The Homeowners Column

The Homeowners Column

Emerald Ash Borer on the horizon

Photo of Sandra Mason

Sandra Mason
State Master Gardener Coordinator

Why does it require a tragedy to give us perspective? Just as I am going through the four stages of Japanese beetle grief: hope (that they won't be too bad this year); denial (there are just a few); anger (I can't believe how many there are on my roses) and resignation (oh well, they will be gone in a few weeks) we get a report of emerald ash borer (EAB) in Bloomington.

Earlier this dreaded exotic pest had been found just in northern Illinois. In other states unfortunately it has killed millions of ash trees in Michigan, Indiana, Ohio, Maryland, and Ontario Canada. It brings a whole new meaning to the phrase a "pile of ashes".

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.

Considering the devastation this pest can cause the Illinois Department of Agriculture is not sitting idle waiting to kiss ashes goodbye. IDNR, in cooperation with the USDA Animal and Plant Health Inspection Service (APHIS), set out 3700 purple box kite looking traps to determine if EAB is already in other areas of Illinois. The beetles in Bloomington were found thanks to one of these purple traps.

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 use only locally acquired firewood.

At present EAB attacks only ash trees (Fraxinus spp.). If you have an ailing tree make sure the tree is really an ash. Ashes have compound leaves. Their leaves are composed of 5-9 (usually 7) leaflets along a main rib. Leaves are attached opposite each other on the stem. We have mainly green and white ash, but we also find European, black, and blue ash. Mountain Ash is a completely different beast, so it is not affected.

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. Pesticide treatments of imidacloprid and other professionally available pesticides are showing promise for tree protection and treatment. So if you have an ash tree is it best to treat it with a pesticide? UI Extension entomologist Phil Nixon offers these tips:

  • Preventatively treat ash trees no more than 15 miles from known infestations.
  • 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.

Suddenly Japanese beetles don't seem so bad.

If you suspect a tree has EAB, contact your local county U of I Extension office.

For more information check out and or stop by our office for fact sheets.

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