ANR-1126, New Aug 1998. Kathy Flanders, Extension Entomologist, Entomology, Auburn University, Steve Brown, Extension Entomologist, University of Georgia, Richard A. Shelby, USDA-ARS, and Paul L. Mask, Extension Agronomist, Agronomy and Soils, Auburn University

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IPM Tactics for On-Farm Stored Grain

All the expense and effort of making a crop can be wasted if not enough attention is paid to storage. The key to storing grain successfully is to make storage conditions unfavorable for the survival of stored-grain insects and molds. The following steps are designed to reduce the initial number of insects in the bin, slow the development of any remaining insects, and apply corrective measures to reduce insect populations if necessary. Following these steps will also greatly reduce stored-grain molds and associated mycotoxins. More information on molds and mycotoxins is found in the last section of this publication.

Clean the storage bin thoroughly to eliminate starter colonies of insects (Figure 1). Every few years, remove the bin floor to clean underneath it, or fumigate to kill insects hiding beneath the floor. Don't forget the auger pit.

Seal any gaps or holes in the sides of the bin, using caulk or polyurethane foam (Figure 2). Have someone temporarily close the grain hatch so you can see if there is any light shining in through holes.

Apply an EPA-approved insecticide on the floors and sides of bins to eliminate insects hiding in cracks and crevices and to create a first line of defense against any insects that do find their way into the bin (Figure 3).

Figure 3. Treat the empty bin with an approved insecticide.

Clean the grain to remove excess fine particles and other foreign debris. Fine particles reduce aeration efficiency as well as the effectiveness of grain protectants and grain fumigants.

Dry the grain to the recommended moisture content (Table 1). Insects and molds require moisture to survive.

Table 1. Recommended Maximum Moisture Content for Grain in Aerated* Storage Conditions

	Planned storage time before marketing
Crop	6 months	6 to 12 months	more than 1 year
Corn and sorghum	14 percent	13 percent	12 percent
Soybeans	13 percent	12 percent	11 percent
Small grains	12 percent	11 percent	10 percent
Edible beans	14 percent	12 percent	10 percent
*Decrease each moisture content percentage by 2 percent if storing grain without aeration.

Apply an approved protectant insecticide to the grain as it is loaded into the bin. The insecticide can be applied in the auger pit, or it can be introduced into the elevator stream after the grain leaves the drier.

Level the grain surface. Moisture accumulates in a grain peak (Figure 4). Microbial activity in the wet area will heat the grain and attract secondary insects. The peak also reduces aeration efficiency, as does overfilling--do not fill the bin all the way to the top. Leave at least a few feet of air space.

After loading, seal any unnecessary openings in the storage bin. This is a good place for insects to enter.

Aerate the grain to cool it to at least ambient temperature (Figure 5). The hotter it is, the faster insects grow. Stored-grain insects barely stay alive when temperatures are below 60 degrees F. As nights get cooler in late summer and fall, cool the grain at 10-degree intervals until the temperature is 60 degrees F.

Figure 4. Avoid grain peaks because they tend to become moist.	Figure 5. Use aeration to make the storage temperature unfavorable for insect growth.

A 0.1 cfm (cubic feet per minute per bushel) aeration fan can be used to reduce the grain temperature. Using a fan, it will take approximately 120 hours of cooling to reduce the grain temperature by 10 degrees F, such as from 90 degrees to 80 degrees F. Automated aeration controllers make this job simple by turning the fan on and off to admit air only when the outside air temperature is between the desired temperatures. Bins can be easily and inexpensively equipped with internal temperature probes that display actual grain temperature, which also makes aeration easier.

Initiate a systematic and thorough insect-monitoring system. Check the grain every 20 days from spring to fall and every 30 days in winter (Figure 6) for the presence of insects (Figures 7 through 9). Five trier samples (Figure 10) or probe traps (Figure 11) should be sufficient on each sampling date. Pheromone traps in the head space may also be useful (Figure 12).

Figure 6. Five samples, one from the center and four from about 2 feet from the rim, will be sufficient to monitor insects in most on-farm bins.

Figure 7. The maize weevil and its relatives develop inside whole grains.		Figure 8. Indian meal moths feed externally on intact and broken grains.
Figure 9. Red flour beetles and other insects feed on broken kernels and fine particles.		Figure 10. Use a grain trier to sample for the presence of insects.
Figure 11. Probe traps can be inserted into the top layer of grain for 1 to 5 days to detect insects.		Figure 12. Pheromone traps are available for Indian meal moth and other insects.

