Colorado State Forest Service: Trees in burn areas more susceptible to bark beetles

Although recent wildfires in Larimer County have destroyed numerous host trees harboring mountain pine beetle populations, many unburned, dead or dying trees remain and still harbor mature beetles. When these beetles fly in search of healthy new host trees – the annual flights usually begin in early July – they will find stressed trees scorched by the fire and now more susceptible to infestation.

“Preventive treatments for surviving trees may be more important than ever right now and over the next few seasons, because in fire-impacted areas these trees represent a smaller selection of hosts and have likely experienced additional stressors,” said Sky Stephens, forest entomologist for the Colorado State Forest Service.

Stephens also said that in burned areas, high-value trees already treated this year with protective chemical or pheromone agents may no longer be safe from a beetle attack. Chemical sprays and pheromones exposed to high heat or directly to fire may have lost some, if not all, of their effectiveness.

“We are not aware of any studies that have looked at the impacts of heat, smoke or fire on chemical preventive products for mountain pine beetles,” Stephens said. “But most chemicals degrade faster when exposed to heat.”

Re-application of treatments may be necessary for living trees with scorched bark. And although any trees that have no current signs of beetle activity are suitable for application of a preventive product, Stephens warns that preventive chemical sprays may adhere less effectively to charred bark. Pheromone packets, which can be attached to trees, may be a better option in these cases.

“The window of opportunity to apply or reapply preventive products this summer is rapidly closing,” Stephens warns. “And no products are currently proven effective to save trees already impacted by mountain pine beetles.”

Landowners with specific questions about preventive treatments can contact Stephens at 970-491-6303.