Turning a failing elm tree into a beetle trap

A Belgian elm tree on Boston Common near Brewer Fountain Plaza and Park Street Station has been confirmed – via inspection and with a lab sample – to have Dutch elm disease.

What is that ring around the tree’s trunk? Under the direction of our consulting arborist, Norm Helie, and City of Boston Tree Warden, Greg Mosman, the tree has been girdled. Girdling is a process where portions of the bark on the trunk of the tree are removed to expose the layer underneath. This practice creates further stress to the ailing tree, which puts out the scent of decomposition, signaling that stress and attracting the disease-carrying elm bark beetles. This clever strategy in effect makes the tree a beetle trap for a number of months. The girdled elm tree will be removed this winter, and all those beetles that were attracted to the tree will be destroyed in the process.The Friends has utilized this practice of girdling in the past as a way to further reduce the beetle population.

What about the other areas on the trunk where bark is missing? When a tree is inspected for Dutch elm disease, selected spots in the bark are opened up to create windows to allow for Norm to search for evidence of the disease. As the disease moves down the trunk, the presence of chocolate-brown streaks of fungus in the wood confirms the tree is beyond saving.

This work is an integral part of the care the Friends carries out for almost 700 trees on the Boston Common, approximately 250 of which are elm trees.