It's such a sure-fire way to increase Southern soybean yields that one enthusiastic scientist says it's like taking money to the bank.

In Midsouth research, tankmixing an insect growth regulator (IGR) with a fungicide has been shown to enhance both disease and insect protection and boost yields more than either product used alone.

The IGR is Dimilin, which controls green cloverworm, velvetbean caterpillar, armyworm and other insects. It's tankmixed with Benlate or Topsin fungicide, both of which offer protection against diseases such as frogeye leaf spot.

Melvin Newman, an extension plant pathologist at the University of Tennessee's Jackson experiment station, has tested various combinations for several years. In 1996, he looked at Dimilin alone, Topsin alone, Dimilin combined with Topsin and Dimilin combined with boron.

"The disease ratings and yields again confirmed what we already knew -- Dimilin and Topsin in combination significantly decreases the amount of frogeye leaf spot," Newman reports.

The combination has been especially effective in such areas as Weakley County, TN, where yields are normally high, he says.

Although Louisiana growers also have seen good yield responses, their main objective is to enhance control of insects rather than diseases. Miles Brashier, county agent in Pointe Coupee Parish, established several large-scale plots in conjunction with Louisiana State University.

Brashier applied the tankmix in early June for control of velvetbean caterpillars and other worms.

"Dimilin will be a good fit early on," Brashier says. "The combination with Topsin looks really strong."

The combination has generated high interest among customers of Mike Cashio of Farmers Feed Mill in Maringouin, LA. The IGR fits best as a management tool for controlling velvetbean caterpillar and green cloverworm on Group IV to Group VI beans, Cashio says. An early application can save an insect spray later in the season. And growers who treat early don't have to worry about missing a spray threshold because they can't schedule a plane.

Although he would like to see a yield advantage, it's not the determining factor. "With our conditions here, even if yields are the same, I will be satisfied," he says.

Extension personnel at Mississippi State University combined the IGR and a fungicide in several field trials. Alan Blaine, extension agronomist, says he would like to see data from several years before making a recommendation. But the data looks encouraging so far.

"In the past, we have seen a yield response from a combination of Dimilin and Benlate," Blaine says.

"It will have a fit -- we just need to find where. Without insect pressure, I doubt we will see a benefit and the hill areas probably will see a better response than the Delta. Hopefully, our test results will get us closer to making this decision," Blaine concludes.