NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665

December 10, 1998

Warm Weather Leads to Insect Attacks on Stored Grain

This year's early harvest and the warm temperatures so far this winter provide ideal conditions for a population explosion of insects in stored grain, say specialists with the North Dakota State University Extension Service.

"Because of our early harvest we saw grain going into the bin this year at 80 F or higher and because of the warm temperatures we've had and the good insulating properties of grain, it hasn't cooled down much," says extension agricultural engineer Ken Hellevang.

Those warm temperatures provide ideal conditions for insects that feed on stored grain, says extension entomologist Phil Glogoza. Insect observations by elevator personnel and an increase in the number of requests for fumigation certifications indicate problems are developing across the state.

Some grain insect pests, like lesser grain borers, red flour beetles, flat grain beetles and Indian meal moths, are common across the region and fly from storage site to storage site. Insects like grainary weevils, sawtoothed grain beetles, mealworm beetles and spider beetles pose the biggest threat when new grain is stored in bins that were previously infested and not adequately cleaned.

The specialists advise producers to take frequent samples to monitor grain conditions in their bins. "Check the surface of the grain, then use a probe to check the moisture and temperature at a variety of locations," Hellevang says."Pay attention to the look, smell and feel of the grain. Your senses can tell you a lot about the condition of the grain."

He advises producers to watch for frost or condensation on the inside of bin roofsan indication that there is excess moisture in the grain. Examine samples under good lights. Spreading samples on a light-colored cloth may make it easier to identify insects. Bring cold samples into heated areas to warm them up, making insects more active and easier to identify.

Typically, controlling the temperature with aeration is the key, Hellevang says. Once the temperature drops below 70 F, insect reproduction slows down. At 60 F it stops altogether. At 50 F, insects become dormant. Extended periods of time with temperatures below 30 F will kill most insects in grain.

"With the warm temperatures this fall, it's been difficult to bring the temperatures down," Hellevang says. "We also have a lot of grain in temporary or marginal storage because of the large crop. Many of those storage facilities don't have adequate aeration."

Bins that hold 3,000 bushels or less are less likely to develop insect problems because they cool some without aeration. Grain serves as an insulator, having an R-value of 1 per inch. Typical homes in the region are insulated to R-20.

"Grain at the center of an 18-foot bin is insulated in excess of R-100," Hellevang notes.

In grain storage without aeration, portable screw-in aeration units may help cool hot spots and head off early problems. Moving grain from one site to another may also break up hot spots, infestations and moisture concentrations but will not significantly reduce grain temperature, Hellevang says.

Fumigation, the standard method of eliminating infestations in stored grain, is not very effective once grain temperatures drop below 60 F. "At cooler temperatures, gas isn't generated as fast, insects aren't as active and you have to hold the gas in the structure longer. Those are three strikes against an effective treatment," Glogoza explains. If temperatures are too cold, remnants of the fumigant could remain in the grain. That could make the grain dangerous to handle later in the season. Elevators will not purchase grain that contains fumigants.

"The best strategy may be to get that grain as cool as you can right now to slow insect activity and address the problem when things begin to warm up in the spring," Glogoza says. But that decision must be based on information about infestations in the grain, the temperature of the grain and the ability to aerate to bring temperatures down.

And constant monitoring is a key. "If you have an infestation that goes dormant now, it'll be ready to explode when conditions are right again in the spring," he says.

Glogoza notes that state certification is required for anyone fumigating stored grain. Typically, on-farm fumigation relies on aluminum phosphide tablets. The tablets are probed into the grain. As they absorb moisture, they dissolve, giving off phosphine gas which interferes with respiration. At temperatues above 60 F, fumigation can be completed in three to five days. At cooler temperatures, the tablets dissolve slower and fumigation may require up to 10 days.

Bins need to be sealed to hold the gas in place. "Bins tend to be leaky," Glogoza notes, "so the longer fumigation takes, the more difficult it is to hold in the gas at critical concentrations."

Fumigation applicators should not work alone and should have access to a full-face gas mask with a canister approved for hydrogen phosphide. Applicators should also use gas detection equipment.

"Unless it takes a long period of time to place the tablets, it can normally be done without a gas mask," Glogoza notes. "Detection equipment will tell you when concentrations are high. Detectors will also indicate when the gas has dissipated from bins after fumigation. If you don't have detection equipment, a gas mask must be worn whenever you are inside a bin throughout the application process."

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Sources: Ken Hellevang (701) 231-7243 and Phil Glogoza (701)231-9629

Editor: Tom Jirik (701) 231-9629