Turning to the SunInstead of
Plant pathologist Daniel Chellemi (left) and organic grower Kevin O' Dare
inspect the progress of a soil solarization treatment.
ARS plant pathologist Daniel O.
Chellemi has pulled out all the stops, looking for ways to sustain Southeast
vegetable farmers after the loss of methyl bromide, now slated for the year
2005. Since 1992, his mainstay has been soil "solarization"the
process of heating soil under clear plastic for at least 6 weeks during the
summer to kill off weed seeds and diseases that would otherwise destroy a
Chellemi's efforts are paying off. In 1998, yields from solarized fields
ranged from 96 to 123 percent of those from methyl bromide-treated fields on
three of the four commercial farms cooperating in Chellemi's study. The fourth
farman organic farmdoesn't use methyl bromide or any other
chemicals. The yields have improved over those in earlier years, when Chellemi
collaborated with his former colleagues at the University of Florida at Quincy.
"We're getting better at it," says Chellemi, who is now with ARS'
U.S. Horticultural Research Laboratory in Fort Pierce, Florida. "The more
familiar you become with the biology of the fields, the better the
That's because solarization requires an integrated pest management (IPM)
approach that can include chemicals and changes in cultural practices,
depending on which weeds, diseases, or insects lie waiting in a given field.
Chellemi has been looking at all possible combinations on farms ranging from 10
to 3,000 acres.
The field yielding the 123 percent had been deep-disked before solarization
to break up plant material that had not yet decomposed and to bring tiny,
destructive worms called nematodes to the surface, where the sun and heat could
destroy them. It was planted with peppers.
Another pepper field on the same farm, which had been shallow-disked,
yielded 106 percent as much as a comparable field treated with methyl bromide.
Where no disking was done before solarization, yields were virtually the same
as those achieved with methyl bromide, at 99 percent.
Solarization keeps diseases and blemishes at bay.
On another farm, two solarized pepper fields yielded better than those
treated with methyl bromide118 and 104 percent. Soils in both had been
beefed up with a biosolids compost before planting. It was the second year of
solarization for the field yielding 104 percent and third for the one yielding
118 percent, Chellemi says.
"Although we're not getting the residual benefits from methyl bromide
fumigation anymore, yields are actually going up under soil solarization."
Chellemi suspects that the revival of beneficial microorganismsgiving
the soil a better balanceis behind the increased yields.
Nothing's Ever Quite Perfect
Solarization has its drawbacks: It works only for fall planting, or for half
the crop in the deep South. It doesn't control all pests adequately,
particularly root knot nematodes and the weeds portulaca and
Bermudagrassall of which succumb to methyl bromide. And it requires that
the grower get started preparing beds at least 6 weeks before planting. That
poses logistic problems for the larger operations, says Chellemi.
"Growers are reluctant to adopt IPM to control soilborne pests; they
haven't needed it for 30 years. IPM is a niche that will be filled by other
types of professionals," Chellemi says, noting that California now has
groups of pest specialists who know the least toxic controls to use for
But for organic grower Kevin O'Dare of Vero Beach, Florida, solarization
saved his business. "I can't say enough for it," O'Dare says.
Purple nutsedge was close to taking over the 10 acres of Osceola Organic
Farm, he says, and is even hard to control on conventional farms with
chemicals. Last year, his second year of solarization, "our production was
up 30 percent, our labor was down 75 percent, and our profits were up 100
percent," says O'Dare.
He grows 10 varieties of lettuce, plus tomatoes, peppers, squash, eggplant,
and culinary herbs. At Chellemi's suggestion, O'Dare incorporated compost and
manure into the beds and wet them down before solarizing. "When that mix
heats up under clear plastic, it produces gases, some of which are toxic to
soil pests such as fungi and nematodes and to weed seeds," says O'Dare.
And diseases, which blemish produce, are kept at bay. One of O'Dare's buyers
commented that he "had never seen organic peppers as nice," says
O'Dare. What's more, the covered beds require less water and fertilizer.
"It's a very sustainable system."
A Little Bit of Trial and Error
Dale and Greg Murray of Decatur County, Georgia, are solarizing again this
summer, after a 2-year hiatus. This year, the Murrays have increased their
solarized acreage from 3 to 14 under the guidance of Steve Olson, professor of
horticulture at University of Florida-Quincy, who is a former colleague of
Chellemi. Each season, the brothers grow 100 acres of tomatoes, rotating them
over 400 acres.
During the last study, says Dale, "we had a respectable
yieldencouraging enough to try again. We think we've learned from the
mistakes we made." The two most obvious ones were not burying the
irrigation drip tape deep enough and not covering the clear plastic well enough
with white paint before planting.
As a result, the sun burned holes in the drip tape, and the soil stayed too
hot for the new plants to survive. "A good paint job is essential,"
This year's test field was home to root knot nematodes, so the Murrays
injected a nematocide along with solarizing.
"We'd rather do a little study along the way than lose methyl bromide
and have to do all the trial and error in a year," says Dale. "It's a
big plus to have Dan Chellemi on the farmers' side. He really works to find an
alternative to methyl bromide."
Now in his eighth year of testing soil solarization, Chellemi says,
"There's no doubt in my mind that it has a place. It's not a universal
replacement for methyl bromide, but it is a viable option for farmers who are
willing to explore it.
"We want to tell growers that they're not going to have a widespread
crop failure if they use soil solarization."By
Judy McBride, Agricultural
Research Service Information Staff.
This research is part of Methyl Bromide Alternatives, an ARS National
Program (#308) described on the World Wide Web at
Daniel O. Chellemi is at the USDA-ARS U.S. Horticultural Research
Laboratory, 2001 South Rock Rd., Fort Pierce, FL 34945; phone (561) 462-5800,
fax (561) 468-5668.
"Turning to the SunInstead of Methyl Bromide" was
published in the October 1999
issue of Agricultural Research magazine.