Daily News Archive
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
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
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,
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