Mustard for Pest Control, Not for Your Sandwich
A cover crop of mustard like
the one shown above can be
disked into soil as "green
manure" to act as a natural
fumigant for weeds and
Got nematode troubles? Fungi? Too many weeds in a field? Spread some mustard on 'em.
Agricultural Research Service and university scientists are experimenting with mustards as an alternative to chemically fighting crop pests.
But scientists aren't smearing pests with mustard that comes in a jar. Rather, they're biofumigating pests with stands of white mustard, brown mustard, and rapeseed—members of the Brassica plant family. "Biofumigation" refers to natural substances plants release while decomposing that make surrounding soils toxic to some weeds, nematodes, and fungi.
The experiments, in Washington State, dovetail with increasing grower interest in mustard crops for pest control and as "green manure"—meaning it can be disked into soil to improve tilth, organic matter, aeration, and water filtration.
Despite such benefits, there's still much to learn about how mustards control pests and under what conditions they work best, notes ARS agronomist Rick Boydston, study coordinator since 2000.
In autumn, technician Dallas
Spellman buries nylon packets
containing weed seeds to
evaluate their survival
with various fall-planted
Much credit for mustard's biofumigant effect against soilborne pests is given to isothiocyanates (ITCs), chemical byproducts of the plants' decomposition. But scientists suspect ITCs are only one piece of the pest-control puzzle.
"There's a lot going on there that we don't know about," says Boydston, at ARS's Vegetable and Forage Research Unit, Prosser, Washington. A chief question is whether nematodes, weed seeds, or fungi die from direct contact with ITCs or as a result of other chemical or biological changes in soil.
To find out, Boydston is collaborating with the multidisciplinary team of Ashok Alva, a soil scientist who leads the Prosser lab; Harold Collins, an ARS microbiologist there; Steve Vaughan, a chemist at ARS's National Center for Agricultural Utilization Research, Peoria, Illinois; Ekaterini Riga, a nematologist at Washington State University (WSU) in Prosser; and Andy McGuire, an agricultural systems educator with WSU's Center for Sustaining Agriculture and Natural Resources, in Ephrata.
With such wide-ranging expertise, the team can examine many facets of mustard cover crops that growers have neither the time nor resources for.
Microbiologist Harold Collins
evaluates soil bacterial diversity
under various cover crop treatments.
"Growers are probably more focused on nematode suppression and wind erosion control. But our group can measure disease incidence, nematodes, weeds, and soil microorganisms," he says. "We're looking at multiple problems and benefits."
The resulting information could lead to new cropping systems that use mustards better—or pinpoint their limitations. Another possible spinoff could be development of new mustard cultivars custom-bred for specific uses, such as anchoring soil or biofumigating it.
The following experiments are under way at several Washington locations:
Agronomist Rick Boydston and
microbiologist Harold Collins
record weed density in potatoes
after cover crop treatments.
They also want to determine the best time to disk mustard into the soil to unleash its biofumigants. Current thinking is that disking live, green mustard will trigger the greatest release of glucosinolates, which break down into ITCs. But other compounds or soil factors may contribute as much as or more than ITCs to suppressing weeds and diseases. To find out, researchers are comparing weed densities after mustard is disked into the soil in fall while it is still alive and in spring after it has died.
In still other studies, Collins is looking at how microbial soil communities may change in response to mustards and their decomposition. He and Alva are also using isotopes of nitrogen to trace how much of this nutrient mustard returns to soil for other crops to use.
McGuire evaluates various mustard cultivars, including some from Italy and Germany, for their ease of growth, flowering times, biomass, and glucosinolates. Meanwhile, WSU colleague James Dobrowolski is testing wind-erosion resistance of mustard-amended soil by blasting it with gusts from a wind machine.—By Jan Suszkiw, Agricultural Research Service Information Staff.
This research is part of Integrated Farming Systems, an ARS National Program (#207) described on the World Wide Web at www.nps.ars.usda.gov.
"Mustard for Pest Control, Not for Your Sandwich" was published in the October 2004 issue of Agricultural Research magazine.