Delimitation of Emerald Ash Borer Starts Nov. 4 in Boulder

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In late September, the emerald ash borer (EAB), an invasive pest of ash trees was identified within the city limits of Boulder. Since that time, staff from the City of Boulder Forestry Division and the Colorado Department of Agriculture (CDA) have worked cooperatively to complete a visual assessment of all public and private ash trees within a half mile of the initial infestation.

Staff visually assessed hundreds of ash trees from the ground, looking for symptoms of infestation, which include large branch dieback in the tree crown, woodpecker damage and excessive sprouting. Fortunately, no obviously symptomatic ash trees were discovered outside of the initial cluster of infested trees, however; EAB is very difficult to detect in early stages.  To determine the full extent of infestation, a delimitation survey begins this week. The survey is being conducted by staff from city forestry, CDA, Colorado State University Extension, and forestry staff from other Front Range cities who have graciously offered to assist. It is anticipated to take up to six weeks to complete.

For the delimitation survey, the city has been divided into plots or grids of one-square mile each. Crews will remove two small branches from each of 10 ash trees near the center of each plot. The branch samples will be peeled and examined closely for the presence of emerald ash borer life stages. The branch sampling protocols were developed by the Canadian Forest Service (CFS). The CFS found by performing random branch sampling on asymptomatic trees with this technique, they were able to detect EAB several miles away from the original location before trees become symptomatic. The goal is to determine the full extent of infestation within the city limits.  The results of the survey will also help guide the future city of Boulder EAB Response Plan to manage the infestation within the city and potentially slow the spread to nearby communities.

On Tuesday, Nov. 5, the city of Boulder  hosted an EAB “tree dissection” for forestry staff from other Front Range cities and Wyoming. Staff from CSU Extension, Colorado Department of Agriculture and U.S. Department of Agriculture, Animal Plant Health Inspection Service, Plant Protection and Quarantine (USDA APHIS PPQ) were on hand to teach other forestry professionals what EAB looks like and to demonstrate branch peeling techniques to find EAB larvae. More dissections are planned to educate tree care companies.

There are approximately 38,000 city park and public street rights-of-way trees under the jurisdiction of the Boulder Parks and Recreation Urban Forestry Division; approximately 6,000 are ash trees (15 percent of the public tree population).

For more information, please contact the City of Boulder Parks and Recreation Department’s Forestry Division at 303-413-7245.

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