Trap Trees: A Detection Tool for Emerald Ash Borer

Ash trees being girdled as a detection tool for emerald ash borer (EAB).  Photo: ME Dept. Ag.

Girdled ash trees are an effective detection tool for emerald ash borer. Emerald ash borer adults are attracted to stressed ash trees, and lay more eggs on stressed than healthy trees. Girdling ash by removing the bark and phloem around the entire circumference of the trunk, creates an effective attractant for the insect.

Girdled trees are allowed to stand for a growing season, and then are removed for processing. Processing involves removing all of the bark on specific sections of the trunk to search out larval feeding galleries and emerald ash borer life stages. Although girdling and bark peeling are labor intensive and involve the sacrifice of a live tree, girdled trap trees are a good option for detection of EAB, and may be one of the best options for concerned landowners (but see also biosurveillance).

A girdled tree will not attract EAB onto your property. It can only draw EAB in from about 100 yards. If EAB is close enough to be attracted to your girdled tree, it is almost certainly already on your property at levels too low to be detected. In fact, a girdled tree is likely to protect other ash on your property, since it will act as a sink, drawing EAB away from your other trees. Girdled trees can be used as part of a management strategy in the early years of an infestation, to prolong the life of surrounding ash trees.

How to Girdle a Trap Tree for Emerald Ash Borer Detection

In spring, an ash tree is ‘girdled’ (the bark peeled off all the way around the tree). Although this will eventually kill the tree, it stays alive throughout the following year. Girdling stresses the tree, causing it to release compounds into the air which make it attractive to local emerald ash borer (EAB). If there are any EAB present, they will be attracted to this tree, rather than flying to random ash trees. (This also helps protect nearby ash trees.) EAB will lay their eggs in this tree, and the larvae will start to tunnel beneath the bark. During the fall or winter the girdled trees are cut and sections are brought to a Maine Forest Service log-peeling workshop where the bark is stripped from the sections to look for signs of EAB tunneling. Log peeling workshops are held throughout the state.

Selecting a Trap Tree:

  • Any species of ash can be used (not mountain ash).
  • Trees that have at least one side open to sunlight (edge of road, field or stream or are above the canopy) are much more attractive to EAB and make better trap trees.
  • Trees should be 4-10 inches DBH (larger is acceptable, but is more work to fell).
  • Trees should be girdled between late May and early June)
  • If you have any questions about selecting or girdling a tree,
    please call Colleen Teerling at 287-3096

How to Girdle Trap Trees:

Using a drawknife, peel the bark away from the tree down to the sapwood. In the spring, the bark will slip away from the sapwood easily. The girdled area should be at least 8-10 inches long, but you may peel the bark away all the way to the ground.

Be sure to get all the way down to the sapwood. Young, vigorous ash trees will sometimes begin to callus over the girdle during the summer. This reduces the level of stress and presumably makes the tree less attractive to EAB. To reduce the chance of this, try to remove all phloem tissue

Alternately you may use a pruning saw, chainsaw or other tool and make two parallel cuts, about 10-12 inches apart. Each cut should completely encircle the trunk. Cut through the phloem and down to the wood on each cut. Then use your drawknife, saw or chisel to remove the bark and phloem in the space between the two cuts. Be very careful not to cut into the sapwood. If you cut into the sapwood, you will disrupt xylem cells that transport water. This can cause the trap tree to die and be ineffective as a trap. For this reason, we recommend girdling with a draw knife rather than a chainsaw.

If you wish to girdle a tree for EAB detection, please contact us.

If you have any questions please contact: colleen.teerling@maine.gov