News Flash

City of Rosemount

Posted on: May 29, 2018

Emerald Ash Borer detected in Rosemount

Borer damage photo

An insect that threatens ash trees has been detected in Rosemount. The Minnesota Department of Agriculture (MDA) on May 18 confirmed the presence of emerald ash borer (EAB) on private property just south of Rosemount High School. The affected tree had been reported to the City by a homeowner.

Rosemount is in an area covering much of the Twin Cities metro that the MDA considers “generally infested” with EAB. The invasive insect has already been detected in most communities surrounding Rosemount.

The City of Rosemount approved a plan in 2013 to begin removing ash trees from public property. So far crews have replaced about 250 ash trees with other species in City parks. About 700 ash trees are in the public right-of-way along City streets. City crews have removed more than 250 of these boulevard ash trees since 2014.

The City will continue to remove boulevard ash trees in the early spring and fall. Affected property owners will receive a letter before their tree is removed.

Owners of homes and other private property are responsible for treatment or removal of the trees on their land. Owners may need to make choices soon about whether to protect their ash trees or have them removed.

Treatment with pesticides

If an EAB infestation is caught early enough, a pesticide treatment may save the ash tree from this pest. The products currently available can prevent EAB from infesting healthy ash trees and may save ash trees in which EAB numbers are still relatively low. In order to provide ongoing and long-term protection to ash trees, however, the treatments must be repeated at least every two years for the life of the tree.

The recommended type of treatment is trunk injection. Residents should make sure the contractor hired to perform the service has a commercial pesticide applicator’s license.


Ash trees that are heavily infested with EAB or that have other problems should be removed as soon as possible, but not during the summer. The MDA indicates removal should take place between October 1 and May 1. Delaying until damage to a tree is widespread may make removal more expensive.

What are the signs of infestation?

  • First, be sure you’ve identified an ash. EAB only feeds on ash trees. Ash trees have “opposite branching,” meaning branches come off the trunk directly across from each other. On older trees, ash bark has a tight, diamond-shaped pattern. Younger trees have relatively smooth bark. Guides to identifying ash trees are available on the City’s EAB webpage,
  • Once you’re sure you have an ash tree, look for woodpecker damage. Woodpeckers eat EAB larvae, and woodpecker holes may indicate the presence of EAB.
  • Infected trees often have cracks in the bark. EAB larvae tunneling under the bark can cause the bark to split open, revealing S-shaped tunnels.
  • Contact a professional tree contractor. Rosemount Public Works can also offer a check; phone (651) 322-2022.

EAB kills ash trees by tunneling under the bark and feeding on the part of the tree that carries nutrients through the trunk. Minnesota has approximately one billion ash trees at risk – the most of any state in the U.S.

EAB often spreads from people moving firewood or other products harboring larvae. To help stop the spread, don’t transport firewood. Buy firewood locally from approved vendors, and burn it where you buy it.

For more information on emerald ash borer visit The City also plans to host an open house on issues related to the infestation later this summer.

The accompanying photo, taken by City staff, shows damage beneath the bark of the tree in which EAB was detected.

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