Source: AMVAC news release

Treating corn rootworm hybrids with AMVAC soil insecticides boosted yields an average of 9.1 bushels/acre in university trials across the Corn Belt in 2007 and 2008.

The 64 yield comparisons, which were conducted by university researchers at 11 universities and colleges, compared YieldGard and Herculex trait corn alone and in combination with various soil insecticides. Insecticides included Counter 15G, Fortress 5G, Aztec 4.67G and Force 3G applied with the SmartBox closed handling and application system.

Researchers participating in the studies were from the University of Illinois, Iowa State University, Joliet (IL) Junior College, Purdue University, Ohio State University, the University of Kentucky, the University of Missouri, the University of Nebraska, Pennsylvania State University, Virginia Tech and the University of Wisconsin.

"Based on these results, we are confident most farmers would realize a positive return on investment from using this practice," said Paul Vaculin, marketing manager for granular insecticides and closed delivery systems at AMVAC Chemical Corp., which sponsored the trials.

Notably, 74 percent of the trials showed a yield increase. Yield increases of greater than 10 bushels/acre were observed in 40 percent of trials and greater than 15 bushels/acres in 27 percent of the trials.

"This practice is a great fit for growers who are seeking maximum economic yields," said Vaculin. "Corn soil insecticides provide an added measure of control of secondary pests over that provided by the seed-treated insecticides and also provide complementary control of corn rootworms in heavy rootworm pressure areas."

AMVAC undertook sponsorship of the trials at the request of growers, who had noticed a yield benefit from applying insecticides to corn with in-plant corn rootworm protection. The growers conducted informal trials using the SmartBox system, which allows insecticides to be turned on and off from the tractor cab. "We wanted to test this idea to see if it was valid," said Vaculin.

The university trials were not designed to determine why the soil insecticides improved yields. However, a combination of factors could be responsible, said Rich Porter, AMVAC's technical manager for granular insecticides.

"Besides controlling corn rootworm larvae, all of the soil insecticides in the trials control secondary insect pests, such as wireworms and grubs," he said. "Since Counter is also a nematicide, suppression of corn nematodes is a factor in trials where Counter was applied. Enhancing control of one or more of these pests could be at play in individual trials."

In addition to improving yield, using soil insecticides with traits also provides added root protection so that corn is standing better at harvest, Porter said.

"In a small number of university trials, the rootworm trait was challenged," he added. "In those trials, the addition of the granular insecticide substantially reduced root feeding and held a higher percentage of roots below an economic threshold."

Another benefit of using a soil insecticide in conjunction with rootworm hybrids is that it provides a second mode of action for resistance management, he said. "If a soil insecticide is present, it has the opportunity to control rootworm larvae before feeding begins on the Bt toxin in corn roots. This has the potential of reducing development of resistant rootworm biotypes."

In most of the 2007 and 2008 trials, soil insecticides were applied at lower labeled rates - typically at three-quarters of the full rate recommended to control rootworms. For 2009, AMVAC is recommending application at the low-end label rate of Counter or Fortress in conjunction with rootworm hybrids. At these rates, and with a 2009 promotion called the Fortress SmartBucks rebate, these insecticides will typically cost $12-$16/acre.

Growers interested in trying corn rootworm insecticides with traits should consider using the practice in three situations, Porter said. These include: 1) fields expected to have heavy corn rootworm pressure; 2) fields where they want extra protection against secondary insect pests; or 3) fields with a history of corn nematodes. In that case, the product of choice would be Counter, since it is the only registered granular soil insecticide in corn that is labeled for nematode control.

To encourage growers to evaluate the value of applying corn soil insecticides with trait corn in 2009, AMVAC is offering a program called the Bushel Booster Yield Challenge. Under the program, growers will be paid $12/acre if yields from trait/soil insecticide treatments with Counter 15G or Fortress 5G aren't at least 3 bushels/acre higher than a trait-only check strip.