Can researchers save the Pacific Northwest mint industry?

This article originally appeared on Capital Press.

INDEPENDENCE, Ore. — Scott Setniker drove over the windrowed field of peppermint toward a large harvester pulling a boxcar-like white trailer.

The first day of the Setniker Farms peppermint harvest in Independence, Ore., was a slow one. They likely wouldn’t reach their goal of filling 100 trailers but Setniker wasn’t fazed. It was all part of the harvest.

Setniker’s farm is one of only a few mint growers left in Oregon’s Willamette Valley, but it is also one of the biggest. He is a third-generation farmer, and his family has grown mint on this land since the 1980s.

But shrinking yields are a continual struggle, and although he has been able to manage it, he worries about the future.

Setniker, along with about 300 other peppermint growers around the Pacific Northwest, is facing the problem of disappearing acreage where peppermint can grow.

The reason: verticillium wilt.

True to its name, verticillium wilt can make mint plants wilt, turn yellow and distort their growth. This, in turn, means lower yields for mint growers.

Peppermint — and specifically an heirloom variety, Black Mitcham — is used in chewing gum, toothpaste, ice cream and other mint-flavored products. But peppermint plants are especially susceptible to verticillium wilt. To combat this, a team of researchers is exploring ways to protect peppermint against the fungus that causes the disease.

New varieties ahead

In a laboratory at the University of California-Davis Genome Center, project scientist Isabelle Henry and her team of researchers hope to eventually produce new varieties of Black Mitcham that can better withstand verticillium wilt.

“The industry is at risk because Black Mitcham is sensitive to this fungal pathogen,” Henry said.

In the year or so since their laboratory received funding from the Mint Industry Research Council, the researchers have made significant progress, Henry said. There is still a lot left to do, but they are a step or two closer to finding a pathway to resistance to a disease that is becoming a bigger problem for mint growers.

Mint history

Peppermint originally came to the U.S. from England in the early 1800s. It was first grown in the eastern U.S., but as the soil there became infested with the fungus that causes verticillium wilt, raising it became infeasible. Once the fungus is present in the soil, it doesn’t go away.

As a crop, peppermint migrated westward as growers tried to stay ahead of the fungus. Now it is primarily grown in the Pacific Northwest.

Peppermint plants are sterile and do not sexually reproduce; they propagate as clones with their roots, so there has been no adaptation over time to the fungal threat.

But now that peppermint has reached the West, there are few other places for it to go in the U.S. The U.S. exports about 36% of the world’s peppermint oil, with Idaho, Washington and Oregon leading the country in mint production.

The fungus is now found the soil in many Pacific Northwest fields, causing yield loss for mint growers in the region. Oregon has especially suffered, as the state has less wilt-free or “virgin” soil.

Like a fine wine

Trying to address these challenges, Henry’s team has been mapping the genomes — the genetic material — of Black Mitcham and its main parent plant, water mint.

Mint oil is like wine, Henry said. The balance of each component determines the taste and smell. But Black Mitcham is not just any wine — it’s “like a very specific Merlot” because its genetic makeup is unique. That makes it difficult to recreate.

She hopes that identifying where different traits originate in the genome will allow her team to determine which genes are associated with composition and taste and which may offer increased resistance to verticillium wilt.

Mint mutations

Additionally, the researchers are planning to compare Black Mitcham’s genome to mutated varieties of the plant that are more resistant but don’t have the right oil composition. The regions in the two plants’ genomes that differ may indicate which ones offer resistance.

This could lead to developing a disease-resistant strain of Black Mitcham that doesn’t lose yield, composition, or taste either by using gene-editing techniques or by creating fertile peppermint plants through doubling their genome, which might allow them to sexually reproduce.

However, these interventions are still a few years away at a minimum, Henry said.

Right now, the team has finished sequencing the genome of water mint but is still working to identify which parts are responsible for various qualities in peppermint. They are also beginning to compare the parental water mint genome to the mutated Black Mitcham plants that have higher resistance.

