The Emerald Ash Borer will most likely become the single most destructive pest in Denver’s urban forest history. First discovered in Michigan it has since caused millions of Ash trees to die and billions in losses to municipalities for the treatment or removal and replacement of infested trees in 35 states. Denver is home to roughly 1.5 million Ash trees which is about 15% of the total tree population. Initial plantings of Ash trees were done to replace Elm trees throughout the city which had died from Dutch elm disease and Ash trees were also considered a good replacement tree for elms throughout the U.S. Now that this non-native pest has been introduced, that decision could be second guessed. Populations of the Emerald Ash Borer were identified in Boulder County in 2013 and the Emerald Ash Borer has since spread to Berthoud, Broomfield, Erie and Westminster. Wood quarantines had been placed on Boulder County and extended to Erie however with the spread of this pest to different municipalities, the wood quarantine was removed in 2019. There will be costs associated with any treatment for the Emerald Ash Borer though the most expensive would be to remove your untreated tree once it has died.
Elk Creek currently offers two different levels of control against this pest for your prized Ash trees. A systemic basal trunk spray will protect the tree for one growing season and will also help to control leaf curling aphids and other boring beetles. This treatment is also recommended for smaller Ash trees up to 8 inches in diameter at breast height. The second treatment option provides up to 2 years of protection and will also control other boring beetles. This systemic insecticide is injected into the tree using the Tree-Age I.V. Kit and is only recommended on trees with a diameter at breast height larger than 8”. In laboratory and field studies, this treatment provided the best control. Both treatments will also control the Lilac/Ash borer as well as the Ash Bark beetle. Elk Creek currently does not recommend a soil treatment of imidacloprid as this is the least effective treatment against this pest and it could also harm beneficial insects in the soil.
Systemic insecticides and preventative sprays will also help to control theses shade tree boring insects in our region: Clear Winged Borer, Flat Headed Borer, Bronze Birch Borer, Peach Tree Borer, Locust Borer, the Round Headed Apple Borer and the European Elm Bark Beetle, just to name a few.