Though Idaho may be known for its potatoes, the state exceeds most any other for a much lesser-known crop: peppermint. But across the U.S., mint farmers see a major threat to production that’s prompting them to find another business.
Tiny worms in the past decade have been spreading a deadly fungal disease that’s wreaking havoc on Idaho mint — a $21 million industry and the second-highest in the U.S., according to the U.S. Department of Agriculture.
Lower mint prices and an increase in microscopic worms that worsen the fungal disease, known as Verticillium wilt, have resulted in a $4 million drop in Idaho peppermint sales last year, according to the USDA. Farmers harvested 12,300 acres of peppermint that same year, which is mostly used to make oil sold to flavor products, the federal agency said.
Joe Weitz, the owner of Western Farms Inc. in Caldwell, Idaho, thinks the outlook for this year might not be much better.
Western Farms Inc. in Caldwell, Idaho, seven years ago harvested around 1,000 acres of mint, but this growing season, they are down to about 400, Weitz said.
“It can be difficult and expensive to keep growing mint after the first couple of years,” Weitz told the Idaho Statesman.
Mint can be challenging to produce; it grows well on new land, but when diseases settle in, production takes a hit, Weitz said. Once Verticillium wilt infected mint populations in the Midwest decades ago, farmers moved to land where the pathogen isn’t present, which is why most mint is now grown in the Pacific Northwest, Weitz said.
Verticillium wilt, which causes wilting leaves, stunted growth and plant death, is now widely spread in Idaho, Weitz said.
The fungus is made worse by nematode infections that are getting worse in Idaho, explained Saad Hafez, a professor in plant pathology at the University of Idaho. Lesion nematodes cause destructive damage to a mint plant, and spread fungus within and between plants. While pin nematodes feed on and weaken plant roots, making them more susceptible to Verticillium wilt infections.
“Fungus and nematodes almost always come together,” Hafez told the Statesman.
The nematodes also contaminate equipment and spread by wind and irrigation water, Hafez said, meaning they can move from acre to acre or even farm to farm. Once they are introduced to an area, it can be almost impossible to get rid of them or keep them from spreading, he said.
Treating mint pathogens is hard and expensive
Hafez and Weitz agree that while fungi and nematodes can be treated, it’s not cheap, and nothing lasts or solves the problem.
Fumigation, typically done once the mint is removed from the land or before planting, can cost $500 to $600 an acre, Weitz told the Statesman.
Chemical management that can be applied during the growing season can cost up to $3,000 an acre, and while there are chemical treatment options for nematodes, there is not much on the market to treat Verticillium wilt, Hafez said. But regardless of treatment, mint growth drops every year once Verticillium wilt is introduced Hafez explained.
At Western Farms, in acres where the costs have outweighed the benefits for mint growth because of Verticillium wilt, they have rotated in crops like corn and onions while they wait for the fungi to die down — which can take decades.
The best way to protect mint crops is to prevent nematode and Verticillium wilt infections by buying clean crops and sterilizing equipment and soil, Hafez said, although he acknowledges prevention is difficult.
