“With pressure aeration, you cool the bottom of the grain first,” Casada remarks. “You have to wait for that cold front to move up while the top stays warm, and it typically takes 200 hours of fan run time for that to happen. Now, you still want to cool the bottom of the grain, but the advantage of cooling the top first is that’s where the largest insect problem is. Starting at the top gives you a big advantage with insects.”
Implications for pest management
Arthur says they anticipated the top of the grain mass would cool more quickly with suction aeration, but they were surprised at how much of a temperature difference there was and how immediate the response was from the insects.
For example, in the 2004 trial they found 3,290 rusty grain beetles and 8,210 red flour beetles in pressure aeration-cooled bins vs. 662 and 722 respectively in suction aeration-treated bins.
Although the findings are strong enough to make the case for suction aeration, it was not the better method 100% of the time. Some insect species, such as the foreign grain beetle and the hairy fungus beetle, were better controlled by pressure aeration. These findings were more prominent in the second trial that began in 2006.
“The inconsistencies could be due to the rate of cooling, the extent of the infestation when the cooling process began or the fact that different species of insects have different temperature ranges for optimum growth,” says Arthur. “But all the major species that are known wheat pests consistently showed lower populations with the suction aeration. The ones that showed lower with pressure aeration were mainly fungus feeders, which are more incidental pests, and not normally considered to be a major problem.”
Larger-scale studies are needed, but Arthur and Casada are confident that using suction aeration could reduce the need for fumigant phosphine to control insects in stored wheat.
New field trial
Based on the positive results of the first two studies, a larger scale field trial is being conducted at the ARS in Manhattan, KS. Last summer, Arthur and Casada began a three-year trial, monitoring insect pests at 12 different points in two 4,000-bushel wheat bins — one using suction aeration and one using pressure aeration.
In this trial, they are gathering more temperature measurements along the grain’s surface in the headspace of the bin and at the initial surface zone in the grain mass in order to reveal more refined temperature patterns in the two bins.
Since the research will be going on over three years, Arthur and Casada are hoping to get a better handle on the year to year temperature variation factor and its impact on pest management.
Not a catch-all
The advantages of using suction aeration for stored wheat in the South Central United States are clear, but it does not mean that suction aeration is better for all commodities in all regions.
Wheat is harvested and stored over a wide geographical area in the United States, so Arthur cautions that what they’ve found in Kansas may not be true in Northern states.
“The farther north you go, the later in the summer the wheat is harvested and stored,” says Arthur. “We think the general principles would apply — the quicker you cool off the grain’s surface, the better the insect control — but testing is required to be certain.”
Casada adds that suction aeration is not ideal under certain circumstances. “If you’re loading warm grain on top of cool grain, then you can’t use suction aeration because you would pull warm air down through the grain that has already been cooled,” he says. “That scenario is common in grain elevators when they take in warm grain and need to load it in a storage bin already cooled by aeration.”
The effectiveness of suction aeration is also questionable pertaining to soybeans, corn and other fall-harvested crops. The major difference is that in much of the United States, temperatures are already cool enough by harvest time to limit insect populations.
“Wheat has different storage considerations than most fall-harvested crops,” says Casada. “It inherently has more insect problems because it’s put in bins in warm weather. It’s quite difficult to aerate wheat to the right temperature when there are only a few cool hours in the night, so being able to modify a technique that’s already in use to increase its efficacy is helpful.”