Where Are Our Ash Trees Now?

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

Posted: 2018 | Emerald Ash Borer | Insect Control | Spring

The unwanted insect Emerald Ash Borer was an unexpected arrival from Asia in 2001. It has been progressing across the country as the experts have predicted. In general, now all of SE Wisconsin is fully involved. We started to see a significant number of dead Ash trees on the south side of the metro area and in West Bend in 2017. As other deciduous trees leaf out this spring, it will become obvious how the problem has spread by the increased number of dead or thin trees seen.

Biology of the infestation: Trees can be infested for three to five years before they actually die. They can even be infested for a few years and show no symptoms. To a homeowner it is not always obvious. Green Ash trees exhibiting 50% or greater canopy thinning or dieback are not likely to be saved by a treatment. Green Ash that are border line sometimes have additional dieback in the first few years after treatment but then usually recover. White Ash unfortunately do not typically show symptoms of infestation the way Green Ash do. This makes them riskier to treat because they may be below the 50% infestation point (point of no recovery) but they look perfectly healthy. We cannot always tell on White Ash.

Treatment: We are recommending trunk injected Emamectin Benzoate. It is very effective at cleaning up trees and protecting them for two years. We have tried to move all of our treatments to this because research and our experience is showing a very high success rate with Emamectin Benzoate. There are still a few clients using soil systemic insecticides although research shows them as having a significantly lower success rate.

Recommendations: First and foremost is to plant a variety of trees. There will be other invasive insects and diseases in the future. Having a variety of trees will protect you better than any treatment. Many clients have been pleased at how a variety of trees adds to the enjoyment of their landscape with a variety of color, textures, blooms, fruits, etc. Next is to continue treatment of your ash trees to protect the investment you have made. Finally, we can evaluate untreated Ash to see if protection is possible, just contact us.

Future for Ash trees: All of the untreated Ash will die. As the population of the beetles drop off we expect to be able to extend our treatment intervals to three years and then possibly longer at some point in the future. Some level of treatment will likely be needed for Ash trees on an ongoing basis.

While there still may be some new Ash trees we can protect, the numbers are small and the chances of success are reduced. It can be sad to see existing Ash trees removed but it is also an opportunity to improve your landscape with new varieties of trees.