Corn research targets maize weevil

Post-harvest corn storage research is making progress in areas such as battling the maize weevil, says University of Georgia Extension entomologist Steve L. Brown.

“We've completed three years of data on maize weevil infestation in the field,” says Brown. “Maize weevil is the key pest of stored corn in grain bins, but the weevil infests corn in the field before we've even harvested the crop.”

Maize weevil infestation is the source of many problems in stored corn, he adds. “We're putting infested corn in our bins after harvest. We conducted a three-year study to find out what affected those infestation levels in the field, and we learned that hybrids can make a difference in the level of maize weevil infestation we see in fields.

“We haven't tested every hybrid, and we can't tell yet which hybrid is the best and which is the worst, but we're making progress in that area. We do think that husk coverage is a key, and we think kernel hardness has an impact,” says Brown.

Many hybrids are bred for maize weevil conditions, he says, but not the conditions that are found in south Georgia and other parts of the Southeast.

“We need to learn which of these hybrids are most susceptible to maize weevil infestation so we can avoid them,” he says.

Planting dates also can be important in the level of maize weevil infestation, notes Brown. “Corn planting dates have an impact on when maize weevils move into a field and infest corn. But in our three-year study, we saw different results in each of the three years.

“In each of the three years, we used three or four different planting dates, and we got a statistical difference each time. This tells us that this will be a difficult component to manage,” says the entomologist.

Timely harvest is another important aspect of managing maize weevil infestations, says Brown. “If we leave corn in the field too long, we're setting ourselves up for problems. We need to be harvesting at 22 to 24-percent moisture. If we get below that range, we're creating ideal conditions for maize weevils. The longer you leave corn in the field, the worse your problems will be.

“The maize weevils are completing one cycle and emerging from the corn and laying more eggs. If you're storing corn, you need to get it out before maize weevils infest it. Maize weevils are laying their eggs as early as the three-fourths milk line, and they peak about four weeks later.”

Another area of focus for corn storage research has been on fumigation, says Brown. “We rely a great deal in the small grain industry on aluminum phosphide, and products like Fumiphos and Phostoxin. I don't know of any other industry that relies so much on one chemical.

“I wish we could get rid of it because it's dangerous. But growers in the Southeast would be in a lot of trouble with managing insects in stored grain if we didn't have this product. In the recent past, the EPA threatened to remove the product from the market. Fortunately, we were able to keep it, at least for the short-term.”

Brown expects a new label at any time for aluminum phosphide products. “With this new label, we'll have to make changes in how we use this product. One change is that private applicators will have to receive special training before using the product. In the past, you could buy the product with your private applicator permit and apply it without special training. That, however, will change, and growers will be required to receive training.”

Extension personnel and researchers have conducted training throughout Georgia in the areas of aerating, sanitizing and fumigating.

“It's very important that growers know how to properly seal grain bins,” he says. “That appears to be a big problem — growers are not taking the time to seal grain bins before fumigating. Throwing a few aluminum phosphide tablets in the bin will kill a few insects on top, but it won't get the ones down deep in the bin. With just a couple of hours of work, we could seal the grain bin and get thorough kill throughout the bin.”

Many growers believe, he says, that they have about 30 minutes after placing aluminum phosphide tablets before they need to get out of the bin. But tests have shown differently, he adds.

“We don't have near that much time. Using electronic sensors, we've found that — depending on temperature and humidity — you might have as few as five to 10 minutes before you can get into trouble.”

Other research, says Brown, has looked at the use of diatomaceous earth as a protestant for stored grain. Diatomaceous earth, he explains, has been available for some time. It consists of single-cell organisms found in old ocean bottoms, and it can be mined from the earth. It affects insects to the point to where they lose water and start to dry out, he says.

The product, he says, comes in powder form in a 15-pound box. It can be applied into a grain bin in several ways, including with an air hose. “It's a relatively inexpensive product. You can treat a 2000-bushel grain bin for $10. Our research results have been encouraging. We've tried three different application methods and all three prevented the peak of maize weevils.”

Researchers, says Brown, are pushing the implementation of a proven technique that will help growers get the maximum use from their fumigants. Closed-loop fumigation is a circulation system, he says.

“With closed-loop fumigation, you're not relying on the fumigant to find its way through the grain bin on its own. You're constantly circulating the fumigant throughout the grain bin. This technique is much more effective in big bins — 50,000 to 100,000 bushel-bins. It's relatively inexpensive to set up, with some initial costs.”

Many growers, says Brown, don't realize how much loss can occur after a corn crop is harvested and placed into a grain bin. “Long-range, we want to improve the image of Southeastern grain in the United States and world markets. At the same time, we want to make stored grain management safer for growers.”

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