‘Persistent herbicides’ in topsoil, manure, can wreak havoc with gardens

April 14, 2019

The pain spread in unlikely media. The harvest yielded cautionary tales.

And, ultimately, unfortunate circumstances provided a fertile learning experience for advanced chemistry students at Whitefish High School.

The gist is this: Gardeners who feel secure about topsoil and manure probably shouldn’t.

Pat McGlynn, Flathead County extension agent for Montana State University, has heard from residents who have used manure as a soils amendment or acquired topsoil and lived to regret it.

As has Kima Traynham, a Kalispell-based plant science specialist for the Montana Department of Agriculture.

The problem is “persistent herbicides.” They can linger in topsoil, manure and compost and end up whacking back tomatoes, potatoes, peppers, eggplants and the like.

“You’ve got to be so careful about putting amendments on your garden,” McGlynn said.

Acquiring topsoil for gardens and landscaping can have wilting repercussions, she said. And compost piles can be a problem, too, depending upon components.

Sarah Jones and her husband purchased topsoil last spring from a local company for newly laid out garden beds at the couple’s home and separately acquired cow manure from a dairy and manure from friends who raise llamas.

Very little grew in their new garden beds and what did grow looked decidedly unhealthy.

Ultimately, Traynham tested the soils and advised the couple to burn the crops that had managed to grow.

Persistent herbicides were the problem.

“It’s painful to realize your crop isn’t worth the time you’ve put into it,” Jones said.

In the couple’s case, they could not know whether the herbicides came from the topsoil they purchased or from the manure they’d acquired or both.

Jones said the company that sold them the topsoil insisted it was not contaminated. She’s skeptical.

Lisa McKeon purchased a dump-truck load of topsoil from the same regional vendor last spring.

She planted a variety of perennials, some trees and other plants intended primarily for landscaping. She had some topsoil left over that she gave to friends and neighbors.

McKeon said it soon became apparent something was amiss. Some of the plants exhibited symptoms of being affected by herbicides.

“Certain plants showed it more than others but, in general, nothing thrived,” she said. “It was just so not what I was expecting.”

In the Flathead Valley, some growers cultivate hay to be free of noxious weeds for customers who like to ride horses and lead pack animals in places like the Bob Marshall Wilderness and Glacier National Park or attend horse shows that require it.

The bad news is that manure from cows or other livestock fed weed-free hay can include the herbicides that targeted the weeds. The herbicides, such as aminopyralid, can render garden soil essentially hostile to broadleaf plants.

Herbicides can persist in straw and hay and soils.

Taylor Wilmot is facilities and grounds coordinator for the Whitefish School District’s Center for Sustainability and Entrepreneurship.

Last July, Wilmot noticed plants that had been started by students in growing flats and then transplanted into raised garden beds showed signs of being affected by herbicides.

She said there was curling, cupping and twisting of leaves.

Wilmot consulted some friends in farming who suggested testing of the soils in the beds at the Center for Sustainability.

“That’s when I got in touch with Kima,” Wilmot said.

Traynham came to the center in July, obtained samples of soils and plants and sent them to the Montana Department of Agriculture’s analytical lab at Montana State University in Bozeman.

Testing revealed the presence of aminopyralid in soils and plant tissues.

“Once we identified the herbicides with Kima we had to decide what to do next,” Wilmot said. “I started researching some possible methods of remediation.”

She said she thought about all the effort and time that had gone into filling the dozens of garden beds at the Center for Sustainability and imagined the labor that would be required to empty the beds.

Layers of varied materials had been used, covered by topsoil.

Wilmot approached Whitefish High School chemistry teacher Todd Spangler and pitched the idea of advanced chemistry students tackling the remediation conundrum as a class project.

Spangler said he was initially hesitant, believing the scope of the undertaking might be too large and too complex for the class’ 20 students.

But he said the advanced chemistry students jumped right in, beginning with background research about herbicides, about possible remediation strategies, about plant biochemistry and plants that tend to bioaccumulate herbicides, and more.

Ultimately, the class divided garden beds in the Center for Sustainability’s greenhouse into 10 different plots, with one set aside as a control bed where no intervention occurred.

Each of the other plots hosted a different remediation experiment.

Abby Lowry, a senior at Whitefish High School, worked with fellow students Jessica Henson and Ella Greenberg to try a remediation method that used Regenysis and Regenichar, products from regional company Algae AquaCulture Technologies.

Other students focused on cover crops that might absorb the herbicides or the use of microbes that might break down the chemicals in the soil.

Lowry said the research project, a response to the unwelcome news that the soils were contaminated, provided a unique and stimulating learning experience - both for the students and their teacher.

Students had to do background research to understand what questions to ask and how to proceed with potential interventions. It was unchartered territory, she said.

“For once, for the project we’re doing, Mr. Spangler doesn’t know what the answers will be,” Lowry said.

The project required creative and innovative thinking and problem-solving, she said, relying on the sort of critical thinking skills one might encounter in a college research class.

The different remediation strategies launched implementation in early November.

In February, students pulled plants from cover crops, including radishes, peas, oats and sunflowers. Samples of the plants and the test bed soils were sent for analysis to agriculture lab in Bozeman.

Results were recently received and are being analyzed by students, Wilmot said.

“There are still herbicides in the beds, but we did see that some of the methods were more effective than others,” she said.

Wilmot said the research demonstrated that some of the cover crops, including radishes and oats, absorbed herbicides from the soils without exhibiting symptoms.

She said the next step will be deciding how to proceed - whether to embrace one or more of the remediation methods investigated and implemented by students or to remove the contaminated soils.

“I think there is a good chance we will continue with remediation,” Wilmot said.

She said the center will hold a community meeting in May to discuss the research and options for moving forward.

Meanwhile, for regional gardeners wondering whether the soils they intend to plant harbor contamination, Traynham said a prudent approach is to conduct a “bioassay” that can test a random collection of soils through plantings in small pots.

Standard soil testing might not detect some levels of herbicides, she said.

Gardeners can attempt to grow beans, peas or tomatoes, which tend to be sensitive to herbicides, in small pots. The gardeners might also choose to plant some control pots that are filled only with commercial potting mix.

One key is to try to get a true random sampling of the soils.

McGlynn said gardeners who are trying to do the right thing by using manure or fresh topsoil can end up getting burned.

“Be careful, be careful,” McGlynn said.

Reporter Duncan Adams may be reached at dadams@dailyinterlake.com or 758-4407.