Like a kid watching a summer thunderstorm slowly rolling in and wondering how long until the rumbles would be directly overhead, I’ve had a morbid fascination with watching the progression of the emerald ash borer in the Midwest for over a decade. Although emerald ash borer wasn’t found in Wisconsin until 2008, my connection with EAB precedes that by a few years. It turns out my first job as a budding entomologist was as a summer intern for UW-Extension looking for signs of the insect in the state during the summers of 2005 and 2006. Fast forward twelve years and that storm is finally overhead, at least in my neck of the woods. I knew such a time would come, but it really hits close to home when the sounds of chainsaws mark the final days of your neighborhood’s ash trees—at least the ones that aren’t being treated.
At the time of writing, 42 counties in Wisconsin have been quarantined for EAB. While the southeastern part of the state has already been hit hard (green on the map above), a large chunk of the state has not yet seen the emerald ash borer or has only seen light pressure (click the map above to see more details on this topic). Unfortunately, this means that the emerald storm will only be getting worse over the coming years. Along these lines, when EAB first arrived in Wisconsin, spread was slow and the annual number of new community-level detections was small. However, as the populations of this insect have built up in the state, the number of new detections has increased dramatically as illustrated below:
Unfortunately, the outlook for the Midwest’s ash trees doesn’t look good and we’ll still be dealing with this insect for years to come. Ironically, this isn’t the first time that we’ve watched a scenario like this play out. As the baby boomer generation grew up, they watched as elms were devastated by the likes of Dutch elm disease. As with emerald ash borer, Dutch elm disease had significant impacts on forested and urban areas and led to irreversible changes in the landscape around us.
With all this Doom-and-Gloom, is there a light at the end of the tunnel?
Possibly—but it may be a ways off. For the time being, there are insecticide treatments available that can maintain the health of ash trees, although treatments are costly and are only feasible for relatively small numbers of trees. Biological control is being explored as a potential way to control EAB populations, although results have been limited thus far. However, with any biological control program, it can take years to work the kinks out of the system and see results.
A long-term plan may be to develop varieties of ash trees that are resistant to attack by the emerald ash borer. In several locations in Ohio and Michigan, scientists have found a small percentage of “lingering” ash trees that have survived the initial onslaught of EAB and are monitoring those trees over time for continued survival and genetic traits that may help stave off infestations. Interestingly, one particular species of ash (blue ash, Fraxinus quadrangulata) may hold important clues for long-term ash survival. In some spots in Michigan, >60% of blue ash trees have survived in areas attacked by emerald ash borer. While tree breeding programs may ultimately develop a resistant ash variety, this is likely years away and for the time being we’ll have to face the emerald storm.