Sulfuryl Fluoride: The Postharvest Fumigant of the Future?
Sulfuryl Fluoride: The Postharvest Fumigant of the
Future?
Sulfuryl fluoride is considered by many to be the postharvest fumigant of
the future, replacing the soon-to-be-eliminated methyl bromide. Under the trade
name Vikane gas fumigant, it is currently registered for structural fumigations
to combat wood termites and wood-boring beetles.
Dow AgroSciences has begun
EPA registration procedures to allow its use
in postharvest situations.
Unlike methyl bromide, which is being phased out because it was determined
to be an ozone depleting substance, sulfuryl fluoride is not an ozone depleter.
Dow AgroSciences is pursuing the registration of sulfuryl fluoride as a gas
fumigant for postharvest use in dry fruits, tree nuts, and cereal grains. The
postharvest formulation of sulfuryl fluoride will be called ProFume gas
fumigant. Tolerance testing is currently under way on each of the food types,
with the ultimate goal of phasing in the use of ProFume as methyl bromide is
being phased out. According to Brian Schneider, Dow AgroSciences' ProFume
biology development leader, this should be an accomplishable goal. "We
have a jump-start since sulfuryl fluoride is already registered for structural
uses," contends Schneider.
In structural fumigation, methyl bromide and sulfuryl fluoride are applied
in a similar manner, and confinement procedures must be strictly adhered to for
both. Schneider says sulfuryl fluoride penetrates organic substrates better
than methyl bromide. "Because sulfuryl fluoride is an inorganic material,
as opposed to the organic methyl bromide, it doesn't bind onto items being
protected, so more of the chemical is available to get to the insects,"
says Schneider.
Sulfuryl fluoride is very effective against the active life stages of
postharvest insects, according to ARS entomologist J. Larry Zettler of the
Horticultural
Crops Research Laboratory in Fresno, California. But sulfuryl fluoride
requires more fumigant for egg stages than for other postembryonic stages.
"But increasing exposure time or temperature may increase the chemical's
effectiveness on eggs," comments Zettler.
In studies Zettler conducted with colleague Richard F. Gill, lab-reared
codling moths and navel orangeworms were exposed to vacuum-chamber fumigation
of a little more than an ounce of sulfuryl fluoride per cubic meter of air. The
dose and length of exposure resulted in total insect kill. Codling moths and
navel orangeworms are established pests of walnuts. "It has great
potential as a tool in postharvest fumigation," says Zettler.
The dried fruit and nuts industry is excited about the results so far. Mike
Hurley, laboratory director of the Dried Fruit and Tree Nut Association of
California, feels sulfuryl fluoride will prove helpful. "Though not as
effective as methyl bromide, sulfuryl fluoride is in the lead as an
alternative."
Toxicity is an ever-present issue that Dow AgroSciences will address in
EPA-mandated toxicity tests. According to Hurley, "sulfuryl fluoride
leaves no parent compound residue on foods," meaning less chemical
exposure to consumers. Fluoride residues in food commodities may be increased,
however, with levels dependent on the type of commodity and fumigant dosage.
Toxicity is only one feature of sulfuryl fluoride that Dow AgroSciences is
committed to understanding. Dow AgroSciences is looking at ways to achieve
optimal fumigation efficiency employing more efficient gas introduction
procedures, improved sealing techniques, use of heat to increase
susceptibility, and gas monitoring during exposure. They are also working with
industry, university, and ARS researchers to help understand insect pest
infestation action levels and economic thresholds to provide guidance to
fumigators on treatment timing and the most economical dosages.
Pest population rebound is a significant issue for all postharvest
fumigants. Several variables are involved in population rebound including gas
concentration in the building, immigration, and temperature. Dow AgroSciences
is looking at ways to bring about peak fumigation efficiency. Maintaining
adequate gas concentration throughout the building to produce insect kill is
crucial in that equation. Currently, Dow AgroSciences is also conducting
modeling studies of insect population rebound after fumigation in mills and
processing plants. This work complements similar research being conducted by
Jim Campbell at ARS, Manhattan, Kansas, in feed mills fumigated with methyl
bromide.
Though sulfuryl fluoride must undergo rigorous EPA registration procedures,
its approval will provide an acceptable alternative to methyl bromide, thus
filling a substantial need for postharvest fumigants.
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Last Updated: November 22, 2000
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