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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 December 23, 2014, Minnesota Department of Agriculture staff confirmed an Emerald Ash Borer infestation in Lebanon Hills Regional Park in Eagan. This is the first confirmed infestation of EAB found in Dakota County, and now Dakota County has been added to the metro quarantine zone, which also includes Hennepin and Ramsey counties.  Dakota is the sixth county in the state to be quarantined: three now in the metro area and the other three (Houston, Winona, and Olmstead counties) in far southeastern Minnesota.  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.

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 then 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 reapplied for the natural life of the tree.

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 early 2015, approximately 150 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 135 ash trees have been removed from boulevards.  In the case of boulevard trees, when an ash tree has been removed, a replacement tree is offered to the homeowner but not every tree removed is being replaced. 

Removal and replacement are 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 the Arrest the Pest Hotline at (651) 201-6684.  For more information, click on one of the links listed below: