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To Zap Strawberry Foes, Scientists Seek Methyl Bromide Alternatives

By Marcia Wood
November 3, 1999

Root-nibbling microbes, currently held in check by fumigating soil with methyl bromide, might threaten strawberry plants in the future. Most uses of the fumigant--thought to damage Earth's protective ozone layer--will be phased out by 2005.

To help develop alternatives, Agricultural Research Service plant pathologist Frank N. Martin at Salinas, Calif., is scrutinizing these microbial enemies in greenhouse tests and at research plots in commercial strawberry fields along California's central coast. California leads the nation's strawberry production. Strawberry growers are a major user of the chemical.

Martin has been evaluating the abundance and virulence of soil-dwelling microbes called Pythium and Rhizoctonia, which cause a strawberry disease known as black root rot. They also can infect lettuce, tomatoes, cauliflower and many other plants.

Martin's investigation is among the most extensive yet conducted of these microbes in this key strawberry-producing region. The research provides details that better equip scientists to devise new tactics for combating these pests.

Though black root rot doesn't kill strawberry plants outright, it may significantly reduce yields. In the study, severity of plant symptoms varied greatly. Pythium ultimum--the most prevalent Pythium at field sites--and P. irregulare were among the Pythiums causing the most damage to greenhouse plants inoculated with the microbes. But several other Pythium species that were recovered caused few if any symptoms.

All Rhizoctonia forms significantly reduced the growth of greenhouse strawberry plants.

Martin presented his findings at this week's 6th Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reduction in San Diego, Calif. More than 100 other scientific reports from other ARS researchers throughout the U.S., as well as university and industry scientists, are also being given at the conference.

About 330 participants are registered to attend. ARS, USDA's chief scientific agency, is a conference sponsor.

Scientific contact: Frank N. Martin, ARS Crop Improvement and Protection Research Unit, Salinas, Calif., phone (831) 755-2873, fax (831) 755-2814, or at the Methyl Bromide conference through Nov. 4, DoubleTree Hotel, phone (619) 297-5466.