Jeffrey Hahn, University of Minnesota Asst. Extension EntomologistWith the discovery of emerald ash borer (EAB) in Minnesota last year, people with ash on their property are concerned about possible attacks from EAB and what they should do, if anything, to protect their trees. Insecticides are an effective method to protect your ash from EAB but does this mean this is what you should do? There are a number of factors that people should consider when weighing their options.
The first factor you should consider is how far are you from a known EAB infestation. The general guideline is that the highest risk from EAB occurs when you are within 10 -15 miles from a known infestation. Right now, EAB is only confirmed in St. Paul and Minneapolis. This means that essentially all of the Twin Cites metropolitan area is at a high risk. However, if you are in Minnesota outside of this 10 - 15 mile radius, the risk from this exotic borer, while not zero, is much smaller and treating your ash for EAB is not suggested.
You should also ask yourself what condition is your ash in. When trees are healthy or at least mostly healthy, i.e. dieback or decline in the canopy does not exceed 40% - 50%, they are a possible candidate for treatment. If the trees are in poor health and the canopy shows over 50% dieback or decline, it's not worth saving the tree. Also, when a tree has suffered significant girdling damage from borers, its ability to move insecticide through the tree to protect it is greatly reduced.
How valuable is your ash to you? Does it provide shade for your house; is it an important part of the aesthetics of your yard; does it has sentimental value? Or is it just another tree in your yard and it wouldn't be missed? The more valuable your ash is, the more likely you will try to save it.
You should balance these factors with the cost of treating trees versus the cost of removing and/or replacing trees. When considering insecticides, remember that the cost will vary according to how large the tree is, how many trees you are treating, what insecticide is being used, and the fees charged by individual companies.
It is very important to remember that once you start using insecticides, it is a long term commitment and you need to continue to treat your ash regularly (every 1 - 2 years) for the life of the tree. Ash do not develop any resistance when they are treated, so if you stop using insecticides after a number of years, they are just as vulnerable to EAB as they were before you started to treat them. So while the cost of a removing a large ash may be considered to be expensive by some, it is a one time cost compared to the ongoing, long term price of treating trees.
What is the right action for you to take? There isn't one right answer. What a person may do will depend on their particular circumstances - the right solution for one property owner may not be appropriate for someone else. However, consider the above factors to help you make a decision that is right for you.