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Walnut Pests Foiled by Fumigant, Studies Show / November 5, 1999 / News from the USDA Agricultural Research Service

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Walnut Pests Foiled by Fumigant, Studies Show

By Marcia Wood
November 5, 1999

Freshly harvested, American-grown walnuts may be able to meet European Union import standards throughout the new century, despite the impending withdrawal of the methyl bromide fumigant today used to keep the nuts pest free.

Scientists with USDA's Agricultural Research Service in Fresno, Calif., have shown that fumigating the nuts--still in the shell--with an alternative chemical, sulfuryl fluoride, kills any live codling moths or navel orangeworms in their worm-like, larval stage. That's the only life stage that could hitchhike on harvested walnuts.

The scientists are the first to show the potential of sulfuryl fluoride as a methyl bromide alternative for fumigating walnuts. They reported the findings this week in San Diego at the 6th Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reduction.

EU nations--key importers of American walnuts--currently require methyl bromide fumigation. However, the chemical is scheduled for phase-out by 2005 because of evidence it contributes to depletion of Earth's protective ozone layer.

Sulfuryl fluoride is not an ozone depleter. While approved as a structural fumigant, it would still have to be registered for food uses.

In studies, ARS researchers J. Larry Zettler and Richard F. Gill found that exposing lab-reared moths and orangeworms to vacuum-chamber fumigation of slightly more than one ounce of sulfuryl fluoride per liter of air kills these insects. Preliminary fumigation experiments by ARS colleague James G. Leesch, using some 2,500 walnuts artificially infested with codling moths in their wormlike larval stage, indicated that using seven times less sulfuryl fluoride than methyl bromide killed 100 % of the codling moth larvae. The scientists are based at ARS' Horticultural Crops Research Laboratory at Fresno. The Walnut Marketing Board helped fund the research.

ARS is a sponsor of the methyl bromide conference. ARS' Methyl Bromide Alternatives Newsletter gives details about other efforts at the agency and elsewhere to find alternatives to the compound, which has numerous agricultural uses. The newsletter is on the web at:

http://www.ars.usda.gov/is/np/mba/mebrhp.htm

Scientific contact: J. Larry Zettler and James G. Leesch, ARS Horticultural Crops Research Laboratory, Fresno, Calif., phone (559) 453-3000, fax (559) 453-3088, lzettler@qnis.net or jleesch@qnis.net.

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