Emerald Ash Borer in Illinois: Why Dead Ash Can't Wait

The emerald ash borer is the reason for a lot of the bare, gray trees you see standing across the North Shore. It is a small, metallic-green beetle, and it has done outsized damage: over the past decade it has killed a large share of Illinois ash trees, and ash was one of the most common street and yard trees in the Chicago area. If you have an ash on your property, understanding what this pest does - and why dead ash is a problem you cannot simply ignore - is worth a few minutes.

What the beetle does

The emerald ash borer attacks ash trees specifically. Adult beetles lay eggs on the bark, and the larvae bore in and feed on the layer just under it - the tissue the tree uses to move water and nutrients from roots to canopy. As the larvae tunnel, they gradually girdle the tree from the inside, cutting off its plumbing. An infested ash typically declines over a few years and dies. There is no bringing back a tree once it is far gone; the damage is structural.

Because the beetle spread through a region full of ash with nothing to slow it down, the losses came in waves. Many North Shore parkways and yards that were lined with ash are now working through the aftermath - which is why dead ash removal has become such common work here.

Why dead ash is urgent - the brittleness problem

Plenty of trees die and stand harmlessly for years. Dead ash does not get that grace, and here is why it matters more than the average dead tree: ash wood turns brittle unusually fast once the tree dies.

A living tree, and even a freshly dead one, has wood with some flexibility - it bends before it breaks, holds a climber, and takes rigging. Within a season or two of dying, ash loses that. The wood dries and becomes snap-prone, and the consequences are exactly the ones you do not want near a house:

• Unpredictable limb drop. Brittle ash sheds branches - sometimes large ones - without warning, in wind or on a calm day. A dead ash over a driveway, deck, or sidewalk is a genuine hazard to people below.
• It becomes unclimbable. A crew cannot safely climb or normally rig a badly degraded ash, because the wood may fail under load. That pushes the removal toward a bucket or a crane - and a job that gets harder, not easier, the longer it waits.

That last point is the crux: a dead ash does not hold steady, it degrades. The tree that could have been climbed and removed cleanly this year may need a crane next year, and may start dropping limbs on its own before then.

How to tell if your ash is already gone

The signs of an ash killed or dying from the borer are fairly distinctive:

• A thinning or bare canopy, often starting at the top and working down, while other trees are in full leaf.
• Bark splitting or falling off to reveal S-shaped tunnels winding under it - the larvae's feeding galleries, and the clearest signature of the borer.
• New sprouts (suckers) shooting up low on the trunk while the upper tree is dead - the tree's last-ditch survival attempt.
• Heavy woodpecker activity, since the birds strip bark to get at the larvae.

The scratch test - checking whether the layer under the bark is green or brown - confirms how much of the tree is still alive. If most of the canopy is bare and the bark is peeling to reveal those tunnels, the tree is very likely finished.

What to do if you have a dead or dying ash

You do not necessarily need to act today, but a standing dead ash near a target should move up your list, not sit indefinitely:

• Get it assessed so you know how far gone it is and whether it can still be worked easily or is heading toward needing a crane.
• Prioritize ash over the house, driveway, and walkways, where a dropped limb has somewhere bad to land.
• Schedule before storm season where you can - a brittle ash is exactly the kind of tree a storm turns into an emergency.

The honest bottom line is that dead ash is the North Shore tree most likely to fail on its own and most likely to become a middle-of-the-night problem - and unlike most trees, waiting on it usually makes the removal harder and more expensive rather than cheaper.

If you have an ash you suspect is dead or dying - across Winnetka, Highland Park, Deerfield, Northbrook, or anywhere on the North Shore - request a free on-site estimate. A crew lead will tell you honestly how far along it is and lay out your options before it decides for you.