Treating Ash for Emerald Ash Borer

by Dave Scharfenberger, Board-Certified Master Arborist WI-0131B

Emerald ash borer (EAB) is a very serious problem that threatens all ash trees in the Midwest. It has not been found in Wisconsin as of June 21, 2006, but it is in northern Illinois. The million-dollar question seems to be, “When should I start treatment if I want to protect an ash tree?”

Unfortunately, there are differing opinions on this question and the actual facts are not fully conclusive. Most of the money ($100 million+) that has been spent on EAB has gone into removal of trees with the hope of eradication. Little has been put towards research to develop trapping methods and a better understanding of the EAB life cycle. There is still much to be learned.

One important point to remember is that you have time to deal with this! It has not yet been found in Wisconsin. It is very unlikely that a diagnosis or treatment options today will be any different than in September (or possibly next spring, or even later).

Important points to consider about treatment:

  • In our opinion, only high-value, important trees should be considered for treatment, i.e., specimen trees, ones shading your home or patio, etc. Also, trees should be healthy.
  • Imidacloprid has been shown to protect trees from EAB. It is not 100% effective (nothing in nature is!). Studies suggest it is 85% effective. It is best if the treatment is in place ahead of insect pressure but can be done afterward if the tree is only slightly infested (effectiveness may be reduced).
  • If the state is doing eradication cutting and your tree falls into the area, the state will remove your tree even if it is treated. The use of eradication cutting by the state will be evaluated on a case-by-case basis.
  • The treatment will need to be done yearly, or the tree will lose protection, so cost may be a factor.
  • Treatment does not have to be trunk-injected to work. Trunk injection should only be done in emergency situations. Trunk injections do damage and stress trees. Yearly trunk injection is not good tree care. Soil injection provides protection without damaging the tree.
  • Imidacloprid will not control most native ash borers (clear wing borers) but will control leafhoppers and plant bugs. Proper diagnosis is important if other problems exist.
  • Multiple insecticide trunk sprays have been shown to be effective and are also treatment options.
  • Planting replacement trees is also an option to consider instead of treatment.

Misdiagnosis could be a big problem. Do not remove a living ash tree because of EAB unless you are sure of what is wrong, because there are several look-alike problems. There are also many other problems with ash trees this year due to the wet spring and the past several years of drought. Most will not warrant removal. If trees are infested, they will need special handling. Take time to properly assess the problems and collect all of the relevant facts before you take any action. Remember – you have time!

When should treatment be started? Some people say you could be wasting money and materials in treating when EAB is not very close. Others will point out that early protection is most effective, and without good trapping methods, we do not know where EAB is for sure. Everywhere EAB has been found, it had been present for three to six years! What is right for one person, may not be right for another.

You should have all of the facts before you take removal or treatment action. Your Wachtel Certified or Board Certified Master Arborist can provide those facts and give sound, trusted advice.

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