SAN DIEGO, Oct. 31--Scientists will kick off an international conference here Nov. 2 on the search for substitutes, including harmless natural fungi, to methyl bromide—probably the most widely used pesticide in the world.

Methyl bromide is used to fumigate soil before planting to control plant pathogens and weeds, as a quarantine treatment on harvested crops, as a pest control on stored commodities, and as a structural fumigant. The chemical is slated for ban by the U.S. Environmental Protection Agency on January 1, 2001. The U.S. Clean Air Act requires the ban because methyl bromide has been identified as an ozone depletor.

"The loss of methyl bromide will create potentially devastating problems for agriculture globally," said Kenneth W. Vick, methyl bromide coordinator for the U.S. Department of Agriculture. "Each year at this conference, scientists and industry representatives from around the world discuss their progress on research to find potential replacements for methyl bromide."

Vick leads methyl bromide research at the Agricultural Research Service, USDA's chief scientific research agency. More than 300 participants from 10 countries have registered for the 3-day conference at the Mission Valley DoubleTree Hotel here. More than 122 scientific papers will be presented.

Along with USDA, the Methyl Bromide Alternatives Outreach in Fresno, Calif., is again sponsoring the conference with California's Crop Protection Coalition and the U.S. Environmental Protection Agency.

Potential alternatives to be discussed at the conference include using harmless strains of fungi to control soilborne diseases of tomato, applying natural microbes to fruit surfaces to fight decay-causing organisms and identifying alternative fumigants that don't affect the ozone.

ARS scientists Robert P. Larkin and Deborah R. Fravel are using nonpathogenic strains of the fungus Fusarium to control Fusarium wilt on tomatoes. This disease is now controlled with methyl bromide.

"We've found that it's possible to biologically control this devastating wilt on tomatoes. With further research, these beneficial strains of fungi could potentially control other diseases as well," Larkin said. He and Fravel conduct their research at ARS' Beltsville (Md.) Agricultural Research Center.

Scientists with the ARS Floral and Nursery Plants Research Unit in Beltsville are using natural plant extracts like clove, neem and pepper to control Fusarium wilt of chrysanthemum. The wilt, now controlled with methyl bromide, is one of the most widespread and destructive diseases of this major horticultural crop.

John H. Bowers and James C. Locke of the Beltsville ARS lab will detail their success with plant extracts at the conference. "We're also evaluating other biological agents and cultural practices that might be used in integrated management strategies," Bowers said.

California strawberry growers will be particularly hard hit by the impending ban. They rely almost exclusively on methyl bromide fumigation to control root diseases before transplanting berry plants from the greenhouse to the field.

Frank Martin, with ARS' U.S. Agricultural Research Station in Salinas, Calif., studies the pathogens responsible for yield losses in strawberry fields and investigates the ecology of microbes that colonize roots. This knowledge is needed to develop effective control strategies.

"This research is important not only for information on microbes that decrease yield, but also for identifying beneficial microflora that might improve root health of plants grown in nonfumigated soils," Martin noted. "In growth chamber tests, we've identified several types of bacteria that appear to have either beneficial or detrimental effect on plant growth. We've just completed preliminary field trials to evaluate their effects on plant growth and yield." Martin will report the results at the conference.

Scott Yates, at ARS' U.S. Salinity Laboratory in Riverside, Calif., is reviving interest in propargyl bromide, a chemical used with chloropicrin and methyl bromide in Trizone, a fumigant developed in the 1960s. Propargyl bromide was never commercialized, in part because of the increasing popularity of methyl bromide. The compound is not a currently registered pesticide and its environmental behavior is relatively unknown.

"In our experiments, we found that under typical agricultural conditions, propargyl bromide appears to pose no serious environmental risk," Yates explained. "It degrades quickly in the soil. This would help limit the amount of the chemical that reaches groundwater or escapes into the atmosphere."

At the ARS Subtropical Horticulture Research Station in Miami, Fla., Raymond G. McGuire uses strains of harmless, naturally occurring organisms to reduce postharvest decay in quarantine-treated commodities.

"Heat treatment can predispose certain fruits and vegetables to pathogen attack," McGuire said. "But we've successfully used strains of bacteria and yeast commonly found on fruit to fight decay organisms. These natural organisms can be added to waxes or coatings that are now routinely applied to improve appearance and reduce dehydration."

Scientific contact: Roy Gingery, National Program Staff, USDA, ARS, Double Tree Hotel, Mission Valley, 7450 Hazard Center Drive, San Diego, Calif., Telephone, (619) 297-5466.