Walnut Pests Foiled by Fumigant, Studies
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
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'
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:
Scientific contact: J. Larry Zettler and James G. Leesch, ARS
Horticultural Crops Research Laboratory, Fresno, Calif., phone (559) 453-3000,
fax (559) 453-3088, firstname.lastname@example.org or