ARS Soil Solarization: Fort Pierce, Florida
Florida fresh market tomato and pepper growers account for about 33 percent
of the methyl bromide used for soil fumigation in the United States. Without
methyl bromide, production could potentially decline, unless suitable
alternatives to manage soilborne pests are found.
"For more than 30 years, Florida farmers have used production systems
that rely on the use of a broad spectrum fumigant to disinfest the soil prior to
planting," says Dan O. Chellemi, ARS plant pathologist. "Implementing
biologically based alternatives has been especially challenging to production
systems that use soil fumigants."
Last year, the
ARS
Horticultural Research Laboratory in Orlando hired Chellemi from the
University of Florida to look into this problem at Fort Pierce, Florida. The ARS
Orlando lab is expected to relocate to Fort Pierce in 1999, if lab construction
is completed on schedule. "Our mission is to come up with biologically
based alternatives to methyl bromide," Chellemi says. "To do this, we
must either devise an integrated pest management (IPM) strategy to control
soilborne pests of vegetable crops or we must develop alternative production
systems that minimize the impact of soilborne pests."
Since methyl bromide will no longer be available to growers after January 1,
2001, Chellemi says that in the short term, methyl bromide could be replaced
with another broad spectrum soil fumigant or fumigant/herbicide combination. An
intermediate solution could be an IPM approach that combines multiple tactics
such as chemicals, soil solarization, and cultural practices. And, he says,
production systems designed to minimize outbreaks of potential pests could be a
long-term alternative to soil fumigation.
Over the past 3 years, Chellemi and collaborators from industry and the
University of Florida evaluated soil solarizationalone or combined with
1,3dichloropropene (1,3D), 1,3D and chloropicrin, or municipal
solid waste composton tomato, pepper, cucumber, and pumpkin production.
The research plots were located in several southern and northern Florida
counties, as well as in southern Georgia.
Soil solarization is a hydrothermal process in which clear plastic is
stretched over moistened soil to trap solar energy and heat the soil. Over a 6-
to 8-week period, this procedure can control many of the soilborne pests that
attack Florida's fresh market vegetables.
"Although yields in solarized plots were similar to those in methyl
bromide-fumigated plots, pest control varied among the locations," Chellemi
reports.
Tomatoes
Field plots were established on seven farms located from the southeastern
coast of Florida to southern Georgia, with size ranging from a little more than
an acre to 2.5 acres. Plots were treated with soil solarization, solarization
combined with reduced rates of 1,3D, standard applications of 1,3D
plus chloropicrin, or methyl bromide.
"On three farms, methyl bromide outyielded soil solarization. Yield
with solarization was greater on one farm and yield with 1,3D plus
chloropicirin was greater on one farm," Chellemi reports. "Solarization
suppressed weeds about the same as methyl bromide in all locations except when
purslane and Texas panicum were present."
And, he says, solarization controlled southern blight better than methyl
bromide but was not as good at controlling root-knot nematodes. However,
combining solarization with reduced applications of 1,3D or l,3D
plus chloropicrin achieved nematode control comparable with that of methyl
bromide.
"All tomato growers who participated in this study indicated that they
could use soil solarization in their existing production systems," Chellemi
reports.
Peppers
The experimental plot for peppers consisted of 10 adjacent beds of Myakka
sandy soil covered with 28 tons per acre of a mixture of moist biosolids and
yard waste, 1.1 tons per acre of dried municipal solid waste compost and 733938
pounds of NPK, respectively, per acre. Chellemi and colleagues
covered the beds with clear, 1.2- mil-thick, low-density plastic containing
ultraviolet light inhibitors. They pulled test plants to measure the severity of
root galling by root-knot nematodes and collected soil samples to check for
nematodes. In a nearby control plot, they applied mineral fertilizer to soil
fumigated with methyl bromide and chloropicrin.
Cucumbers
After the last peppers were picked, Chellemi and colleagues mowed the
plants, side dressed the rows with 250 pounds per acre of fertilizer, punched
new holes in the plastic, and planted cucumbers.
In another location, cucumbers were grown as the main crop and three
treatments were used: soil solarization, methyl bromide plus chloropicrin
fumigation, and an untreated control. Again, they evaluated plant roots for
galling and tested soil samples for nematodes. Using drip irrigation, they
injected fertilizer weekly.
Pumpkins
On the pumpkin raised-bed test plots, the researchers used soil solarization
alone, solarization plus 1,3dichloropropene (8 gal per treated acre) and
an untreated control. As with peppers and cucumbers, root gall ratings were
taken for each treatment and soil samples were taken for nematodes.
Results
"In general, we got greater yields from methyl bromide-treated plots
than from the solarized plots," Chellemi reports. "But pest levels
were low in both treatments."
Actual data showed that marketable yield of peppers was 15.3 tons per acre
from solarized plots, compared to 16.4 tons per acre for plots fumigated with
methyl bromide. But suppression of nutsedge and control of nematodes were
similar under both treatments, Chellemi says.
A second crop of cucumbers showed reduced marketable yield, increased
severity of root galling, and more nematodes in solarized beds. In Washington
County, Florida, severe root galling and lots of root-knot nematodes occurred in
untreated and solarized beds, but not in beds treated with soil solarization
plus 1,3D.
In Suwannee County, soil-solarized and methyl bromide-fumigated plots
suppressed yellow and purple nutsedge at about the same rate. Methyl bromide
test plots produced the greatest marketable yield with less root galling and
fewer root-knot nematodes.
"Although research so far shows the performance of soil solarization to
be a little below methyl bromide, indications are that soil solarization can be
incorporated into Florida growers' existing production systems," Chellemi
says. "We've also shown that solarization is cost-effective and compatible
with other pest management systems. We recommend it as a viable alternative to
methyl bromide for fall production systems when used within an IPM program."
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