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One More Reason to Clean Corn Before Storage
Bill Wilcke, Minnesota Extension
Engineer
Vance Morey, Professor, University of Minnesota
Nalladurai Kaliyan, University of Minnesota Biosystems and Agricultural
Engineering Department
Colleen Cannon, University of Minnesota Entomology Department
Mario Carrillo, University of Minnesota Entomology Department
We’ve always recommended cleaning grain before storage to help
keep stored-grain insects under control, but now we have additional
data to support that recommendation. In a study conducted by the University
of Minnesota Biosystems and Agricultural Engineering Department and
the University of Minnesota Entomology Department, graduate students
assessed the survivability of Indian meal moth larvae (the immature
stage of the insect that feeds on grain kernels) on diets that contained
100% whole corn kernels, whole kernels mixed with 5 to 7% broken kernels,
and 100% broken kernels. The study was conducted on small samples of
corn kept at room temperature in an entomology laboratory.
We know that a certain percentage of every generation of insects will
die due to natural causes. However, the more favorable the environment
and the better the food source, the greater the percentage of insects
that survive. In a test using conventional yellow dent shelled corn,
80% of the insects survived on the diet in which all the kernels were
broken and 61% survived on a diet that contained 7% broken kernels,
but only about 7% survived on a diet that contained only whole (unbroken)
kernels. These results indicate that if you clean corn to remove broken
kernels before the corn is stored, that it will be much less likely
that stored-grain insects like Indian meal moth will become a problem
in the storage bin.
In a similar test using a corn hybrid that was developed to contain
higher than normal amounts of oil (high-oil corn), the pattern was similar,
but insect survivability was greater at every level of kernel damage.
All of the larvae survived when provided with a diet of all broken corn
kernels, 81% survived on diet that contained 5% broken kernels, and
28% survived on a diet that contained only whole corn kernels. These
results indicate that it would be helpful to clean high-oil corn before
storage to reduce problems with stored grain insects. The results also
indicate that insect problems might be slightly greater in stored high-oil
corn than in corn that has normal levels of oil.
Although these tests were conducted with just one species of insect
(Indian meal moth), there is reason to believe that the results would
also apply to other types of stored-grain insects. Indian meal moths
are “secondary pests”–insects that feed primarily on
broken grain or on molds that grow on broken grain. Stored grain surveys
indicate that the most common stored-grain insects in the upper Midwest
are “secondary pests.” (The most commonly found insects in
upper-Midwest storage bins include the rusty grain beetle, red flour
beetle, saw-toothed grain beetle, Indian meal moth, larger black flour
beetle, foreign grain beetle, and hairy fungus beetle.) This means that
cleaning grain to remove broken kernels should make life difficult for
our most common stored-grain insects.
Of course, there are other good reasons for cleaning corn besides reducing
the risk of problems with some types of stored-grain insects:
- Research has shown that mold (fungi) grows much faster on broken
corn kernels than on whole kernels, so cleaning grain to remove broken
kernels also reduces the chance of mold problems.
- Broken kernels plug the air spaces between whole kernels, which
increases the airflow resistance of the corn. High airflow resistance
means that it takes more fan power to provide the airflow needed to
dry or aerate grain. Or, for a given fan, higher airflow resistance
means that the fan provides less airflow, which means that it takes
longer to dry or to aerate the grain.
- Broken kernels tend to concentrate under the fill spout when a storage
bin is filled. These concentrated areas of broken kernels, which are
already more likely to support insect life and mold growth, are also
difficult to dry or aerate because they have high airflow resistance
and air moves around rather than through them.
- High levels of broken kernels can lead to price discounts when grain
is sold. You might be able to avoid price discounts by cleaning the
corn to remove some of the broken kernels.
For more information about managing stored grain, see the Biosystems
and Agricultural Engineering postharvest website at:
http://www.bae.umn.edu/extens/postharvest/index.html,
or contact Bill Wilcke, wilck001@umn.edu
or Colleen Cannon, cacannon@umn.edu.
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