Reducing Citrus Fruit Injury From Combination Treatment
of Reduced Methyl Bromide Dose Plus Short Cold Treatment
Laurie G. Houck, Research Plant Pathologist and Joel F. Jenner,
Biological Science Technician; Postharvest Quality and Genetics Research
Unit, USDA, ARS, Fresno, CA 93727.
Treatments developed as alternatives to methyl bromide (MB)
fumigation of postharvest commodities for quarantined insects must address
concerns of fresh fruit injury as well as efficacy on target insect(s).
Although consumers might tolerate certain minor cosmetic injuries to fruit
peel if no other treatments are available, any commodity treatments
causing major blemishes and decay will not be tolerated or used in
commercial institutions even if such treatments are approved by
regulatory agencies.
Currently, we are evaluating an APHIS-approved fruit fly quarantine
treatment using a combination of a reduced MB fumigation dose followed by
a short cold treatment. These treatments use 32g
MB/m3, less
MB than is required when MB is used alone (thereby reducing emissions of
MB from postharvest commodity fumigations), combined with short cold
treatments, shorter and warmer than when cold treatments are used alone.
These short cold treatments used in conjunction with MB are less stringent
than the longer or stand-alone cold treatments and reduce the expensive
time-consuming cold treatments that delay marketing of citrus and increase
fruit senescence and decays.
In several tests completed with lemons and navel oranges, we have
found that aeration after fumigation and before initiation of the cold
treatment is of prime importance. However, an important, and limiting,
requirement of the MB + cold treatment combination is that cold treatment
must be initiated within 24 hours after MB fumigation.
Lemons aerated for the full 24 hours did not develop objectionable
rind injury discoloration or pitting symptoms characteristic of MB injury
and of cold injury (chilling injury; CI). However, sometimes a noticeable
mild peel injury did develop even on lemons a rated the maximum allowed
24 hours. This injury would probably not be a major impediment to
marketing lemons. Injury was more severe on navel oranges than on lemons
and the navel orange injury might not be accepted by consumers. We have
only tested late-season navels, however, and this may not be true for
early-season navels. Injury to both lemons and navel oranges increased
markedly as aeration time was decreased. Injury that developed on fruit
after short aeration times was severe and would not be tolerated.
A full 24-hour aeration would delay marketing of fruit, and
the warm fumigation/aeration temperature required (21oC) could
sometimes lead to an increase in normal rind senescence or injury and
fruit decay in storage/shipping/marketing.
Further tests to evaluate the value of forced shorter aeration times
following MB fumigation to rapidly remove MB from the fruit and cartons
and lessen fruit rind injury will be investigated.
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Last Updated: October 3, 1996
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