By Tom Burfield
Growers are finding they can cut costs, preserve the environment and even boost yields by using plant-based biofumigants rather than conventional fumigants like methyl bromide to control soilborne pests in fields.
The most commonly used biofumigants are members of the Brassica family, and mustard species in particular. They contain glucosinolates— compounds that makes some mustards hot—that can be deadly to weeds, soilborne pathogens and nematodes, says Mark Uchanski, assistant professor of vegetable physiology at New Mexico State University in Las Cruces.
When Brassicas are disked, cells are broken and release glucosinolates. They combine with a naturally occurring enzyme and water, producing a fumigant that’s similar to metam sodium.
Not only are biofumigants a more economical, safer way to control pests, but Uchanski says that plowing the plants into the ground leads to increased soil organic matter, which can result in better yields and larger, healthier plants.
Jack Brown, professor of breeding and genetics at the University of Idaho in Moscow, views the plant-based system’s safe environmental profile as its strong suit.
“[Biofumigants] are natural products that don’t pose a risk to the environment, and they don’t pose a health risk to the people who use them,” he says.
But the plant-based system carries its own set of challenges, including additional management and water requirements, timing of incorporation, and mixed results, depending on the soil pest spectrum.
How effective biofumigants are depends on where you farm, says Sieg Snapp, associate professor and soils and cropping system ecologist at Michigan State University’s W. K. Kellogg Biological Station in East Lansing.
Michigan has a short production window, since the weather has to be warm enough to grow the mustards, she says. You don’t want them to interfere with your cash crops.
After winter wheat is a good time to plant mustards, she says. Or in the spring, before planting late-sesaon vegetables, such as snap beans.
“The soil has to warm up enough to grow your cover crop,” she says.
But like others who work with biofumigants, Snapp advises allowing plenty of time between the biofumigant crop and planting your cash crop.
“It’s important to get some incorporation of the biofumigant in time for it to decompose,” she says. “You certainly don’t want to kill your crop.” Small-seeded crops, such as lettuce and carrots, are most vulnerable, so allow about three weeks to be safe, she says. For large-seeded crops, including potatoes, one or two weeks may be sufficient.