Emerald Ash Borer in Naperville - get ready to do battle!

The Emerald Ash Borer (EAB) made its unpleasant debut in southwest Naperville in 2008, and in the ensuing three years, has spread to many subdivisions in town.  Many of us have ash trees gracing our parkways or properties and we are rightly concerned about keeping them.  Should we treat our trees, leave them alone, or remove them?

The EAB is such a threat because of its life cycle.  It is a small, 5/8” greenish insect that feeds on the leaves of the ash tree, and then lays eggs in the bark.  The main damage is done by the larvae which hatch and tunnel around under the bark, effectively girdling the tree.  Symptoms do not show up until significant damage to the tree has occurred.  On top of that, since the insect has been confirmed in the near vicinity, it is very likely that most of our trees already are harboring the pest.  The best chance of saving our trees is early treatment, before the insect larvae multiply enough to cause irreparable damage.

Symptoms of infestation include yellowing and thinning of the foliage, excessive sprouting from the base of the trunk, vertical bark splitting, evidence of enthusiastic woodpeckers, and on closer inspection, 1/8” diameter D-shaped exit holes in the tree trunk.

The homeowner must weigh the value of the tree in regards to shade, beauty and emotional value.  Removal is not recommended unless the upper branches show at least 40% dieback; at this point the tree will not recover from the infestation even with the help of insecticides. Taking down a large tree and its stump might run $1000 or more plus the cost of a replacement. 

There are insecticides that have demonstrated effectiveness against the EAB.  These consist of soil injections or drenches, trunk injections, and bark/foliar sprays.  They are either systemic, which kills the larvae inside the tree, or external, which kills the leaf feeding insects. 

Small trees up to about 10” in diameter can be treated by the homeowner, typically with Bayer Advanced Tree & Shrub Insect Control.  It is available at hardware and home improvement stores.  The directions must be followed precisely; more is not better.  A mid-April application gives the best chance of control.  However, most of our parkway trees are much larger than 10” in diameter.  Treating them will require a professional’s help and can run $200-300 per tree per year.  Treatment is a long term commitment, or at least until a nearby replacement tree grows large enough or a “cure” is found.

Unfortunately there are not any feasible organic options at this time, but ongoing research suggests parasitic wasps may be of future help in controlling the insects.  Since the EAB is non-native, it does not have significant natural predators built into the local ecosystem yet.  It is always helpful to reduce stress on the tree, so keeping our trees well watered in the heat of summer is a good idea.  Whatever fertilizer is used on the surrounding lawn is sufficient for the tree as well.

If professional help is sought, always use a certified arborist.  They have access to the latest information and formulations of the product that work on larger trees.  There are other products available to them, such as Tree-Age (“triage”) that has shown excellent effectiveness for at least 2 years, even with very heavy insect pressure.  Sometimes different products are applied in combination or in spring and fall.

If you decide to treat your ash trees, please complete the Naperville Emerald Ash Borer Treatment Form (http://www.naperville.il.us/emplibrary/EmeraldAshBorerTreatmentForm.pdf) and return it to the Department of Public Works each time the tree is treated. If an arborist identifies an emerald ash borer infested tree anywhere on your property, please notify the Department of Public Works at (630) 420-6095.

In summary, we are not helpless against this invasive pest; we have effective treatments available to us and removal of our trees is not mandatory unless damage is irreversible.

Thanks to these certified arborists for their assistance with this article:

Joe Krupke

The Davey Tree Expert Company

630-293-9336

Steve Potter

Tree Concepts

630-768-0080

Carl Schultz

Horticultural Consultants

630-851-1898