The Emerald ash borer (commonly known as EAB) is an invasive insect that has killed millions of ash trees throughout the eastern half of the U.S. and southeastern Canada. It has been discovered in most cities and is presumed to be in all cities in Anoka County. Every non-treated ash tree in the county will likely be infested soon. It can take several years for an ash tree to show symptoms from the emerald ash borer, so even a tree that appears healthy may be in the early stages of being infested.

Emerald Ash Borer Image

How to identify an Ash tree

There are several varieties of ash trees in Anoka County – green, white, and black. Look for the following characteristics to determine if your tree is an ash tree:

  • BRANCHES-Grow directly opposite one another.
  • LEAVES-Opposite on the stem, compound, or multiple leaves on one stalk joined to a branch. Commonly have 5 to 9 leaflets.
  • BARK-Mature ash trees have a diamond-shaped, ridged pattern and appear gray in color.
  • SEEDS-Flat, winged, one-seeded samara that are oar-shaped. Seeds typically hang in clusters.
Ash Tree Bark Image
Ash Tree Leaf Image
Ash Tree Seeds Image

Signs of EAB infestation

The following signs may indicate that an ash tree is infested with emerald ash borer:

  • CANOPY DIEBACK: Leaves on the top or one part of the tree will start dying, eventually impacting the rest of the tree.
  • SHOOTS GROWING FROM TREE BASE: Sprouts growing from the roots or base of the tree indicate that it is stressed.
  • INCREASED WOODPECKER ACTIVITY: Woodpeckers feed on larvae within the tree’s bark.
  • BLONDING ON THE TREE BARK: Caused by woodpeckers stripping the bark when going after emerald ash borer larvae, the blonding appearance can be a patch or encompass nearly the entire tree.
  • CRACKS IN THE BARK: Larvae tunneling beneath the bark can cause the bark to split open.
  • WINDING PATTERNS: Winding serpentine patterns underneath bark and D-shaped exit holes: Larvae feeding on the tree’s tissue leaves a serpentine pattern underneath the outer bark, and adult beetles leaving the tree create D-shaped holes.

If you think you have an infested ash tree, contact your city forester or parks department to determine your next steps.

E A B Infested Tree
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Managing Ash Trees

There are two options for managing ash trees on your property: preserve them by using an insecticide treatment or remove and dispose of them.

Preserve

Treatment with an insecticide is an option to preserve ash trees of high value. A healthy, mature ash tree, at least 30 inches in circumference (or 10 inches in diameter) at chest height, and of value to the property owner, may be worth saving. If you decide to treat your ash trees, treatment should begin immediately. Preservation treatments must be administered by a certified arborist about every two years in late spring. Cost will vary depending on the size of your tree, but typically costs from $200 - $300 per tree per treatment.

Anoka County is using a trunk injection of emamectin benzoate to treat high-quality ash trees on county properties. This is an effective treatment option that is not a neonicotinoid, which has been shown to negatively impact pollinators. Emamectin benzoate is specifically formulated to impact the emerald ash borer and, as such, has few if any impacts on other insects. Furthermore, ash trees are wind-pollinated and don’t rely on insects for reproduction.

Removal

In some circumstances, ash trees may not be good candidates for treatment. If 30% or more of the leaves and branches have died or if there are blond patches on the bark, these are signs of heavy infestation levels, and the tree may not be a suitable candidate for treatment. Studies have shown that treating after this level of infestation may not work, and if it does, that tree will need intensive pruning to remove dead or dying wood.