Elevating Grain Storage Practices

Agricultural Research, April, 2000 by Linda McGraw

Word-of-mouth advertising is important to spreading good news and good practices among people. ARS entomologist David W. Hagstrum hopes that in a few years grain elevator operators will pass on information being gathered now that could save the wheat industry millions of dollars.

Stored-grain insects account for multimillion-dollar losses annually in this multibillion-dollar industry.

Each year, 2 billion bushels of wheat are produced in the United States, with most of it being stored at one time or another in an elevator. Some is stored before milling, but much of it is awaiting export to other countries. In either case, damage to stored grain by the lesser grain borer, rice weevil, red flour beetle, and rusty grain beetle costs the U.S. wheat industry about $500 million annually.

"Pest management is important for all types of grain elevators because insects move along with grain as it makes its way through the marketing system. Failure to control pests at just a few elevators can provide sources of insect infestation that can lower the quality of much larger quantities of grain as it's commingled in the marketing system," says Hagstrum.

Hagstrum is based at ARS' Grain Marketing and Production Research Center (GMPRC) in Manhattan, Kansas. Since July of 1998, he and other Kansas and Oklahoma scientists have been monitoring insect levels and current pest management practices at 13 elevators in Kansas and 15 in Oklahoma.

In the first year of this 5-year study, the scientists gathered baseline data, taking more than 20,000 grain samples from the 30 million bushels of wheat stored at these elevators.

"This effort is unique. These aren't laboratory studies; instead, they focus on day-to-day management practices of grain elevators--how these practices affect the cost and effectiveness of insect control and how, in turn, the economics of moving and storing grain are affected," says Hagstrum.

Integrated Pest Management

A collaborative effort between major grain-handling companies, Kansas State University, Oklahoma State University, and ARS, this study is the largest of its kind. Federal and state researchers are working with elevator managers through industry cooperators who own the networks of grain elevators. The purpose of the project is to evaluate procedures that might be useful in an integrated pest management (IPM) system for wheat storage.

Sampling is a key tool for determining the level of insect infestation in the stored wheat. To estimate changes in insect populations, research technicians sampled grain from elevators in Kansas and Oklahoma and from trucks that deliver it to terminals. The researchers took three 1-gallon samples from every 1,000 bushels of wheat sampled--5 to 50 times larger than the commonly used sampling rate. They found that most of the wheat trucked to the elevators is relatively free of insects.

"Insects are detected with probe traps within a month after the grain enters the elevators," says R.F. (Skip) Allen, who manages the project in Hutchinson, Kansas. In Watonga, Oklahoma, Allen's counterpart is Stan Miller.

Hagstrum and his team identified three main ways to improve integrated pest management: (1) cooling the grain earlier in the season, particularly right after it enters the bin; (2) cleaning empty bins more thoroughly; and (3) fumigating wheat only when insect infestations reach unacceptable levels. All three practices create an environment in which beneficial insect parasites can thrive and attack the stored-grain insect larvae.

"These aren't necessarily new ideas," says Hagstrum, "but now we have substantial data to show they are cost-effective." Cooling newly harvested grain right after it enters the bin, rather than waiting until fall when elevators typically use fans to aerate (cool) the grain, can reduce insect problems and the cost of pest management. The cost of early cooling is less than fumigation, currently estimated at 1.57 cents per bushel for storage in steel bins and 2.35 cents per bushel for storage in concrete bins.

Most grain elevators have thin wire cables to check the temperature of the grain inside. These cables run through the center of the bin from top to bottom. Sensors are positioned every 6 feet along the cable for measuring temperature.

"A conscientious elevator manager records the temperatures, keeping watch for any rise in temperature that might indicate the presence of insects," says Allen.

Data loggers--small recording devices attached to the aeration fans--are being used by the IPM researchers. "With these, we can show the workers how long the fans had been running--in some cases many hours after the grain had already cooled. Being able to automatically cut back on fan operating time helps save on energy costs," says Hagstrum.

These data will be welcome news for the grain-storage industry. One-third of the storage bins included in the project have aeration fans to cool the grain, but controlling devices are needed to shut the fans off when the outside air temperature is insufficient to cool the grain, according to Hagstrum.