How to Create a Trap Tree to Monitor for Emerald Ash Borer

Introduction:

Example of properly girdled ash tree
Source: Blue Hill Heritage Trust

Emerald ash borer (EAB) is spreading within Maine (www.maine.gov/eab). One tool available to detect EAB is a girdled ash tree, often referred to as a trap tree.

To create a trap tree, an ash tree is girdled (the bark peeled off all the way around the tree) in May or early June. This will slowly kill the tree. The tree stays alive throughout the following growing season. Girdling stresses the tree, causing it to release compounds into the air which make it attractive to EAB in the area. If present, EAB are more likely to be attracted to this tree, rather than a random ash tree. Girdled trees are cut the following fall or early winter and sections are peeled. It is highly recommended that volunteers who girdle a tree participate in one of the Maine Forest Service log-peeling workshops. There, expert guidance will be available during the sampling process. 

How to Select an Ash Tree:

  • Any species of ash (Fraxinus spp.) can be used (not mountain ash).
  • Trees that have at least one side open to sunlight such as those at the edge of road, field or stream, or are above the canopy, are much more attractive to EAB and make better trap trees.
  • Tree should be healthy prior to girdling.
  • Tree stem should be 4 to 10 inches diameter at about 4.5 feet from ground level. Larger trees
  • can be used, but are harder to process.
  • Trees should be girdled between mid-May and early-June.

If you have any questions about selecting or girdling a tree, please contact the Maine Forest Service: forestinfo@maine.gov or (207) 287-2431.

How to Girdle an Ash Tree:

  • Between mid-May and early-June, peel an 8- to 10-inch section of bark from the lower stem.
    • Peel to the sapwood. At this time of year, the bark will slip away from the sapwood easily. When this happens, you know you have peeled deep enough.
    • Young, vigorous ash will sometimes callus over the girdle, this reduces the stress and the trees attractiveness to EAB. Therefore, make sure the girdle is clean, and is at least 8- to 10-inches tall all the way around the trunk. 
    • Be careful not to cut into the sapwood (see below).
  • Use a drawknife or other precision tool to perform the cuts for girdling.
    • If you cut into the sapwood, you will disrupt xylem cells that transport water. This can cause the tree to die too quickly and eliminate its attractiveness to EAB.
    • An alternative to the drawknife is a pruning saw or other tool to make two parallel cuts 8- to 10-inches apart. Then use a chisel or other tool to remove the bark between the cuts. A chainsaw is not recommended because it can be difficult to avoid damaging the sapwood.

How to Participate in the EAB monitoring Network:

If you choose to girdle an ash tree for EAB monitoring, please use this on-line form to report it to the Maine Forest Service. You can also reach out at forestinfo@maine.gov or (207) 287-2431 if you have trouble with the form. The Maine Forest Service will follow up with instructions in the fall for processing the tree. Processing involves felling the tree, cutting several sections of the trunk and peeling those to look for often subtle signs of EAB activity. Your data will help inform more efficient management of EAB.