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Florida Focus
November 2009
Let the sun shine in on soil-borne pests with solarization
By Vicky Boyd, Editor
With methyl bromide growing more scarce and expensive, soil solarization may be an option growers want to incorporate into an integrated pest management program, says a University of Florida nematologist.
The technique harnesses the sun’s heat to cook the soil, killing soil-borne pests in the process, says Bob McSorley, a nematology professor with the Institute of Food and Agricultural Sciences in Gainesville.
Soil solarization is ideally suited to Florida because the time when the sun’s rays are the most intense—summer—also is the time when most crops are out of the ground and fields sit vacant, he says.
McSorley and Dan Chellemi, a U.S. Department of Agriculture research plant pathologist in Fort Pierce, have studied solarization as a way to reduce soil-borne pests since 1989.
Back then, growers mostly overlooked the technique since methyl bromide was inexpensive and readily available. But McSorley says the methyl bromide phase-out has caused some growers to take a second look.
Soil solarization involves putting clear plastic over the soil for at least six weeks during the summer. For best results, the sun’s rays need to heat the soil to 110 degrees Fahrenheit 3 inches deep or 100 degrees 6 inches deep.
The effects last for three to four months before they begin to wear off.
Results are similar whether you’re in Quincy or in south Florida, he says.
“The shorter the crop, the better it will work,” McSorley says. “If you want to grow something that lasts eight or nine months, then you’ll start to see problems.”
The same holds true if you want to double-crop on solarized land. You probably will see a break-down in soil-borne pest control with the second crop.
The effects of methyl bromide, on the other hand, will last seven to eight months and penetrate about 1 foot deep, he says.
The thickness of the plastic isn’t all that important, McSorley says. What is crucial is that it is clear so you get the maximum solar penetration.
“We have done [trials] with various thicknesses, and as long as it’s completely clear, it works. It can’t be translucent,” he says.
The plastic also needs to be durable to hold up during the summer’s heat, so it can be easily removed after treatment.
After removal, growers return and apply their typical plastic bed mulch, whether it be reflective or colored, for the growing season.
Like most other pest-control options, McSorley says soil solarization should not be viewed as a stand-alone treatment.
Instead, it should be part of an integrated approach that may include other soil fumigants, pest-resistance plant varieties, cover crops and other cultural practices.
For more information, visit "Solarization for Pest Management in Florida.".
