Quick Facts...
- Stored-grain Insects often cause as much loss after harvest as
crop pests cause during the growing season.
- Insects cause losses by direct feeding damage and also
deterioration and contamination of grain.
- Six steps to prevent and control of insect damage are: keep bins
clean and repaired; use residual sprays; store only clean, dry
grain; aerate the grain; protect the grain; and inspect the grain
regularly.
The profits from producing a crop should not be allowed to
waste away in storage. Stored-grain Insects often cause as much
loss after harvest as crop pests cause during the growing season.
These losses are caused in two ways:
- Direct feeding damage
results in reductions in weight, nutritional value, germination
and market value.
- Deterioration and contamination from the
presence of Insects results in downgrading of grain and market
value due to insect parts, odors, molds and heat damage. For
example, current FGIS regulations call for the downgrading of
wheat to sample grade if the insect levels in Table 1 are
exceeded.
| Table 1: FGIS infested designation standards. |
| Crop | Insects per Kg of grain to receive FGIS "infested" designation |
|---|
| Wheat, rye, triticale | More than 1 weevil, or 1 live weevil plus any other live stored grain insect, or no live weevils but 2 or more other live stored grain Insects. | | Corn, barley, oats, sorghum and soybeans | More than 1 weevil, or 1 live weevil plus any 5 or more other live stored grain Insects, or no live weevils, but 10 or more other live stored grain Insects. |
Stored-grain Insects are divided into primary pests that attack whole
kernels and secondary pests that feed on broken or cracked grain. An excellent
aid in identifying these Insects is U.S. Department of Agriculture Handbook
number 500, Stored-Grain Insects, prepared by the Agricultural
Research Service. A much more comprehensive reference is Management
of Grain, Bulk Commodities, and Bagged Products, Oklahoma State University
Extension Circular E-912.
Although storage conditions in Colorado do not favor stored
grain pest Insects, serious infestations can develop, especially
in grain held for several years. In an unpublished 1972
study, S. Pilcher found that the common primary stored-grain
pests in Colorado were the granary weevil and the lesser grain
borer, while the most common secondary pests were the sawtoothed
grain beetle and the flat grain beetle. In a more recent USDA
study, 25 percent of 159 samples of Colorado farm-stored wheat
were infested with an average of 3,645 Insects per bushel of
grain. Eighty-six percent of 14 samples of corn averaged 200
Insects per bushel of grain. One of two samples of oats averaged
96 Insects per bushel.
Winter conditions in Colorado are such that losses in the first storage
season are minimal and will continue to be if the proper precautions are
taken. A six-step prevention and control program is recommended. Registered
insecticides can be found in the current High Plains Integrated Pest
Management Guide available at www.highplainsipm.org. Read
and follow all label instructions.
Six-Step Prevention and Control Program
Step 1: Keep bins clean and repaired.
Never store new grain on old grain, mix it with old grain or
store it in a dirty bin. Old grain and debris are the most
important sources of Insects that attack new grain. Completely
remove and burn all old grain, broken kernels and other debris.
Clean anywhere spilled grain may have accumulated, including
outside the bins, behind partitions, between walls and under
floors. Fill any holes to prevent access by birds and rodents.
Check the roof, as moisture from rain and snow can encourage
insect development.
Clean harvest and grain-handling equipment before harvest.
Avoid storing grain near feed storage, animal feeders or stables. These areas may be sources of grain-infesting Insects.
Step 2: Use residual sprays.
After cleaning, treat all bin surfaces, including removable
doors, behind partitions, and under floors, with an approved
insecticide about two weeks before storing grain. The dosage will
vary with the porosity of the surface being treated. Malathion
may not be effective where Indian meal moth is a problem. Remove
Insects killed by this treatment to avoid contaminating new
grain.
Step 3: Store clean, dry grain.
Moisture of corn should be less than 15 percent, while other
grains should be at 12 percent or less. Minimize cracked kernels
and other dockage. They allow some grain pests to build up at
much lower temperatures than are required with whole grains.
Step 4: Aerate.
Proper aeration of the grain ensures uniform temperatures
and thus avoids moisture buildups that encourage mold
development. Molds directly affect grain value. They also serve
as alternate food sources for some grain pests, which increases
the insect problem.
Step 5: Protect the grain.
insecticides may be used to treat grain as it is moved into
storage. Check the label for proper dosages. These materials also
may be used to treat the surface of the grain to provide a
protective barrier against infestation. This barrier is broken
whenever the surface is disturbed, such as during inspections for
Insects. Retreatment is recommended after inspections.
If Indian meal moths or other surface-feeding moths are a
problem, then consider available treatments given in the High Plains Integrated Pest Management Guide. These are recommended for Indian
meal moths, as many populations of this pest are resistant to
other insecticide protectants.
Step 6: Inspect grain regularly.
Below 55 to 60 degrees F, inspect grain every two weeks. Above this temperature, inspect it weekly. This will detect new
infestations early and avoid extensive damage. Use a grain probe
to take samples in a systematic pattern first from the surface
(horizontally, about 2 inches deep) and then from the bottom of
the grain mass. Inspect both the center and the area near the
walls with samples no farther apart than 20 feet.
During probing, "hot spots" may be felt on the grain surface
or off odors may be detected. These are indications of insect
activity and should be checked. During the colder months, the
Insects will congregate in the center of the grain mass, so
sampling at that location will be more important. Sift the probe
contents through 10-12-mesh screen and examine it for Insects.
Table 1 provides the number of live Insects per kilogram of
grain necessary to exceed Federal Grain Inspection Service
standards and to be branded as "infested." Elevators may have
stricter standards and may also grade down based on the presence
of insect-damaged kernels.
Consider the following alternatives if an infestation is detected:
- Move the grain and retreat as in Step 4. If the move is made during cold weather,
some Insects will be killed even without treatment.
- Feed the grain to livestock.
- Fumigate.
Fumigation of Stored Grain
Three fumigants are available, each with certain advantages, disadvantages and specific uses. The future regulatory status of these is uncertain. In the past few years, several fumigant active ingredients have lost their federal registrations for stored grains.
If the product to be used is old, check the label to ensure that all ingredients are currently approved for this use. Fumigation is both complicated and risky. Often, it is best to leave it to professionals. Read, understand and follow all label precautions and instructions. The best advice is to follow Steps 1 through 6 closely to prevent the need for this costly procedure.
Common insect Pests of Stored Grain
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| Figure 1: Granary Weevil (Sitophilus granarius). Photo courtesy USDA. |
Figure 2: Lesser Grain Borer (Rhyzopertha dominica). |
Figure 3: Indian Meal Moth (Plodia interpunctella). Photo courtesy USDA. |
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| Figure 4: Tribolium species. |
Figure 5: Sawtoothed Grain Beetle (Oryzaephilus surinamensis). Photo courtesy USDA. |
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