Emerald Ash Borer identified and confirmed in Arapahoe County

What to do if you have ash trees 

Arapahoe County has identified its first case of Emerald Ash Borer, an invasive insect that infests and kills North American species of ash trees. The case was detected in a small area in northeast Littleton and was confirmed by Arapahoe County agencies, Colorado State University Extension specialists, and experts from surrounding municipalities. 

Emerald Ash Borer was first discovered in Colorado in Boulder County in 2013. Since then, the destructive wood-boring beetles have been found in Broomfield, Larimer, Erie and Thornton. Littleton has not had a confirmed case of EAB until this June. The town of Carbondale also recently reported a confirmed case discovered on June 16. 

"EAB is the most destructive insect pest in trees that we have ever seen in North America. Homeowners and HOAs with ash trees will eventually have a significant financial decision to make whether they choose to treat their ash trees with insecticides or remove them," says Lisa Mason, Horticulture Specialist and Entomologist at Colorado State University Extension in Arapahoe County. 

Emerald Ash Borer beetles target – and eventually kill – North American ash tree species including green and white varieties, and their cultivars such as "autumn purple ash," a popular white ash variety in Colorado. On average, 15% of urban trees are ash trees. 

"An unhealthy ash tree doesn't mean it has EAB,” said Mason. “Look for the distinctive D-shaped exit holes, bark splits and S-shaped tunnels called galleries underneath the bark, gradual canopy thinning and dieback, abnormal shoots of growth, smaller than normal leaves, and heavy woodpecker activity." 

Residents can take steps to protect healthy ash trees, but certain options such as insecticide treatments depend on the size and health of each tree. Since Emerald Ash Borer kills trees over a period of several years, trees that are not candidates for insecticide treatments will eventually need to be removed. Residents should follow available guidelines for properly disposing of any infested wood. 

"EAB has spread slower than expected in Colorado giving people time to make the right decision,” according to Mason. “One study showed that healthy ash trees can be treated with emamectin benzoate successfully after EAB has infested the tree as long as the tree hasn't lost more than approximately 30% of the canopy." 

Arapahoe County municipalities are currently prioritizing ash tree insecticide treatment and removal. Other services and community programs may be available to residents to help subsidize the costs of treatment or removal and to mitigate the impacts of Emerald Ash Borer on private property. 

Residents should contact their local municipality for information and resources: 

For questions about Emerald Ash Borer as well as possible diagnosis and treatment options, contact CSU Extension-Arapahoe County at MasterGardener@cztf.net or 303-730-1920. 

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