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Emerald Ash Borer and Your Trees

Emerald ash borer (EAB), a highly destructive insect native to Asia that was introduced to the Americas in the 1900s, has made its way to Northern Colorado and to the Fort Collins area. EAB attacks both healthy and stressed ash trees, including green, white, black and blue ash, and their cultivators, killing them within two to four years after infestation. The larval stage of EAB burrow and feed under the bark of trees, cutting off the flow of water and nutrients to the tree; it’s a major threat to urban forests statewide. Ash trees have also been widely planted in Colorado neighborhoods, which makes EAB a threat to the trees in your yard.

emerald ash borer bug

According to the City of Fort Collins, city-wide, there are approximately 70,000 ash trees which make up 33% of our canopy cover in Fort Collins. The city has its own EAB response plan – they’ve already started working to cull some trees and will treat healthy ash trees – but the city’s forestry department urges property owners to start implementing their own management plans. Here’s what you can do:

  1. Find out if you have any ash trees and assess the condition of each.

emerald ash borer tree damage

Example of Emerald Ash Borer damage

  • Identifying features of ash trees include compound leaves with five to nine leaflets; leaflets, buds and branches growing directly opposite from one another; and diamond-shaped bark ridges on mature trees.
  • Know the signs and symptoms of EAB. If you see exit holes in the trunk but the canopy is healthy, then you’re most likely looking at a different boring insect. Look for a thinning canopy and epicormic sprouts on the trunk or larger branches (“D”-shaped holes in the bark and vertical bark splitting with winding “S”-shaped tunnels underneath).
  1. Monitor your ash trees throughout the year.
  2. Decide whether to have an infected ash tree treated or have it cut down.

Here’s what treatment for your ash trees would look like. There are two different treatment methods:

Soil Application

  • This treatment is applied around the base of the tree; this is done once every year.

Trunk Injection

  • This treatment is done once every two years and dependent upon other factors affecting the tree.

Trees ranging from 10-15’ in diameter could do either treatment, based on the recommendation of an arborist. Many times, an arborist will suggest getting rid of the infected tree and replacing it with something different, as there are generally factors involved with the tree other than EAB, which may cause the tree to be diseased and not survive. However, ultimately it will be up to you to make the best decision for your landscape.

Emerald ash borer is not going away. So, in order to prevent further spreading, it’s important to keep all ash material local. Don’t move any firewood or other untreated wood products out of Fort Collins; this will limit its spread to other communities. The state of Colorado has seen terrible complications from EAB and no longer recommends planting ash trees.

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