Henry and her team are still sequencing the traditional Black Mitcham genome, which she expects to complete in the next few months. Then they’ll be able to compare the mutated and original Black Mitcham plant genomes.

They are also working on doubling the genome of Black Mitcham, which could allow the plant to reproduce sexually and then do marker-assisted breeding to cross peppermint with other mints. The resulting varieties would hopefully be disease-resistant while keeping the oil composition and taste.

So far, the researchers have seeds with doubled genomes and they have crossed seeds, but they do not have any crossed plants yet, so Henry can’t tell whether the experiment is working.

“Several of the steps have happened successfully that we weren’t sure about,” she said. “The next big question is going to be: what kind of oil do these progeny produce?”

If the crossed varieties produce oil that is similar to Black Mitcham, it could have big repercussions.

“Farmers, and I think the industry, want to see new mint clones,” Henry said. “They want to see something to replace Black Mitcham in their fields that is more resistant, and so this is one way to get there.”

Mint economics

John Reerslev, a mint grower in Junction City, Ore., faced the challenge of verticillium wilt and lost.

He said verticillium wilt has been “heavily devastating” to his land, so much so that his farm no longer grows any Black Mitcham peppermint. Instead, he grows a proprietary variety that has a similar oil and is more resistant to the disease.

Reerslev has seen a decline in mint oil production in the Willamette Valley, and a USDA report backs his observation. Nationwide, peppermint oil production is 3.35 million pounds, only 53% of the 6.27 million pounds produced in 2013.

The acres of peppermint harvested nationwide have decreased over the years. In 2012, about 76,900 acres of peppermint were harvested, but by 2022, it had dropped to 34,000 acres, according to the USDA’s crop production reports.

Some of the decline is due to foreign mint oil’s lower prices, which makes it harder for U.S. growers to compete.

But beyond that, it’s expensive to grow and distill mint, and when the yield is decreasing due to wilt, it becomes that much harder to justify.

If researchers can find a way to reduce peppermint’s sensitivity to the fungus while maintaining the qualities of the plant that growers and end-users value, then the threat of verticillium wilt will be greatly diminished and mint yields will increase.

Setniker, the mint grower, said that as mint production moves into a new area not affected by verticillium wilt, as it has in Idaho, states that have wilt struggle to keep up.

“It’s a little bit harder to compete, then, if Idaho can get 20 or 30% more oil per acre,” he said. “They can sell it at a lower price, then it kind of pushes the price down and pushes out the areas where you have not as good of soil.”

Furthermore, Setniker said, much of his mint oil goes to Colgate-Palmolive, a large manufacturing company producing household and personal care products. Colgate-Palmolive, along with a few other major companies, contract the mint from growers.

“They’re very selective on their characteristics, and so even if (researchers) come out with a very resistant one, if the molecular makeup isn’t right, it still doesn’t necessarily do us any good. That’s what makes it such a hard task,” he said.

Hope for the future

Steve Salisbury, the Mint Industry Research Council’s research and regulatory coordinator, echoed Setniker. A new variety of peppermint could offer new opportunities, he said, since growers have made such big investments in stills and machinery for oil production, and there are fewer chances to plant in virgin soil.

With all the possible impacts in mind, the MIRC thinks the results of Henry’s research so far are promising, Salisbury said.

“A new variety could potentially produce a new opportunity for sustainability of our mint growers and the mint industry,” Salisbury said.

Although mint oil produced in the U.S. is more expensive than oil from Asia, the quality is higher, and consumers want high-quality, natural mint, Salisbury said.

As peppermint growers continue to face challenges in both their fields and their bank accounts, Henry’s research could lead to increased yield while maintaining mint oil quality that could help keep growers afloat in a competitive global industry.

“In a competitive market, this would help us remain very competitive and viable,” said Salisbury. “We can continue to produce the product that everybody knows us for.”