|
|
Managing Stored Grain Insects in Fall and Winter
Bill Wilcke, Minnesota Extension
Engineer
Colleen Cannon, Minnesota Extension Entomologist
We tend to get the most questions about problems with insects in stored
grain in late summer and early fall. Problems are most common during
warm weather in grain that has been held over from the previous year.
Farmers discover the insects when they get ready to move grain or to
prepare bins for harvest of the new crop. What causes insect problems,
what can be done about them, and how can they be prevented in the future?
- The primary factor for development of stored grain insects is grain
temperature. When grain temperature is between about 60º and
90ºF, insects grow and reproduce rapidly. If grain temperature
can be kept below 60ºF, insects develop slowly, or not at all.
In the upper Midwest, it’s relatively easy to aerate grain to
keep it below 60ºF in fall and winter, but it’s a challenge
during summer months—which is probably why we see more problems
at the end of summer. Other factors that can contribute to stored
grain insect problems are:
- The presence of insect populations in or near the bin at the time
the new crop is added. Some stored grain insects don’t fly very
well or very far, and often many of the insects that enter new crop
grain come from the old grain and dust in the grain storage and handling
facility.
- Broken grain kernels and other fine material in the grain. Fine
material is a problem because some insect species can only feed on
broken kernels and because fine material tends to accumulate in concentrated
areas that are difficult to aerate.
The presence of moldy grain in the bin. Some insects actually feed
on mold, but also, mold growth produces hot spots that attract insects.
Considering that warm grain temperatures, initial presence of insects
in the bin, fines, and moldy grain all contribute to insect problems
in stored grain, the best strategies for managing insects include:
- Cleaning bins and handling equipment thoroughly before harvest to
remove the old grain, grain residue, and dust that can be the source
of insect infestation.
- Cleaning grain before storage to remove broken kernels and other
fines, or at least filling bins in a way that minimizes concentration
of fines under the bin fill spout (this includes using grain spreaders
to distribute fines more evenly, moving the fill spout frequently
during bin filling, or withdrawing some grain from the bin through
the center unloading sump during bin filling to remove fines that
accumulate in the center of the bin).
- Making sure that stored grain is dry enough so that it won’t
mold (13% moisture for small grains; 15% moisture for corn stored
through the winter, 14% for corn stored through summer, and 13% for
corn stored more than one year).
Aerating grain as needed during cool weather to keep grain temperature
at 20º to 30ºF during winter months and 50ºF or less
during other times of the year.
There are several insecticides that are registered for treatment of
empty bins and some that are registered for use on stored grain, but
before buying insecticides, compare the cost for insecticide treatment
compared to other insect management options and make sure that potential
buyers will accept grain that has been treated with an insecticide.
What can be done if insects are discovered in stored grain in late
summer? Farmers who have livestock could try to feed the grain as rapidly
as possible before the problem gets too bad. Farmers who don’t
have livestock could consider selling the grain to a neighbor who feeds
livestock. It is important, though, to be honest with the neighbor about
the fact that the grain contains insects and to be prepared to accept
a reduced price for the grain.
In cases where the plan is to sell old crop grain before the new crop
is harvested, or where the plan is to keep old crop grain through winter,
running the grain through a grain cleaner to remove broken kernels and
some of the insects could reduce insect populations and improve grain
storability. Cleaning the grain won’t remove all the insects, but
it might reduce populations enough to allow sale of the grain, or at
least to buy some time for other insect management options.
If average outdoor temperatures are well above 60ºF and weather
below 60ºF is not expected for some time, consider fumigating the
grain. But use grain fumigation only as a last resort. Grain fumigation
is costly, the chemicals used for grain fumigation are potentially hazardous
to human health, and special licenses, equipment, and procedures are
needed to apply fumigants. Also, since grain fumigants do not provide
any residual protection against insects, fumigation is only a temporary
control measure. If the insect problem developed because the grain is
warm, moldy, or contains fines, insect populations will build up again
soon after the fumigant dissipates.
If insect problems are discovered at a time of the year when outdoor
temperatures dip below 60ºF at least part of the day, run aeration
fans during the coolest parts of the day - even if that’s just
at night, to cool the grain. Keep track of grain temperatures and insect
activity and operate the fans as needed to cool the grain to around
40ºF during fall. If the grain will be stored through winter, aerate
the grain again as the weather gets colder to reduce the grain temperature
even further. Most insects go dormant at around 40ºF and many will
die if they are held at low temperatures for long periods of time. The
lower the temperature, the faster insects will die. If grain is cooled
to well under 30ºF, it might be a good idea to aerate grain again
in late winter to bring its temperature back up to 30º to 40ºF
to avoid excessive temperature differences between the inside and outside
of the bin during warm spring weather.
The time required to cool a bin of grain depends on the airflow per
bushel that can be provided by the fan. A rough estimate of the number
of hours that a fan needs to operate to cool a bin of grain can be found
by dividing the number 15 by the airflow delivered by the fan expressed
in cubic feet per minute per bushel of grain in the bin (15 divided
by cfm/bu). Many storage bins are equipped with fans that can provide
0.1 cfm/bu, which means that about 150 hours (15 divided by 0.1) of
fan operation are required to completely cool the grain in those bins.
Long-term weather records for southern Minnesota indicate that, on average,
there are about 100 hours when the outdoor temperature is below 60ºF
during the month of August, 150 hours when the temperature is below
50ºF in September, 200 hours when the temperature is below 40ºF
in October, and 350 hours when the temperature is below 30ºF in
November. This information can be useful for deciding what fan size
might be appropriate for a desired aeration management strategy and
can indicate what grain temperatures might be achievable with an existing
fan.
For more information about managing stored grain and selecting fans
see Resources.
|