The Emerald Ash Borer (EAB) is a wood-boring beetlewhich poses an ongoingthreat to all North American species of ash.  This insect was accidentally introduced from Asia, most likely in the 1990's, and has resulted in the deaths of millions of ash trees across North America. While the threat level varies by region, once present it rapidly kills all unprotected ash trees that it invades.

In our area, an EAB infestation was detected on the University of Colorado Boulder campus in September 2013.  In the years since, infestations have been confirmed in numerous locations along the Front Range including Erie, Broomfield and Thornton as well as Adams and Larimer counties.  In Louisville, state officials confirmed the presence of EAB in May 2020. Most recently, Littleton has detected the beetle’s presence in the summer of 2023.    

In Louisville, staff estimates the City has a total population of 123,000 trees with approximately 15% (18,000) being ash.  Out of those 18,000 approximately 1,000 are on public property with approximately 20% being classified as high value.  High value trees are identified for having substantial size, being located in parks or other prominent locations, being relatively free of insect, disease, and wounds, and possessing good physical structure.   

As a short-term management approach, staff has recommended treating high value trees with insecticide trunk injections utilizing an organic labeled product by the trade name of LALguardAZA. The cost of injection generally varies per trunk diameter and is dependent upon number of treatments and whether applied by City staff or out-sourced.

For long-term management of the urban canopy, staff suggested working proactively to diversify the species of trees within the City. Diversification increases the resilience of the overall canopy against current and future threats - which have historically impacted various individual tree species.  These ongoing efforts include discouraging the planting of new ash trees, removing existing ash (whether infected or not) and ensuring a wider variety of trees are planted as part of new public and private development projects.   

EAB will become increasingly invasive means that the situation is dynamic and information will evolve as we move forward.  Colorado State University Extension Services is the "go to" institution for extensive information on EAB as they have some of the most highly regarded entomologists in the nation advising on best management practices.

Information:

• Questions and Answers
• November 2013 Announcement
• EAB detected in Louisville (2020)

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