Emerald Ash Borer — Is There Any Hope for the Future?

By Christian Nelson

In the early 2000s, a deadly plague struck the ash trees in southeastern Michigan – quickly wiping out tens of thousands of ash trees and eventually spreading to at least 38 states. Millions of ash trees have been killed since then, and the numbers keep growing. The cause? The emerald ash borer, a small, invasive insect that was accidentally imported to the U.S. from China. Researchers have tried everything: insecticides helped a bit but nowhere near enough. Cutting down thousands of healthy trees to create a sort of “firebreak” failed to stop the spread of the insect. They even imported a natural enemy of the emerald ash borer, which helped, but not enough.

The situation was and is dire. But is there any hope? Yes! As Kathleen Knight, a research ecologist with the U.S. Forest Service explained there is a glimmer of hope. Appearing on Daniel Wanschura’s “Points North” podcast, she describes the moment when she and some of her researchers spotted what looked like a living ash tree in an area where countless ash trees were all dead. Is it an ash tree? Could it be? It looked like an ash. It definitely was an ash. Healthy and full of green leaves. Kathleen wondered how could this tree possibly be there alive and flourishing after everything else they had seen there that day?

In 2010, Kathleen put together a team to see if they could find more ash tree survivors – and they did! Finally, with more to work with, she contacted Jennifer Koch, a geneticist working for the U.S. Forest Service, who is also an expert in the study of ash trees. At first, Koch was skeptical, thinking that all data showed that no ash trees were going to survive. There was no resistance to the deadly insect. But then, after seeing Kathleen’s field data and the pictures she had taken of the healthy trees she had found, Jennifer started thinking they might actually be onto something.

Eventually, Jennifer and her team came up with the idea that some ash trees in North America have a genetic resistance to the emerald ash borer. But Jennifer knew that was just a hypothesis and that they needed more data. “We’re scientists, so we’re skeptical,” she said.

As Kathleen continued finding a few more of the “lingering ash trees,” she brought some of the branches back to Jennifer, who cloned some of the survivors, and discovered that the trees had a resistance to the emerald ash borers. And, amazingly enough, along with the resistance, they also could actually kill the larvae of the emerald ash borers.

While it will take a long time to create an entire orchard of resistant ash trees and harvesting the seeds and planting seedlings in forests across the region – probably a decade or so – this is hope. Real hope. Hope that the beautiful ash trees will be saved, and that millions of borer-resistant trees will restore the forests around the country. §

The image on the Home page shows a green ash. By the summer of 2008, emerald ash borer had spread to Wisconsin. There are four types of ash trees in Wisconsin:

• White ash (Fraxinus americana), common in drier upland soils, features reddish-purple fall foliage.
• Green ash (Fraxinus pennsylvanica), prefers wet sites and is widely planted as an urban street tree.
• Black ash (Fraxinus nigra), predominantly found in northern swamps and lowlands.
• Blue ash (Fraxinus guadrangulata), rarest and the most emerald ash borer-tolerant species, found mostly in Waukesha County.

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