Emerald Ash Borer in De Pere

What is Emerald Ash Borer?  Emerald Ash Borer (EAB) is an insect that affects all varieties of ash trees by boring holes through the tree and bark.  The damage done by the insect progressively kills the tree. 

History of EAB in De Pere:  In the late 1990’s and early 2000’s EAB was virtually unknown.  In 2004, information began to circulate about this insect that was accidently introduced in the US from Asia.  The City of De Pere, as well as many other municipalities, began to discontinue planting all ash tree varieties (green, white, black; Mountain ash is not a true ash and is not affected) in response to the threat of EAB.  In 2009 EAB was positively identified on Green Bay’s north side.  In 2016 De Pere positively identified EAB in a location on our far NE side, with subsequent findings occurring in numerous other E and W side locations (see the attached map).

What is going to happen?  Research has indicated once EAB is detected, virtually all the ash trees in the area will die off within a span of 10-15 years.  This 10-15 year die off is something the Wisconsin Department of Natural Resources has projected based on its experience with the insect and infestations in other parts of the country.  The 10-15 year die off acts in a bell curve: 1) the first 3-4 years there is not much damage visible to the public and die off is minimal; 2) the middle part of the 10-15 year span witnesses a rapid die off, and then; 3) the final 3-4 years is a trickle effect of remaining trees dying.  Based on the information we have as of 2019 the City of De Pere is about 4-6 years into the 10-15 year cycle.  Unfortunately, this means we are projecting a rapid die off of our ash trees over the next 4-5 years. 

How many ash trees do we have in the City?   The City currently has approximately 1100 ash trees in our streets, 100 in our parks and 500 in our ‘wild’ areas.  Although we do not inventory or count private trees the number is typically 5-10 times the amount found on public grounds.

What is the City doing?  Since finding EAB the City has been scouting extensively for signs of the insect and aggressively removes those ash trees that have those obvious signs.  This helps to slow the spread of the insect.  Since 2016 we have removed approximately 125 infested trees and that list unfortunately will continue to grow.  To be clear, we only remove healthy ash if there are legitimate concerns or reasons (construction, defects).  We have also been working with the WDNR on the release of tiny parasitoid wasps that only attack EAB larvae.  We were instructed to release them in areas with high concentrations of ash – East River Trail & Nature Preserve – to help slow the spread in these wild areas.  The wasps will not eliminate nor eradicate the pest; however they do slow it down slightly to allow communities to prioritize their resources.  Lastly, staff continues to search for grants to provide funding for the replacement of ash trees as we take them down.  The City has been fortunate to have planted over 500 trees throughout the City since we discovered EAB to begin the replacing the lost benefit of the ash trees that will need to be removed. 

Is there a cure?  Unfortunately at this point, there is no known cure for the infestation of EAB.  There are chemicals that can be injected into ash trees which have been proven to work effectively.   However, the treatments are not guaranteed to save the ash tree, are costly, and need to be done either yearly or every two years (product dependent) in order to be effective.   

As a homeowner what should I do or what can I do? 

  • We recommend that you inspect your property to determine if you have any ash trees.
  • If you do have ash trees, we recommend you inspect the tree for signs of EAB. If you find evidence of EAB, we encourage you to contact the City Forester.   You can personally inspect ash trees by using the following guidelines:
    • Look for obvious signs of the insect. These include trunk sprouting; cracking of the bark; dieback in the crown; thinning of the crown; “S” shaped galleries under the bark where the larvae feed; “D” shaped exit holes where the adults emerge; and extensive woodpecker damage or ‘flecking’ that takes place when they are looking for the insect under the bark (see attached picture ).
  • If you positively identify a tree or trees in your yard that are infested with EAB, we strongly recommend you look into removal. It has been shown that trees dying from EAB quickly deteriorate and become brittle sooner than trees that don’t die from EAB.  This could cause branches or the entire tree to break off and fall causing personal harm or property damage.
  • If you are planting trees in your yard, we highly recommend that you do not plant any form of ash tree but look to plant a diverse population of trees.
  • Consider chemically treating high value trees in your yard, if the trees are healthy and viable. You can treat trees yourself (be sure to read label instructions carefully) with products available locally if your trees are under 47” in circumference (or 15” dbh ).  If they are over that size the tree will need to be injected by a licensed chemical applicator with products that are not available to the general public.  The effectiveness of the products will vary based on timing and health of your trees so it may be helpful to contact a local professional or horticultural agent for their opinion and/or guidance.


More information on this devastating insect can be found at various sites including: