Soil insect research made easier

It has been said that, due to its tedious nature, soil insect work has turned more than one good entomologist into an administrator. But that could change thanks to work being done by University of Georgia researchers.

“We've all been frustrated working with soil insect problems, and we decided to do something about it,” says Steve L. Brown, University of Georgia Extension entomologist. “With funding from the National Peanut Board, we initiated a project to construct a prototype for a mobile soil insect screening machine designed to facilitate labor-intensive soil insect research.”

In the past, if a grower or researcher wanted to know what type of soil insect was in the field, feeding on peanut pods, he had to pull a rather large soil sample, says Brown.

“You had to bag it up, transport it to a shade tree somewhere, and use a screen as a sieve. It is a very labor-intensive, tedious way to conduct research. We decided we wanted to automate this process as much as possible so we could take our data in the field without moving dirt from one place to another.”

Brown and other researchers set about designing and building a machine that would ease the process of collecting soil insect data. “We pull this machine into the field with a tractor. It's a glorified sieving machine with a series of four screens. A bucket on the side of the machine is lowered, soil samples are placed into it, and the soil is lifted up and dumped into the trays. Soil is washed through the screens, and we retrieve the insects from the screen. The screens can be tilted upwards and washed and flushed for the next sample,” says Brown.

Each sample, says Brown takes about 15 to 20 minutes. By comparison, the traditional method takes about one hour per sample. The machine, he adds, has tested well for efficiency. In fact, it can be 100 percent effective, depending on how much time is spent with each sample.

“If you start looking at the sandy loam soils like we have in Tifton, it's amazing how many rocks you'll find. And when you start looking at a strip-till situation, where you have a large amount of organic matter, you get quite a collection in that top screen,” says Brown.

The screening machine, says the entomologist, saves time and money for researchers, but it also is proving valuable for growers. “We're trying to use this machine to gather data that we otherwise couldn't obtain because we don't have the money or the time,” he says.

In particular, researchers are taking a closer look at soil insect pests such as wireworms, says Brown. “Wireworms are very common in Georgia peanut fields, and we've known for a long time that there are several different species. They all have different lifecycles. Some have a two-year lifecycle, and others may have three lifecycles in one year. There are very different species that require very different management techniques.

“It's difficult to study wireworms because it's such a problem removing them from the soil. This machine is making it much easier. Within just a few hours, we can process samples and determine how many wireworms are present and which species are present.”

In tests conducted in fields in Alabama and Georgia, one wireworm species was found to be dominant in one location while another species was more dominant in the other location, even though the fields were relatively close together, says Brown.

“One month later, in the same field, we found a different species. This is a very dynamic and changing insect, and this machine gives us an opportunity to see a picture in time of what is happening in the field.”

The machine also is being used to look at the effect of tillage on soil insects, notes Brown. “We know that some soil insects prefer conventional-tillage while others prefer conservation-tillage. We don't have a lot of information in this area, but we're starting to get some answers.”

The soil insect screening machine was used in several locations this past year, he says, to determine if certain insects are more likely to be found in conventional or conservation-tillage situations. Researchers looked for wireworms, Southern corn rootworms, burrower bugs and white grubs in three locations, he says. They also looked for pod damage.

“The trend is becoming clear — we're seeing more damage and more insect populations in the strip-till versus the conventional-tillage peanuts.”

The burrower bug has been around for a long time, says Brown, but it is beginning to attract more attention due to the increase in strip-tillage peanut production.

“Whenever you take tillage out of your production system, you start to see changes, and one of those changes is an increase in burrower bugs. This insect doesn't like tillage, and if you put a harrow in your field, you won't see a burrower bug for a while. But if you take out tillage, they'll start to build up, and they can build up in incredible numbers.

“They're like miniature stinkbugs. They have the same type of mouthparts as stinkbugs, and they feed through the pod, through the seed coat, and into the kernel where they suck the juice out of the developing peanut. The damage is visible only in extreme cases. A peanut can appear to be perfectly normal because the blemishes are beneath the seed coat.”

In the past two years, several Georgia peanuts fields have graded Seg. 2 because of burrower bug damage, says Brown. Research from South Carolina has shown that peanuts with burrower bug damage are more likely to have aflatoxin, increasing the chances of those peanuts grading Seg. 3, he adds.

“Burrower bugs also are worse in dry weather. If you have dry weather, and you're in a reduced-tillage situation, you could have problems with burrower bugs.”

Auburn University research, he says, is looking at insect populations in different cover crop situations, including wheat, rye, oats, rye grass and fallow.

“There's no difference until you get down to fallow. Then, you see a significant increase in burrower bugs where there was no tillage in the off-season.”

Lorsban insecticide does a good job on burrower bugs, says Brown. “But we need to know when it'll pay us to use a soil insecticide and when it won't pay, and this screening machine is helping us to come up with some specific recommendations.”

e-mail: [email protected]

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