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May 20, 2014

MADISON -- Emerald ash borer is currently the most damaging threat to trees in Wisconsin, according to state forest health specialist who say spring is the best time of year to take actions to protect ash trees.

What you should know

Woodpecker damage
Woodpecker damage.

Know where the pest has been found and look for the signs and symptoms of infestation. "Many people notice a thinning ash canopy, but not until it is too late to effectively treat trees, so it is very important to examine your ash trees early and often," says Bill McNee, forest health specialist with the Wisconsin Department of Natural Resources. Spring is a great time to start. Watch ash trees for the following:

Photos and more information are online at (exit DNR).

What you should do


If you see the signs or symptoms above, get more information or advice and then consider treating your ash tree. Spring is the best time to treat, but the decision to use insecticides is an important one that should not be taken lightly. "Know the facts about your tree's health and the various treatment options before investing in any treatments," says Dr. Chris Williamson, UW-Extension Entomology Specialist.

Remember, this pest only attacks ash trees, and mountain ash is not a true ash.

More information, including UW-Extension emerald ash borer factsheets about treatment considerations are available at To get more advice, you can find a certified arborist in your area at the Wisconsin Arborist Association's website: or in your yellow pages. (all links exit DNR)

Consider the following when deciding whether or not to treat your ash tree

Research shows ash trees can be successfully protected from damage and death due to EAB, but not in all cases. Careful planning is required.

Tree value

D-shaped exit hole
D-shaped exit hole
  1. Determine whether the ash tree is worth treating. Some ash trees are already heavily infested with EAB, too sick to effectively treat, or have major structural problems. Ash trees suffer from many health threats, so knowing as much as you can about the overall health of the tree is an important first step.
  2. IF your tree is healthy it may offer benefits such as increased property value, shade and cooling, and it may contribute to the quality of life in a neighborhood. Consider these benefits along with the cost of treatment.

EAB threat to the tree

  1. Currently, experts recommend that property owners consider treatment if their ash tree is within 15 miles of a known infestation. You can look up communities where EAB has been found at
Emerald ash borer

The cost of options

If EAB is a threat to your tree you can do nothing and take the risk that your tree will eventually die, you can treat your tree if it is still healthy enough, or you can take the tree down and remove it.

  1. The cost of an insecticide treatment can depend on tree size and health condition.
  2. The options for treatment require ongoing commitment. Almost all insecticide options require you to repeat treatment annually. One option called "Treeage" offers three years of protection but can only be applied by a licensed professional.
  3. The cost of removing or replacing trees should also be weighed. You may be able to treat your tree for many years and spend less money than it would cost to remove that tree.

FOR MORE INFORMATION CONTACT: Bill McNee, Wisconsin DNR, 920-893-8543 or Chris Williamson, University of Wisconsin Extension, 608-262-4608

Last Revised: Tuesday, May 20, 2014

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