Iowa’s white oaks are dying. New test kits could show why.

COLO — More than a decade into a mysterious epidemic killing off white oak trees, Iowa foresters hope a new test kit will help them quickly screen trees in the field for half the cost of laboratory tests.

Inspired by COVID-19 rapid tests, a Minnesota startup developed a kit that amplifies the DNA of a fungus spreading among oaks weakened by drought. The Iowa Department of Natural Resources hopes to use information gathered from these kits to isolate infected trees and protect others.

“A lot of people are concerned about this white oak decline,” said Tivon Feeley, Forest Health Program leader for the Iowa DNR. Foresters want to know whether they should replant white oaks or choose other species. “Right now, I can’t tell them. (But) this test gives us a lot of tools we can start using.”

Background

Around 2010, foresters across the Midwest started noticing centuries-old white oak trees dying off in just one season and didn’t know why. Oak wilt, a fungal disease spread by insects or through the root systems of infected trees, was a possible culprit, but most foresters hadn’t seen it be so fast or so deadly.

“With this oak decline, we have two to three dead trees almost every other acre,” Amana Society Forester Tim Krauss said in October 2022. “We have to harvest the dead trees because we only have a year until they are no good. We can make our budget by just cutting dead trees. The downside is, they are not coming back.”

When 200-year-old and 300-year-old giants are felled, increased sunlight on the forest floor causes an explosion of invasive species and less-desirable trees, including hackberry and elm, Krauss said.

Climate change has played a role in the rapid decline of white oaks, with drought making the trees more vulnerable to disease or pests.

The U.S. Forest Service and the Canadian Council of Forest Ministers planned a pilot project with a new test kit to quickly determine if a tree has oak wilt, but efforts to develop the kits at the University of Toronto fell through in 2023.

What’s happened since

Abdennour Abbas, a professor of nanotechnology at the University of Minnesota, stepped up in 2023 with PureBioX, a St. Paul, Minn., startup that develops rapid tests for use in health care, pharmaceutical, food and agricultural industries.

“The regular test is a cell culture and it takes a very long time,” said Anil Meher, a PureBioX analytical chemist who last week visited Iowa for a trial of the oak wilt test kits at Hickory Grove Park near Colo, in Story County.

When plant diagnostic laboratories test trees for oak wilt, the results can take two weeks to two months and cost $70 to $300, the Iowa DNR’s Feeley said. PureBioX’s test kits take one hour and cost about $30 each.

“It’s quite simple so you can do it in the field setting,” Meher said.

Mark Runkel, an Iowa DNR forest health technician, and John Mullen, a GIS analyst for the department, walked out into a stand of trees at Hickory Grove to look for white oaks with signs of oak wilt. The outer leaves may turn brown, while the veins stay green. And when a branch of an infected tree is removed, the cut ends smell like fermented fruit.

From each tree, they gathered a cluster of leaves, a branch and a 3-inch trunk core. If the tests of leaves are effective in determining infection, future tests won’t require branches or trunk cores.

Mullen marked the locations of the trees in a tablet and gave each a unique ID. Mapping the infected trees is an early step to determine how oak wilt might be spreading.

Meher and Feeley put each sample into a tube with chemicals that break down the tree matter. Meher extracted the DNA and put it into a tiny vial, which is heated on a portable pad to amplify the DNA. If the Bretiella fagacearum fungus, which causes oak wilt, is present, the liquid will turn yellow. If the fungus is not present, the liquid turns pink.

If foresters find isolated trees with oak wilt, they could spray herbicide on those trees in hopes of halting the transmission through underground root systems, Feeley said.

The team plans to test trees in the Amana Society’s 7,000-acre timber, in Marshall County, in the Loess Hills in Western Iowa and in the Des Moines area. They also are putting out insect traps in forests with oak wilt to see what kinds of bugs might be carrying the fungus. Results of these studies will go into the 2024 Forest Health report.

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