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 solarization—alone or combined with 1,3–dichloropropene (1,3–D), 1,3–D and chloropicrin, or municipal solid waste compost—on 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 1,3–D, standard applications of 1,3–D plus chloropicrin, or methyl bromide.

"On three farms, methyl bromide outyielded soil solarization. Yield with solarization was greater on one farm and yield with 1,3–D 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 1,3–D or l,3–D 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 73–39–38 pounds of N–P–K, 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 1,3–dichloropropene (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 1,3–D.

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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Last Updated: April 22, 1998