UF/IFAS research harnesses sun's power to kill weeds

November 12, 2009

GAINESVILLE, Fla. — Sunshine helps flowers grow, and it can help rid soil of harmful organisms that hurt Florida’s $9 million cut flower industry, a University of Florida expert says.

In a process called soil solarization, farmers prepare planting beds by covering them with clear plastic sheets for several weeks during the summer, trapping heat that destroys weeds, nematodes and fungi. Popular in California and Israel, solarization is well-suited to Florida’s climate though the practice is seldom used here, said Bob McSorley, a nematology professor with UF’s Institute of Food and Agricultural Sciences.

A study published in the current issue of the International Journal of Pest Management showed solarization effectively prepared planting beds for snapdragons, in some cases as well as the soil fumigant methyl bromide.

“The big challenge is getting (growers) to adopt it,” said McSorley, an author of the study. “They never thought of doing without soil fumigants.”

Soil fumigants are chemicals sprayed or injected into soil to kill pests and pathogens before planting. The best known is methyl bromide, which is being phased out. Federal law now restricts methyl bromide use nationwide; in Florida it’s allowed for a handful of crops including cut flowers, ornamentals, eggplant, pepper, strawberry and tomato. Growers and researchers want cost-effective alternatives.

Solarization has some advantages over fumigants, McSorley said. It’s inexpensive, and it’s environmentally friendly, though the sheeting requires disposal.

The downside is, solarization requires intense sun exposure, so it can only be used during summer, to prepare beds and fields for fall-grown crops. And three to four months after solarization, harmful organisms start to return.

“There are some limitations to it,” he said. “If you want a spring crop you have to use another method in the wintertime.”

McSorley recommends interested growers try solarization on a small plot, and see if it gives the results they need.

One farm that’s taken that first step is Sunshine State Carnations, in Palm City and Hobe Sound. Last year, the Hobe Sound operation took part in a U.S. Department of Agriculture study. It was successful, and this year both locations are using solarization on half-acre plots, said USDA plant pathologist Dan Chellemi.

The study is meant to demonstrate that solarization is practical on a commercial scale, said Chellemi, based at the USDA research laboratory in Fort Pierce. This week, he will give a soil solarization presentation at a conference on methyl bromide alternatives in San Diego.

Overall, he says, solarization has “tremendous potential” for Florida floriculture and vegetable farms, when used as part of an integrated pest management approach. Also known as IPM, this approach emphasizes prevention, monitoring and control of pests with a minimum of pesticides.

Peter Nissen, co-owner of Sunshine State Carnations, says if this year’s study goes well, his company will use solarization on a larger scale, in rotation with soil fumigants.

“We’re trying to save money and help out the environment as well,” he said.

One other group might find solarization helpful: home gardeners.

McSorley plans to publish an extension document in 2010 on solarization for home use.

For more information, see “Solarization for Pest Management in Florida,” http://edis.ifas.ufl.edu/IN824.