Attack Of The Clones: Ohio Researchers Find New Hope For Fighting Ash Borer

May 23, 2018

At the U.S. Forest Service’s Northern Research Station near Delaware State Park, Jennifer Koch guides an off-road vehicle down a winding path that opens to a large, fenced-in area of young trees.

But not just any trees: Koch and other researchers with the Forest Service hope this plot could hold one of the keys to the survival of the ash tree in North America.

Koch has spent the last several years studying what are known as lingering ash - trees that have fared much better against the emerald ash borer. The invasive beetle, which came to North America from Asia about 20 years ago, has killed millions of ash trees around the Midwest. 

But for reasons that researchers are learning more about, some trees have survived.

“So they were all selected (for our research) because there were in areas where ash (borers) had already come through and killed probably over 99 percent of trees in that stand, but they remained alive and had healthy canopies," Koch says.

Koch says they’ve identified at least two reasons why. Lingering ash seem to attract fewer hungry adult ash borers, which means they’re less likely to become homes to eggs. And when eggs do hatch on lingering ash trees, they tend to be smaller and have a higher mortality rate.

The squiggly lines, also known as the gallery, left by the emerald ash borer.
Credit Steve Brown

Those are extremely valuable characteristic for modern ash trees, so Koch is making sure they get passed on through cloning. Not genetic modification, but rather clonal duplicates of lingering ash literally cut from part of the parent tree.

Koch points out a healthy tree that’s surrounded by others killed by the ash borer.

“We have grafted from this tree so we can keep it alive through its clonal replicates that are vegetatively propagated, and they continue to use it for breeding purposes," Koch says.

Maybe most importantly, Koch says the cloned trees appear to be even more resistant to the ash borer. With their cloned trees healthy and growing, researchers are waiting on the next generation of seeds to see if they’re even more resistant than their cloned parents.

Lingering ash trees sit in a greenhouse at the Northern Research Station in Delaware County. The best-performing trees will eventually be transplanted into the nearby orchard.
Credit Steve Brown

Koch says she thinks the Delaware research station is the only place in the country using a traditional tree breeding approach to fighting the ash borer.

Could her work could save the ash tree in North America?

“Yeah, that’s exactly our goal, is to save ash as a species and get it to a level that it’s a sustainable, healthy species that we can retain in our North American forests," Koch says.

Koch says they plan to add more lingering ash seedlings into their on-site orchard this year. Ash trees planted from seed typically take seven to 10 years to begin giving off seeds of their own, so it could be another decade before Koch knows just how successful their ash tree breeding program can be.