Taking care of our trees

The emerald ash borer and options for managing ash trees

Trees are important in our community as they provide numerous benefits. Trees improve our air and water, improve our health, reduce urban heat, provide wildlife habitat, save energy, and increase property values.

The biggest current threat to our tree canopy is the emerald ash borer, which is an invasive tree pest from Asia that kills ash trees. Ash trees are a common urban landscaping tree — there are more than one million ash trees in yards, parks and streets in Hennepin County, making up about 15 percent of the tree canopy. All of the ash trees in the county are threatened by the emerald ash borer, and it is likely that the number of ash trees infested and dying from the emerald ash borer will increase greatly in the next five years.

Most residents of Hennepin County live within 15 miles of an infested ash tree. So if you have ash trees on your property, it’s time to start thinking about what you’re going to do with those trees.

What is an ash tree?

The first step in preparing for the emerald ash borer is determining if you have any ash trees on your property. Look for the following characteristics to determine if you have an ash tree:

• Branches that grow directly opposite from one another
• Multiple leaves on one stalk joined to a branch
• Bark with diamond-shaped pattern

Visit www.dnr.state.mn.us/invasives/terrestrialanimals/eab/idashtrees.html for more detailed identification information.

What are the signs of an emerald ash borer infestation?

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

• Leaves on the top or on one part of the tree will start dying, eventually impacting the rest of the tree
• Sprouts growing from the roots or base of tree, as this indicates that the tree is stressed
• Increased woodpecker activity
• Cracks in the bark
• Serpentine patterns underneath bark and D-shaped holes

What can I do about infected 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.

Preserving ash trees

Treatment with an insecticide is an option to preserve ash trees of high value. 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 cost about $200.

Hennepin County is using a trunk injection of emamectin benzoate to treat ash trees on county properties. This is an effective treatment option that, unlike other insecticide options, is not a neonicotinoid, which have been shown to negatively impact pollinators.

Removal and disposal

Any ash tree that is not being treated will eventually need to be removed by a certified arborist and disposed of properly. If you decide to proactively remove ash trees, remove trees between October 1 and April 30 to avoid the season that the emerald ash borer is active and in flight. Ash tree waste should be disposed of at yard waste sites nearby to prevent spread of the emerald ash borer. Find yard waste disposal sites at www.hennein.us/yardwaste.

Replanting

Because of the numerous benefits trees provide, replanting new trees in place of any you will have to remove is a great idea. When planting trees, select a diversity of trees that are well-suited to your growing conditions.

See the Tree Owner’s Manual from the U.S. Forest Service at www.treeownersmanual.info for more information on selecting and planting trees.

This information was provided by Hennepin County Environment and Energy, Environmental Education & Outreach.