Gus Lorenz was looking for an insecticide to help Arkansas farmers fight grape colaspis (lespedeza worms), a pest that feeds primarily on lespedeza and soybeans, but can also chew on rice, when he ran across a new insecticide seed treatment.

The product, eventually registered as CruiserMaxx Pak, provided good control of grape colaspis along with thrips, soybean aphids and bean leaf beetles in soybeans. But Lorenz noticed something else about the treated soybeans.

“You could see a growth difference between the plants that received the seed treatment and those that did not,” said Lorenz, an Extension entomologist with the University of Arkansas. “I thought to myself ‘that’s well and good,’ but let’s see what happens when we take it to yield.

“We harvested 10 more bushels per acre in the soybeans with the seed treatment,” he said. “That’s when I got more interested.”

Lorenz asked Syngenta Crop Protection representatives to begin working with the seed treatment, a combination of Syngenta’s thiamethoxam insecticide and its ApronMaxx RFC fungicide, on soybeans.

The entomologist also began expanding his own tests outside the initial target area — Woodruff, Poinsett, Cross, St. Francis and Lee counties in northeast Arkansas — where the lespedeza worm had been especially devastating on soybeans and rice in 2002 and 2003.

“We were surprised at Gus’ findings,” said Tony Laurens, who works with seed treatment products for Syngenta. “We weren’t planning to market CruiserMaxx Pak in the South because we were targeting it for soybean pests such as the soybean aphid in the Midwest.”

Speaking at the Mid-South Ag-Technology Field Day held at the Memphis, Tenn., Agricenter July 28, Laurens said that soybean plants from seed treated with CruiserMaxx Pak appear to be a “little taller and a little greener” than the nontreated soybeans. Syngenta representatives have been calling that a vigor effect.

“We’ve also seen yield increases ranging from 2 bushels to 9 bushels per acre across wide-ranging environments,” he noted. “This year we’re trying to define what’s happening to those plants in the field.”

Although Syngenta initially planned to market the product against soybean aphids in the Midwest, Laurens said Mid-South farmers are beginning to see a lot more soybean aphids, particularly in northeast Arkansas and west Tennessee. Thrips also seem to be a growing problem in Mid-South soybeans, according to Lorenz.

“We’ve known that the neonicotinoid insecticides seem to have an effect on the plants beyond the insect control,” says Lorenz. “But we’re not sure what it may be accomplishing in this case.”

He says the difference in the treated and untreated plants is more pronounced when the soybeans are “about knee-high. The difference appears to level out after that. And you don’t always get a 10-bushel increase. You have to put a combine in it to see.”

Although he discussed the product with farmers who stopped at the Syngenta plots at the Ag-Technology Field Day, Lorenz said he wasn’t promoting any company’s products.

“What interests me is the bottom line for soybean producers in Arkansas,” he said. “If we can increase our yields and the expense doesn’t cover up the profits, then I’m all for farmers using it.”

Now in his third year of tests with the material, Lorenz says he does think the yield increase with CruiserMaxx Pak needs to be about 4 bushels “to pencil out for farmers. At $11 an acre, 2 bushels will barely cover it; 4 bushels will cover the costs.”

And, while he is now testing the product all over Arkansas, he thinks it may have a better fit in areas with severe problems with soil-feeding insects, such as grape colaspis, wireworms and bean leaf beetles.

“We’ve had two years of positive results with CruiserMaxx Pak,” he said. “If we have good results this year, we probably will make recommendations for using it, particularly in areas where we have soil insect problems.”

But he cautions farmers to be realistic in what the treatment can accomplish. “Dryland growers won’t have any play in this. If you’re averaging 40 to 50 to 60 bushels per acres, this will probably help.”

Lorenz also has been evaluating seed treatments with Gaucho Grande, the new seed treatment material from Bayer CropScience that received a label on soybeans in 2005.

e-mail: flaws@primediabusiness.com