Following the discovery of the emerald ash borer (EAB) in Carbondale in mid-June, the Tree Board has hosted two meetings on the topic. Early on, Town Arborist Carl Meinecke estimated that there were around 400 public ash trees in Carbondale, roughly 10% of all the Town’s trees. Between the right-of-way and HOA, River Valley Ranch (RVR) has an especially high concentration, with around 500 trees. There are an unknown number of ash trees on private property and county lands.
Unlike in the eastern United States, where native ash woodlands have been devastated by EAB, all ash trees in our region were planted here and are therefore living under controlled conditions. The first infected trees confirmed in Carbondale, also the first on the Western Slope of Colorado, were located in front of the Post Office, across from the Forest Service, and removed on June 19.
As soon as EAB was identified in Carbondale, Meinecke initiated a regional group involving other town arborists, tree companies and the Colorado State Forest Service to share resources and establish ways of slowing its spread. Moving firewood is a common way for EAB to travel, so ash wood is to be chipped or incinerated on-site. South Canyon and Pitkin County landfills were designated as disposal points.
EAB, Agrilus planipennis, is a jewel beetle native to north-eastern Asia. First discovered stateside in Michigan in 2002, the beetle has no natural predator in North America and has killed hundreds of millions of ash trees. An infected tree will die within two to four years, and the beetle can travel up to 30 miles.
On July 20, a widely-publicized Tree Board meeting invited the public and other town boards and commissions to learn more about the infestation and strategize responses. Meinecke emphasized that a plan of action should reflect the community’s values. The options are limited, however, between different methods of insecticide.
The most popular method is to pressure inject a tree with chemicals. This has shown to be effective for up to three years in protecting the tree. However, applications must be repeated indefinitely to keep the tree alive. Melissa Schreiner, a CSU Extension entomologist, stated during the July 20 meeting that studies have been done that show this method is the least harmful to pollinators.
Another method is to drench the soil around the tree’s trunk with an insecticide. This offers one calendar year of protection, however these chemicals are associated with bee colony collapse and can leach into nearby bodies of water. Spraying the tree’s bark with an insecticide offers a few months of protection with high potential for the chemical to move off target, affecting the environment.
Basalt Town Arborist Chris Beiser touched briefly on biocontrols at the meeting, stating that this is an active area of study but certainly not an option for homeowners. The risk of introducing a new species with unknown consequences should be calculated by institutions and government agencies, he said.
“If you have an ash tree you should assume that you are under threat from this insect,” advised Beiser.
To treat or to not treat…
Meinecke is now working to identify “high value ash” to protect based on factors like maturity, health, irrigation and proximity to other trees. These ash will likely receive injections to prolong their survival, while other ash trees will gradually be removed and replaced with other species.
“We can see this as an opportunity,” said Beiser. “We can use this to improve our urban tree canopy” with greater diversity and thus resilience.
Trees belonging to the genus Fraxinus are particularly susceptible to EAB. These can be identified by a diamond pattern in their grayish bark and a pointed, roundish leaf structure, with seven to nine leaflets per stalk.
Signs of EAB include the dying back of foliage and D-shaped burrow holes left by the emerging beetles. Lora Criswell with Colorado Ash, a company that offers EAB treatments, likened the holes to “half the size of a pea.” It is the tunneling of larva that causes a tree to die.
Note, Mountain ash belongs to the Sorbus species and is not at threat.
If you suspect you may have an infected tree, you should contact a local tree company or your municipal arborist. Schreiner with the CSU Extension also offered to help with verification. You can contact her at email@example.com
Find more information about EAB at csfs.colostate.edu/eab
Town-managed RVR – 278 total – 191 to treat and 87 to remove.
Town Right of Way – 129 trees – 49 to be treated, 80 to remove (many in 6-12” Diameter Class).
Town Parks – 54 ash trees – 31 will be treated, 23 will be removed.
12-18” Diameter Class – 18 trees to be removed.
A budget will be worked out to be presented to the Board of Town Trustees.