If you begin to find insects, fumigate as necessary to keep insect populations below levels for your targeted marketing grain grade (Tables 2 through 4). Read the fumigant label carefully, and follow the instructions provided.

Table 2. Federal Grain Inspection Service Grade Requirements for Wheat

		Maximum allowable level
Grade	Minimum test weight (lb/bushel)	Heat-damaged kernels	Total damaged kernels	Total defects
U.S. No. 1	60	0.2 percent	2 percent	3 percent
U.S. No. 2	58	0.2 percent	5 percent	5 percent
U.S. No. 3	56	0. 5 percent	7 percent	8 percent
U.S. No. 4	54	1.0 percent	10 percent	12 percent
U.S. No. 5	51	3.0 percent	15 percent	20 percent
Sample grade - Does not meet the above grades or is unwholesome and/or low quality or has more than 32 insect-damaged kernels per 100g (~0.8%) Infested classification - Any of the above grades is classified as infested if more than two stored-grain pests are found in a 1000g sample.

Table 3. Federal Grain Inspection Service Grade Requirements for Corn

		Maximum allowable level
Grade	Test weight (lb/bushel)	Heat-damaged kernels	Total damaged kernels	Broken corn, foreign material
U.S. No. 1	56	0.1 percent	3 percent	2 percent
U.S. No. 2	54	0.2 percent	5 percent	3 percent
U.S. No. 3	52	0.5 percent	7 percent	4 percent
U.S. No. 4	49	1.0 percent	10 percent	5 percent
U.S. No. 5	46	3.0 percent	15 percent	7 percent
Sample grade - Does not meet the above grades or is unwholesome and/or low quality Infested classification - Any of the above grades is classified as infested if more than two internal grain-feeding insects (weevils or lesser grain borer) are present in a 1000g (2.2 lb) sample; or one weevil and five other stored-grain pests are found, or 10 other stored-grain pests are found.

Table 4. Federal Grain Inspection Service Grade Requirements for Soybean

		Maximum allowable level
Grade	Minimum test weight (lb/bushel)	Heat-damaged kernels	Total damaged kernels	Foreign material	Splits	Soybean of other colors
U.S. No. 1	56	0.2 percent	2 percent	1 percent	10 percent	1 percent
U.S. No. 2	54	0.5 percent	3 percent	2 percent	20 percent	2 percent
U.S. No. 3	52	1.0 percent	5 percent	3 percent	30 percent	5 percent
U.S. No. 4	49	3.0 percent	8 percent	5 percent	40 percent	10 percent
Sample grade - Does not meet the above grades or is unwholesome and/or low quality Infested classification - Any of the above grades is classified as infested if more than two internal grain-feeding insects (weevils or lesser grain borer) are present in a 1000g (2.2 lb) sample; or one weevil and five other stored-grain pests are found, or 10 other stored-grain pests are found.

If there are too many leaks in the bin, the fumigant may never reach a lethal level (Figure 13). Seal all unnecessary openings before loading the bin, and seal the aeration fan, top vents, eaves, and anywhere else you can see light coming through the bin.

Figure 13> Poorly sealed bins are the number-one cause fo fumigation failures.

Many fumigation attempts end in failure. Be sure to leave the fumigant in the bin long enough to be effective. Read the fumigant label to determine how long it will take the fumigant to reach a lethal level. It may take a day or two to reach the desired concentration; therefore, leave the bin sealed for the recommended length of time.

To increase fumigant efficiency, place two-thirds of the fumigant pellets in the top 6 inches of grain, and place the other third in a metal or cardboard tray in the aeration duct. Do not allow the fumigant to come in contact with water that may be in the aeration duct--this creates an explosive situation. In large bins, it may be necessary to probe some fumigant as deep as possible into the grain mass.

If the bin is only partially filled, probe fumigant pellets into the grain, and then place a tarp over the grain to keep the fumigant in the area with the grain.

The new method of closed-loop fumigation can make fumigation more efficient and safe. In this method, fumigant is circulated in a pipe outside the bin from the top to the bottom and then drawn up through the grain to the surface.

Controlling Molds and Mycotoxins in Stored Grain

Molds are fungi that can attack grains and grain products at any stage of production and can produce some of the most catastrophic losses in the crop. We have all seen mold on corn left standing in the field, perhaps on an ear opened by birds. The kernels are odd colors and are "fuzzy" in appearance, like the mold on stale bread. These more obvious signs of fungi on grain are hard to miss, and common sense tells us not to eat this spoiled grain or feed it to livestock. In fact, some of the most deadly toxins are produced by fungi growing on grains, so our intuition is quite justified in this case. Fungi can also produce toxins (mycotoxins) even if the fungus is not readily apparent or visible to the naked eye, and a small amount of the fungus can contaminate an entire lot of grain, making it unsuitable for food or feed. Fungi can also grow on the grain if harvest or storage have been mishandled. With proper care, this contamination can be prevented, and if it occurs, testing can tell you whether or not the grain is safe for feeding.

There are many different kinds of fungi that can grow on grains. Some are worse than others in terms of toxins produced. In Alabama and Georgia, almost any grain can be affected by mycotoxins. Any stored grain (as well as soybeans, cottonseed, and peanuts) can be contaminated by the fungus Aspergillus if conditions are right, and the result is the production of aflatoxin, one of the most serious toxins in agricultural commodities. Only 20 parts per billion of this toxin will make the grain unusable for feed. This toxin is also dangerous if fed to dairy animals because a form of the toxin can be transferred to milk. Other possible problem fungi are Fusarium in corn and most small grains and Penicillium in any grain. These toxins produce many different types of detrimental effects in humans and animals, so the diagnosis of mycotoxin poisoning is often difficult based on symptoms. It is more easily diagnosed from suspect grain samples.

Fungi usually come from spores, which act like "seeds" of the fungus. Spores are microscopic, dustlike particles that are almost everywhere in the environment. Because they are so widespread, it is impossible to prevent most fungi from inoculating the grain at some point in the production cycle, so the best strategy for preventing contamination is to avoid conditions that will allow these spores to germinate and grow.

Preventing fungal contamination starts in the field with practices that lead to overall plant health, the cornerstone of IPM. Vigorous, healthy plants are less susceptible to attack by fungi, and this includes not only those fungi that cause grain-storage toxins but also those that cause plant disease (pathogens). Similarly, insects can increase storage fungi in two ways: by weakening the plant, making it generally more susceptible to disease, and by serving as vectors, or carriers, of the fungi. In almost every case, the insect feeding site is a point of inoculation for these toxigenic fungi, and in the field, or in storage, these feeding sites are foci from which fungal contamination begins. Insect control in the field and in storage is an absolute must if mycotoxin contamination is to be controlled in grains.

Timely and sanitary harvest is another essential ingredient in mycotoxin control. Grain that is harvested before it is fully mature contains excessive moisture that will promote the growth of fungi in storage bins. Maturity can best be judged by checking moisture content, using a moisture meter. Remember that even grain that is mature will contain excessive moisture just after a rain. There is never enough time at harvest, but a brief waiting period to allow grain to dry before combining will pay off later by preventing fungi from potentially spoiling the larger harvest in storage. Grain left in the field after physiological maturity will also begin to grow fungi due to insects, bird damage, and rain. Plants that have lodged, allowing ears to come in contact with the soil, may serve as sources of contamination, so adjusting combines to avoid picking up lodged ears will help prevent spoilage later.

Moisture is the main reason for spoilage of grains in storage. Grain that gets wet must be dried immediately before it can be placed in storage; otherwise, the entire bin may be lost to fungi. Check bins for leaks, and stop rain from getting in. Hot pockets in the bin are a sign of leakage, and when the bin is emptied, these areas of caked grain will be obvious. Try not to mix spoiled grain with sound grain.

Contaminated grain enclosed in a grain bin is a potential health hazard in the form of spores in the air. Much of that "dust" in the air in a grain bin is fungi spores, which can cause illness if breathed and can cause an explosion if there is even a spark. Always wear a dust mask if you must enter a grain bin. This will also keep you from smoking and causing that explosion!

If you suspect contamination of grain by storage fungi, have the grain tested before feeding it to livestock. Certain laboratories can test for the presence of Aspergillus and Fusarium toxins and tell you whether or not the grain is safe to feed.

For more information, contact your county Extension agent or consult Alabama Cooperative Extension System publication IPM-330, "Stored Grain Insect Control Recommendations," and Georgia Cooperative Extension Service Bulletin 1101, "Insect Management in Grain Stored on the Farm," or The Georgia Pest Control Handbook. A video entitled "Managing Stored Grain in the Southeast" is available from the Georgia Cooperative Extension Service.

For more information, contact your county Extension office. Look in your telephone directory under your county's name to find the number.