Emerald Ash Borer Confirmed for Warren County Illinois

The presence of emerald ash borer (EAB) has been confirmed for Warren County Illinois, with the initial finding coming from Kirkwood. EAB is a devastating exotic pest that attacks one of the most popular landscape trees in America, the ash tree. Unlike most native borers which only target dead or dying trees, EAB preys on healthy ash trees.

However, the presence of EAB in Warren County is not localized to Kirkwood and is more widespread than originally thought. A local Monmouth resident, Gary Fernald, notified Extension of what he suspected was EAB in Monmouth. Upon inspection, retired WIU urban forestry professor Tom Green immediately identified the small D-shaped exited holes and serpentine galleries under the bark, both indicative of EAB. In addition to the presence of EAB, there is also a startling amount of dead mature ash trees within south-west Monmouth due to this pest.

Based upon the size of the dead ash trees, retired professor Tom Green estimated EAB has been in Monmouth a minimum of four years, but likely more. Calculating with a minimum presence of four years and its annual half-mile natural spread, every ash tree in Monmouth has the potential to be infested with EAB.

How to manage EAB and its impact on your ash trees is difficult, however, in the end there are two choices: protect the tree with systemic insecticides or have your ash tree removed. Following are guidelines to assist you when weighing these two options.

Guidelines for Treatment:

According to Extension entomologist Phil Nixon, trees with up to 30-40% dieback have an excellent chance of survival with treatment, but with that much dieback the tree may not be worth keeping aesthetically.

Preserving your ash tree - If you observe more than 50% of the ash's canopy living and intact, treating with chemicals is a viable option:

  • For ash trees with less than a twenty-inch diameter at breast height (DBH) homeowners can purchase systemic treatments containing the active ingredient imidacloprid or dinotefuran. Imidacloprid is applied as a soil drench around the base of the tree and dinotefuran is applied as a bark spray. Both treatments are annual applications. Make sure to follow all label directions.
  • For trees with a DBH greater than twenty-inches, you need to hire a licensed applicator to make trunk injections of pesticides containing imidacloprid, dinotefuran, or emamectin benzoate. Imidacloprid and dinotefuran need to be applied annually, while emamectin benzoate provides two and perhaps even three years of protection.
  • How long will we need to apply treatments? Based on Michigan and Ohio who have been dealing with and studying EAB for a long time, trees will need to be protected for at least 20 years, perhaps as long as 30 years before EAB numbers drop low enough for them to die out in an area.
  • Treating your ash tree every year can be costly. Extension entomologist, Phil Nixon, recommends that homeowners can protect their trees with annual soil drenches of imidacloprid or bark sprays of dinotefuran until EAB enters the neighborhood. Then he recommends emamectin benzoate until untreated ash trees are dead and EAB numbers drop, which will be several years.

Removing your ash tree - If your ash tree has lost a majority of its canopy, contact a certified arborist to have your tree cut down. University of Illinois Extension discourages treatment of trees that have lost more than 50% of their canopy.

Warren County is within the EAB quarantine zone and moving ash wood out of this area is a violation of state regulations. (Moving firewood in general is a bad practice, so don't do it!) Ash wood can remain on the homeowner's property or disposed of at the proper location within the quarantined county. Contact your local officials for their landscape waste disposal site.

Do nothing – According to Extension entomologist, Phil Nixon, EAB poses a 98% mortality rate to ash trees. If your county is confirmed with EAB and you do nothing, the odds are obviously against you. However, a few ash, particularly white and blue ash, will survive.

A dead ash tree needs to be removed soon after death. Once deceased, ash trees degrade very quickly and run the risk of injuring bystanders and causing significant property damage as large limbs fall or the entire tree pitches over. Ensure the safety of you and others by removing an ash tree as soon as possible after its death.

With the presence of emerald ash borer in Warren County, homeowners and city officials must consider costly treatment or removal of ash trees. With all this bad news, let's shine a light on EAB as an opportunity to plan a future tree canopy filled with a diversity of species which will add value to the communities of Warren County.

University of Illinois Extension will assemble a public workshop to inform community members on their options and address homeowner questions. Once the workshop is scheduled we will post the information in the local listings or you can contact the Warren County Extension office for details.