Emerald Ash Borer - What to Look For

Now is the Time to Treat

Once a tree is infected with emerald ash borer, it can take four years for symptoms to appear. This, and the fact that these ash borers generally reside in the tops of trees, makes early detection very difficult. However, knowing what to look for and what to do when you suspect emerald ash borer is present are key to saving the ash tree population.

Four Stages of Infestation

When looking for symptoms of emerald ash borer, it’s important to understand that ash trees can go through four stages of infestation. Symptoms will be different during each of these stages.

Stage 1: Early color changes in fall

The feeding emerald ash borer larvae disrupt the tree’s vascular system, creating stress on the tree. One reaction of ash trees to this stress is to enter winter dormancy earlier than normal.
Treatment for trees is still possible at this point.

Stage 2: Canopy dieback, sucker growth, and increased woodpecker activity

As the tree’s stress level increases, it may have fewer leaves in its canopy, and branch tips may be less healthy or even die back. The tree looks thin and discolored. Infested ash trees in this stage may respond to dieback by growing quick-growing sprouts, or suckers, at the base of their trunk. Also, like other insects, emerald ash borer activity tends to attract woodpeckers.
Treatment is sometimes possible at this point, but removal may be recommended.

Stage 3: Tree is visibly dead or dying

At this point, leaves – if any remain – are clearly unhealthy. The ash tree’s canopy is extremely thin, and slits in the bark are noticeable.
Treatment is no longer an option. The tree needs to be removed.

Stage 4: Completely dead ash tree

At this point, not only is the tree severely infested with emerald ash borer and a threat to other ash trees in the area, it’s a liability to the property owner. Standing dead trees are not only unsightly, they can cause hazardous conditions as the wood becomes brittle.
At this stage, the tree must be removed as soon as possible.

A Summary of Symptoms

  • Canopy dieback – Branch tips start to look unhealthy and start dying back.
  • Sucker growth – Ash trees send out sprouts at the base of their trunk.
  • Woodpecker damage – Their attracted to these insects and damage the tree in the process.
  • Bark splitting – Slits in the tree’s bark become noticeable as the tree is starved for nutrients and water.
  • S-shaped larval galleries under the bark – The serpentine-shaped galleries of emerald ash borers are easily identified. The galleries enlarge in width as the larvae grow.
  • D-shaped exit holes – When larvae mature after feeding under the bark, they emerge as adults, making d-shaped exit holes in the process.