The Homeowners Column

The Homeowners Column

Traps to detect a destructive pest - Emerald Ash Borer

Photo of Sandra Mason

Sandra Mason
State Master Gardener Coordinator

What's purple and boxy, hangs in trees and is sticky all over? A wayward box kite? A Barney the dinosaur trap? Soon you may see large purple things hanging in trees near you. Although they may look unintentional, they are traps for the invasive pest emerald ash borer (EAB).

This year the Illinois Department of Agriculture (IDA) in cooperation with the USDA Animal and Plant Health Inspection Service (APHIS) and cooperating cities and park districts are again using purple sticky traps to detect this destructive pest. Although it was first found in Illinois in the northern counties, last year EAB was confirmed in Bloomington and Chenoa in Mclean County. Unfortunately EAB has already killed millions of ash trees in other states including Michigan, Indiana, Ohio, and Maryland. It brings a whole new meaning to the phrase a "pile of ashes".

The traps use manuka oil to lure the beetles to a sticky death. The traps do not bring EAB into an area that is not already infested nor do they control the pest. Traps are detection devices so management decisions can be made and hopefully EAB spread can be slowed. Traps will be hung in trees in May and left until removal after the beetle's flight season ends in August. If a trap is in your area, please leave it there and report any downed traps to your city arborist or to IDA at 800-641-3934.

You can also help by looking out for EAB. Emerald ash borer adults are indeed emerald green 3/8 to 5/8 inch long beetles. Adult beetles are more abundant in June and July but may be present into early September. The white larvae actually do the damage by feeding under the bark. Their feeding cuts off the tree's vascular system and therefore food and water. The adult beetles leave characteristic "D" shaped holes in the trunk or branches as they exit.

The beetle flies short distances but can survive for long periods and long distances as a hitchhiker in wood products such as wood packing crates from its native Asia. It probably entered into Illinois in infested firewood. As people picnic and camp this time of year remember to buy and use only locally acquired firewood. Never transport firewood long distances.

At present EAB attacks only ash trees (Fraxinus spp). However a sick ash tree may not necessarily be infested with emerald ash borer. Ash trees suffer from several other insect and disease problems including ash yellows, verticillium wilt, anthracnose, and other insect borers such as lilac/ash borer and apple tree borer. As with all trees practice good tree maintenance by applying 3-4 inches of wood chip mulch, watering during drought periods, and keeping weed trimmers and lawn mowers away from tree trunks.

Quarantines and tree removals are helping to slow the spread of EAB. Pesticides are showing promise for tree protection and treatment. The only available homeowner treatment is soil applied imidacloprid. Other trunk injected pesticides are only available through professionals. Certified arborists provide expertise in properly treating EAB. Check out for a listing of certified arborists in your area. Before treating an ash tree for EAB consider:

  • The only certain method to control EAB is to remove the tree.
  • Healthy trees will survive attack longer than those in poorer health.
  • Weigh the value of the tree in the landscape against the cost of treatment.
  • Consider cost of the purchase and planting of replacement trees not susceptible to emerald ash borer.
  • Insecticidal control is more effective on smaller trees, those with a trunk diameter of less than ten inches.

If you suspect a tree has EAB, contact your local county UI Extension or the EAB hotline at 1-800-641-3934. For more info and or stop by our office.

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