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Compost, Mulch and Microbes May Protect Strawberries

By Marcia Wood
March 31, 1999

DAVIS, Calif., March 31--A special compost, a plastic mulch and beneficial microorganisms may be ingredients for the perfect recipe to protect tomorrow's strawberry fields from weeds and soil-borne diseases, Deputy Agriculture Secretary Richard Rominger said last night at an anniversary celebration for the University of California's Small Farm Program.

Scientists with USDA's Agricultural Research Service in Salinas, Calif., are testing the strategy's potential as a replacement for some uses of methyl bromide. This chemical fumigant is being phased out in the U.S. because it is thought to deplete Earth's protective ozone layer.

"The experiments in California are part of USDA's nationwide search for reliable, affordable substitutes for methyl bromide," said Rominger in remarks to an agriculture workshop on the Food Quality Protection Act. "Strawberry growers are major users of the chemical and have relied on it for decades to keep plants free of pathogens–the microorganisms that can cause crop disease."

Strawberry growers fumigate their fields with a mixture of methyl bromide and chloropicrin before planting. That fumigation kills soil-dwelling pathogens, such as those that cause verticillium wilt in strawberries. It also kills weed seeds.

ARS plant pathologist Carolee T. Bull is leading tests of a compost that is enhanced with enzymes, organic acids and beneficial bacteria. The compost is combined with corn gluten meal and beneficial fungi. She is doing the work at commercial strawberry fields and research plots in central California.

"The enzymes," said Bull, "should speed decomposition of the compost, making nutrients available to beneficial microbes that we have applied to the fields.

"The beneficial bacteria that we are investigating may stimulate the plants' defenses against pathogens," she continued. "The fungi--known as mycorrhizae--help plants take up water and phosphorus from the soil." The experiments will also determine whether weeds are quelled by beneficial microbes and corn gluten meal, a corn processing byproduct.

In strawberry test plots, Bull and colleagues will compare size and health of plants grown using the new strategy to plants fumigated with either methyl bromide or methyl bromide plus chloropicrin.

The tests are part of a cooperative research and development agreement between ARS and Soil Technology, Fallbrook, Calif.

The average American eats about five pounds of strawberries per year. Strawberries are fat-free, low in calories and a source of vitamin C, folic acid, potassium and fiber. The fruit also is high in antioxidants that may protect cells from damage.

California is this country's top strawberry producer. The nation's 1998 strawberry crop of 869,350 tons was worth more than $1 billion to growers.

Other ARS efforts to find methyl bromide alternatives include:

Scientific contact: Carolee T. Bull, ARS Crop Improvement and Protection Research Unit, Salinas, Calif., phone (831) 755-2889, fax (831) 755-2814,