaho’s Monitoring and Response Efforts
The Idaho State Department of Agriculture manages the state’s invasive species program. The Idaho Department of Lands deploys funnel traps each summer in high-risk areas specifically to detect emerald ash borers.
A statewide branch sampling program has been established, complete with instructions for arborists and the public, along with a reporting portal for suspected sightings. UI Extension has published a bulletin on the emerald ash borer and operates an Idaho insect identification website to help with detection.
A multi-agency steering committee is currently developing an updated response plan through a contract with Samara Group. The plan will outline different agencies’ roles and responsibilities if the beetle is discovered and provide planning resources for community forestry programs.
Impact on Canyon County Residents
If the emerald ash borer reaches Idaho, the costs of treatments, tree removals, and replacements will largely fall on municipalities, homeowners associations, and private property owners with ash trees on their land.
Eidson noted that early detection allows for a wider variety of management strategies and greater cost savings for property owners and local governments.
Many Idaho communities have already stopped planting ash trees in public spaces to avoid future losses. However, ash trees continue to be sold by Idaho nurseries and are frequently planted in new developments and on private property.
What Comes Next
Forestry officials believe the beetle’s spread cannot be stopped entirely, but proper management can slow its advance.
Stokes recommended that property owners and landscape professionals carefully consider plant selection in urban and suburban settings, including strongly reconsidering planting ash trees. Movement of firewood has likely contributed to the beetle’s spread across the country, making local firewood sourcing an important preventive measure.
Residents who suspect they have identified emerald ash borer damage can submit photos and information through the UI Extension insect identification website or contact the Canyon County Extension office in Caldwell.