Sun Is Used as Methyl Bromide Substitute

October 18, 1999

USDA researchers are using the sun as a substitute for methyl bromide, a fumigant scheduled to be discontinued in 2005. Last fall, yields from solarized vegetable fields in Florida ranged from 96-123% of yields from methyl bromide-treated fields on three commercial farms.

The process includes covering the soil under plastic for at least six weeks during summer to "cook" weed seeds, diseases and some nematodes. Before the winter crop is planted, the plastic is painted white to cool the soil. The field that yielded 123% 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 sun and heat could destroy them.

Solarization has drawbacks, however. 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 Bermuda grass, all of which are controlled with methyl bromide. Also a grower must get started preparing beds at least six weeks before planting, and that poses logistic problems for larger operations.

Also, solarization requires an integrated pest management (IPM) approach that can include chemicals and changes in cultural practices, depending on which weeds, diseases or insects are in a particular field. Plant pathologist Daniel O. Chellemi of USDA's Agricultural Research Service, says, "Growers are reluctant to adopt IMP to control soil-borne pests; they haven't needed it for 30 years. IPM is a niche that will be filled by other types of professionals," he adds, noting that California now has groups of pest specialists who know the least toxic controls to use for specific pests.

A report on the program is on the Internet at http://www.ars.usda.gov/is/AR/archive/oct99/sun1099.htm.