Emerald Ash Borer

The emerald ash borer (EAB) is a small wood-boring insect that is devastating the ash tree population across the eastern US. First discovered in Michigan in 2002, EAB has killed tens of millions of ash trees in that state alone and has been spreading from the Great Lakes region ever since. When the first EAB infestation in Minnesota was confirmed in St Paul in May 2009, ours was the 11th state with a known EAB infestation

On May 18, 2018, the Minnesota Department of Agriculture (MDA) confirmed an infestation by EAB of a tree on private property near Rosemount High School. Since the first EAB discovery in Dakota County, in Eagan in 2014, it has been confirmed in most other cities in the county. 

After the initial discovery in Eagan, Dakota County was added to the metro quarantine zone, which also includes Hennepin and Ramsey counties. Once a quarantine zone is established, no ash materials (logs, branches, chips, stumps) can be transported out of the quarantine zone. Ash materials can be brought into the zone and moved within the quarantine area, but not shipped out of it. There are currently fourteen counties in the state that have been quarantined; seven in the metro area, six in the far southeastern corner of the state and St Louis County around Duluth.

Symptoms and treatment

The larvae of the emerald ash borer kill ash trees by feeding in the cambium layer between the bark and the wood, producing galleries that eventually girdle and kill the tree. It generally takes 2-5 years after a tree is first infested for the number of borers under the bark to grow to levels that they damage and eventually kill the tree. Some of the symptoms of an emerald ash borer infestation in a tree are:

  • Bark that is splitting
  • Increased woodpecker activity in the tree
  • D–shaped exit holes in the bark
  • S–shaped galleries under the bark
  • Dieback of leaves and branches in the upper one-third of the tree
  • Sprouts of new growth from the trunk and roots, often with larger than normal leaves
There is currently no cure for this pest but there are chemical treatments which, when applied to individual trees, can prevent infestation and protect the tree for a limited time. All of the treatments currently available are effective for only one or two years and must be applied repeatedly for the natural life of the tree.

Treatment in Rosemount

Owners of homes and other private property are responsible for treatment or removal of the trees on their land.

In Rosemount, rather than treat ash trees on public property, for the last few years we have been selectively removing ash trees form our parks and boulevards. As of spring 2018, approximately 250 park trees have been removed and replaced. In 2012, Rosemount received a $20,725 grant from the Minnesota DNR intended to increase tree diversity within the City, and this grant has helped greatly with the planting effort. At the same time, approximately 250 ash trees have been removed from boulevards. 

Removal is just one of the many strategies available to manage our urban forest and protect our tree cover. Now that EAB is in our area, private property owners should start to consider the ash trees on their property and decide if they would like to protect them or if they can accept the probable loss of these trees.

If residents suspect a tree is infested with EAB, they are encouraged to contact a professional tree service or Rosemount Public Works at (651) 322-2022. For more information, click on one of the links listed below: