To say that a crop is “in the bin” lends a bit of finality to the whole process, but it could be just the beginning when it comes to insect damage in stored grains.
As wheat harvest begins and many growers now have an eye towards corn, it’s important to do everything possible to prevent stored grains from being infested with insects, says Kathy Flanders, entomologist with the Alabama Cooperative Extension System who specializes in grain and forage pests.
There are several major factors that can influence what happens in the grain bins, especially over the course of a winter, says Flanders. Generally speaking, careful monitoring can head off potential insect problems in stored grains.
“One important factor is simply how long grain will be stored,” she says. “The longer grain is stored, the more likely you are to have problems with insects, as they develop over time in the bins.”
Another concern, she adds, is the moisture content of the grain. “The higher the percent of moisture in the grain, the greater the likelihood that insects and molds can grow. In fact, we recommend with corn that if you are going to keep it less than six months, get the moisture down to 14 percent. Between six and 12 months, you want to be at 13 percent. If you want to keep your corn longer — for example, if you have a value-added operation and you need to keep it for an extended period — you’ll want to dry it all the way down to 12 percent,” says Flanders.
Anything at more than 14 percent will be more at risk for molds and insects developing, she says.
It’s important, says Flanders, that growers get their grain bins as clean as possible to help reduce the risk of insects starting their populations. “Corn is a special case because there are certain insects that occur out in the corn field, and when you bring the shelled grain onto the farm and put it into the grain bin, they’ll develop there. The longer corn is left out after it has ripened, the greater the likelihood it will be contaminated by some of these insects. Among these insect pests is the maize weevil, which is something we’re very concerned about in corn,” she says.
This past year was a prime example of what can happen when corn is left in the field for an extended period, says Flanders. “Because of the rain we had and all of the corn that was left in the field, it was well after the time it had ripened, and the grain that was put into bins was put in at high moisture content.”
The good news, she says, is that it is fairly easy to make a grain bin hostile to the development of insects.
“You can really apply a lot of the integrated pest management tactics to make the whole environment so that it discourages the development of insects and molds,” she says.
One of the major tools for doing this is the aeration fan or blowers in the bin, says Flanders, which can be used to drop the temperature of the grain throughout the grain mass down to below 60 degrees F.
“Insects are cold-blooded, and if you can get the temperature below 60 degrees F., you won’t be seeing any reproduction from the various insects that can infest the grain. There may be some there, but they won’t be developing at below 60 degrees.”
After the grain is placed into the bins, growers can run the fans so the temperature all the way through the grain mass is below 60 degrees F. “What may not occur to people is that they need to come back and check that grain again midway through the winter to make sure about the temperature. Grain has very good insulating qualities, so once the grain gets below 60 degrees, it tends to stay there. But here in the Southeast, with the warm periods we have during the winter, it is possible for some of the grain to heat up, maybe around the edges as opposed to the entire mass.”
If the grain does start to heat up again, it’s important to begin running the aeration fans to get it back down below 60 degrees. The more powerful the fan, the faster it is to run a cooling front through the grain, she says.
“For most of our farm bins, 24 to 36 hours of cold air will cool down the bin. Generally, if farmers don’t have a grain thermometer available, then they could just make sure they had 24 to 48 hours of cold air blowing through their bins. Hopefully, that will lower the temperature.”
The only good way to find out what is happening in the bin is to carefully climb up to the top with appropriate safety equipment.
“They make special thermometers that are on long probes. Farmers also can buy thermo-couple wires and put them in the bins as the grain is being loaded, and attach the leads to the thermo-couple reader and figure out what the temperature is farther down in the grain mass. Instead of having a thermometer at the end of a long probe, they will have cables down in four or five places to determine the temperature. If all else fails, they make temperature guns that will send a beam into the grain and give you some idea of what’s happening on the outer edges of the grain.”
If a grower doesn’t have a means of monitoring the temperature, it’s definitely better to be safe than sorry, says Flanders, because you are at a higher risk with higher moisture corn and corn that has been left in the field.
How do producers know if they have insects in their grain bins? “If you open the cover and see insects crawling around, you’re really in trouble. But there are various ways to tell if you have bugs in your grain.”
She recommends that farmers use a metal grain probe or specially designed pitfall traps.
“A good rule of thumb is to put in five traps per bin every two weeks in summer and every month in winter. Place the traps and then come back in a few days to check.”
She says these traps will detect insect activity before critical levels are reached. If farmers use a grain probe, they will have to use some type of sieve or colander to sift out the insects.
With corn, the worst possible insect in stored grain is the maize weevil, she says. “They have a long snout, and they lay their eggs inside the kernel, with the baby eating out through the kernel. They’re the most destructive.”
It’s difficult to deal with insects that already have developed all the way through the bin, says Flanders. “Many times, there aren’t a lot of choices other than to fumigate the bins or move the grain from one bin to the other, applying the insecticide after the grain is moved. It’s easier to do the preventive steps than to try and take care of the problem once it develops. Corn insects in stored grain can be devastating — you can store the grain in the fall and come back in the spring and have nothing but ‘green dust.’”
When the weather is warm enough, she says, it takes only 30 days for an insect generation to develop. Several generations can build over time and cause extensive damage.
“It’s even worse when you’re trying to sell the grain in the market because there are federal standards that must be met. If you have too many insects, you can suddenly get docked or discounted a certain amount per bushel.”
Growers also should resist the temptation to over-fill the grain bin, says Flanders. “Don’t try and fill the bins up to the tops of the roofs. That’s counter-productive to the way moisture moves, and if there’s too much in there, you can’t get around and see what’s going on. Keep the surface leveled off and no higher than the top part of the straight sides of the bin.”
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