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Controlled Atmospheres + Heat = A Methyl Bromide
Replacement?
No one is sure that Joseph in Biblical times did not use controlled
atmospheres to preserve the grain that kept starvation at bay during the 7
years of famine that followed the 7 years of plentiful harvests in Egypt.
But it is a fact that, in ancient times, grain was stored in underground
pits, which still exist in arid parts of the Middle East. Low oxygen
levels in these pits kill pests, constituting a somewhat controlled
atmosphere.
Although not quite that long ago, but for more than 30 years, ARS scientists have been studying the
effects of controlled atmospheres on insect pests in stored grain. By
modifying levels of oxygen, nitrogen, and carbon dioxide, they have been
able to control these pests. Normal, or ambient, air composition is 78
percent nitrogen, 21 percent oxygen, and 0.033 percent carbon dioxide. Any
significant deviation from this composition results in a modified, or
controlled, atmosphere.
"As a result of 15 years of ARS research, in 1981 EPA approved
controlled atmospheres as a means to manage insects infesting dried fruits
and tree nuts," says Edwin Soderstrom, an ARS research entomologist.
Soderstrom began his work on controlled atmospheres in the 1970's at the
ARS Horticultural Crops Research Laboratory in Fresno, California.
Research by scientists at ARS laboratories in Manhattan, Kansas and Savannah,
Georgia, helped gain the EPA approval.
By adding or removing gases as needed, scientists have also developed
modified atmosphere treatments that kill pests in fresh horticultural
products. Although research using controlled atmospheres to manage
insects on fresh produce has been ongoing for some time, there has been
little commercial application of these treatments. Controlled atmospheres
are successfully used in long-term storage of apples and several other
fruits and vegetables. However, these treatments are not well tolerated by
some horticultural commodities.
Some horticultural commodities, like cherries, must be free of insects
of quarantine concern to the importing country. Japan, for instance,
requires a methyl bromide treatment for fresh U.S. cherries entering
Japan. This is to ensure that the codling moth (Cydia pomonella),
a common pest of apples in Europe and North America, does not enter and
become established in Japan.
"We shipped about 1.4 million boxes of sweet cherries to Japan in
1995, which is 27.3 percent of the total crop from California, Oregon, and
Washington, the major U.S. cherry producing tates," says Lisa G.
Neven, a research entomologist at the ARS Yakima Agricultural Research
Laboratory in Wapato, Washington. "Under current Japanese
regulations, if acceptable alternatives are not developed, this market
will be lost when methyl bromide is banned in 2001."
Neven has collaborated with Elizabeth J. Mitcham, a postharvest
pomologist with the University of California at Davis, on an alternative
treatment using controlled atmospheres and heat.
"We combined controlled atmosphere with high temperatures and
came up with a treatment that kills codling moth larvae in sweet
cherries," Neven reports.
Temperature had been studied as a potential quarantine treatment for
pests in temperate fruits, she says, and controlled atmospheres had been
used for insect control in a few fresh commodities. However, it was not
known if fruit could tolerate exposure to high temperatures under
controlled atmospheres.
For their research to combine high temperatures with a controlled
atmosphere, Neven and Mitcham designed unique quarantine chambers called
CATTS (Controlled Atmosphere/Temperature Treatment System). These research
chambers were built by Techni-Systems of Chelan, Washington, at the ARS
Yakima lab and at the University of
California-Davis. The unit controls temperature, humidity, and
airspeed and differs from other hot-air treatment chambers in that it also
controls atmospheric gases. Initial results with fruit were promising.
This past season, Neven cooperated with Steve Drake (ARS-Wenatchee, Washington). They
subjected high-quality, fresh sweet cherries to 115 oF to
117 oF--with
oxygen levels at 1.0 percent and carbon dioxide, 15 percent--for 60 and 25
minutes, respectively, without affecting the quality. Up to 2 weeks after
treatment, there were still no undesirable changes in acidity, soluble
solids, or firmness of the fruit.
"Our results show that using a combined treatment of a controlled
atmosphere along with heat resulted in more codling moth deaths than heat
alone," Neven says. "Also, we found that the total length and
intensity of a heat treatment can be dramatically reduced by using a
controlled atmosphere."
Because this treatment is so different from methyl bromide, it is hard
to make a comparison, but she says that it is in the ballpark for insect
mortality levels required for a quarantine treatment. Neven plans to try
the treatment on an industrial scale with scientists at Washington State
University in the fall of 1996 to test its potential as a nonchemical
quarantine treatment for sweet cherries that could replace methyl bromide.
[April 1996 Table of Contents]
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Last Updated: October 15, 1996
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