Published on April 18, 2023
HELENA, Mont. – The City of Helena’s Open Lands Division has been working this spring to address an outbreak of Douglas Fir Beetle that has impacted trees throughout the City’s open spaces. On April 17-18, City staff attached 900 pheromone capsules to trees on the North face of Mount Helena to deter beetles from infesting new trees.
The capsules are filled with Methylcycohexenone (MCH), which is a pheromone produced by Douglas fir beetles to indicate that a tree is fully occupied, which causes beetles to continue looking for space to inhabit. Continuous searching for an unprotected tree exhausts beetle fat stores to the point of mortality, or redistributes them throughout the landscape, which helps reduce the number of attacks from Douglas-fir beetles in individual trees.
City staff noted an increase in debarked Douglas fir on Mount Helena and Mount Ascension since 2021 when Helena experienced an extremely dry and hot summer. The outbreak mirrors what is being seen throughout the Rocky Mountain West.
The Open Lands division will continue working with the Montana Department of Natural Resources and Conservation to monitor the outbreak. Trees that have died due to bark beetle infestation will be removed, starting this fall, and piled for burning.