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Mustard Provides Alternative Pest Control
(Beyond Pesticides, November 30, 2004)
Researchers in Washington State are studying the pest control attributes of mustard, according to the U.S. Agricultural Research Service (ARS). The use of mustard in controlling pests in agriculture entails 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.

ARS reports that interest has been growing on the use of mustard for pest control as well as for “green manure,” meaning it can be disked into soil to improve tilth, organic matter, aeration, and water filtration.
In order to figure out exactly what occurs when mustard is applied to agriculture fields, researchers from a variety of backgrounds are involved in the study. ARS agronomist Rick Boydston, study coordinator since 2000, says, “There's a lot going on there that we don't know about.” Research is needed, for example, to find out conditions under which mustard works best.

ARS states that “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.” The studies going on in Washington are also trying to figure out whether nematodes, weed seeds, or fungi die from direct contact with ITCs or as a result of other chemical or biological changes in soil.

"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."

As summarized on ARS’ website, the following experiments are going on in Washington to examine different aspects of using mustard for pest control in agriculture:

  • Weed-seed bank: Small nylon bags were filled with 500 redroot pigweed seeds and buried at 1 or 8 inches deep. The plots were then overseeded with white mustard, sorghum-sudangrass, winter wheat, or a mix of oat and hairy vetch. Other plots, left fallow, were either fumigated with metam sodium and 1,3-dichloropropene or were not treated.

    In spring, sacks were dug up and the seeds removed and replanted to see whether they'd germinate. "If the seed doesn't sprout, this suggests presence of toxins, such as ITCs, from the cover crop we used," explains Boydston. Citing 2003 results, he adds, "We're not seeing a big effect on buried seed, though we do see a delay in germination."
  • Mustard mulching: This Prosser greenhouse study pits three biofumigant crops (white mustard, brown mustard, and rapeseed) against small-seeded weeds—redroot pigweed and barnyard grass. When mixed into soil, the three mulches cut weed germination by 20 percent to 95 percent. Reductions of 5 percent to 95 percent in growth of seedlings from surviving seeds were also observed.
  • Potted ornamentals: This greenhouse study evaluated the biofumigant effects of crushed seed meal from brown mustard and field pennycress. The targeted pests were chickweed, prickly lettuce, and root-knot nematode.

    First, scientists mixed the seed meal at 0.2 percent to 0.4 percent by weight into potting soil and then planted irises. They then added 100 chickweed seeds, 100 prickly lettuce seeds, and 400 nematodes. As a chemical control, other pots were sprayed with the nematicide ethoprop. At 2, 4, and 6 weeks, they checked the pots for diminished seed germination and sprouting. Nematodes were extracted and counted at the experiment's end.

    In pennycress-treated pots, about 80 percent fewer chickweed seeds and 55 percent fewer prickly lettuce seeds sprouted. Brown mustard seed meal reduced chickweed emergence by 65 percent and prickly lettuce by half. The irises were unaffected. Early results revealed a 70 percent to 80 percent nematode decline in pots containing the seed meals. The scientists are now testing higher seed-meal concentrations and expect to see even fewer nematodes.
  • Crop rotation: Since 2000, the researchers have preceded potato or sweet corn crops with fall-planted cover crops of mustard, winter wheat, sorghum-sudangrass, or oat plus hairy vetch. Another plot, left fallow, is fumigated for comparison. "We have a 4-year rotation in place and are using these covers in 3 of the 4 years," says Boydston. "We hope to detect any cumulative effects of the cover crop's continued use." Throughout, the scientists are monitoring the covers' effects on weed emergence, seedling growth, species distribution, and density.
  • Biomass: Using mustards costs about $90 per acre, notes McGuire. Growers can generally recoup by rotating mustard with a high-return crop like potato. To help them get the most bang for their buck, the researchers are studying the best mustard-seeding time for producing the most biomass, which is thought to be important for many of the crop's benefits.

To find out about more studies ARS is conducting regarding use of mustard as pest control, see http://www.ars.usda.gov/is/AR/archive/oct04/pest1004.htm?pf=1.

TAKE ACTION: Many alternatives to toxic chemicals are available for use in agriculture. Advocate for these alternatives by supporting and buying USDA certified organic products.