Gregory Johnson
Montana State University Extension Service
This
MontGuide explains procedures for proper winter storage and
handling of leftover liquid pesticides. Freezing of liquid
pesticides can result in separation of the active ingredient
from the solvents or emulsifiers, or inactivation of emulsifiers,
which may lead to crystallization or coagulation of the pesticide.
Applicators should know which pesticides can be frozen and
which cannot. Techniques for thawing and redissolving are
also important since a pesticide, once frozen, can plug spra
equipment, result in poor product performance and/or damage
crops if the proper thawing and mixing procedures are not
followed.
The
cold weather storage information in this MontGuide was compiled
from information obtained from manufacturers of the pesticides
listed. Each manufacturer was sent a list of questions regarding
correct storage methods for their pesticide(s) during sub-zero
weather. The questions asked were:
- Does
the product have a minimum storage temperature?
- Should
freezing of the product be avoided?
- If
frozen, will the active ingredient separate from the inert
carriers?
- Once
thawed, will the active and inert ingredients go back into
suspension?
- Is
agitation recommended before the product will go back into
suspension?
- Is
the effectiveness of the pesticide reduced if frozen?
- Are
heated or well-insulated storage facilities recommended?
- Should
the pesticide applicator contact the manufacturer if the
pesticide freezes?
Based
on manufacturers' responses, many pesticides can freeze with
no adverse effects to the pesticide, although separation of
the active ingredient and solvent will occur. Certain steps
must be followed before using a pesticide that has been frozen.
First, the product must be thawed. Before attempting to thaw
a frozen pesticide, however, the container should be checked
to make sure that it is not ruptured or cracked from the expansion
of the frozen liquid. If sound, the container should b brought
to room temperature (placed in a heated room or the south
side of a sunny building away from children, livestock and
pets) for the thawing process, which may take several days.
Once the liquid has thawed, the container can be rolled, shaken
or otherwise agitated to get the contents into a uniform suspension.
The container should also be inverted several times to ensure
the product is completely dissolved. Pesticide manufacturers
caution that if a pesticide cannot be totally redissolved
(crystals are still present), the pesticide should not be
used.
In
the following table, minimum storage temperature refers to the
temperature required to keep the pesticide in solution. Below
that temperature, the pesticide will form crystals and freeze.
The freezing point of many pesticides is lower than 32°F
due to the hydrocarbon solvents or inert ingredients. Pesticides
that cannot be frozen should be placed in a heated or adequately
insulated area to avoid sub-zero temperatures.
Wettable
powders and granules, as a rule, are not affected by low temperatures.
These formulations should be stored in a dry place as moisture
may promote caking or lead to certain chemical changes that
reduce their effectiveness. Products formulated in water-soluble
bags require special winter storage. These bags have a high
affinity for moisture and become brittle when frozen. If handled
when brittle, they will break open. It is important that they
be stored in heated facilities.
Before
storing pesticides for the winter, the applicator needs to
read the pesticide label. While extreme care was taken to
assure the accuracy of the information in this MontGuide,
labels continue to beamended. Therefore, they should always
be consulted.
Disclaimer
and Reproduction Information: Information in NASD does not
represent NIOSH policy. Information included in NASD appears
by permission of the author and/or copyright holder. More
NASD Review: 04/2002
This
document is
MT 8706
,
a series of the Montana State University Extension. Publication
date: September 1987.
Gregory
Johnson, Pesticide Education Specialist. Montana State University
Extension, Bozeman, Montana 59717.
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