United States Department
of Agriculture (USDA), Agricultural Research Service
Fluoride: The Postharvest Fumigant of the Future?
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
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.
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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