AMES, Iowa — While Iowa didn’t experience a widespread outbreak in 2011, state agriculture officials are predicting soybean aphids will remain a looming threat in the Hawkeye State this year, as well as in portions of Illinois, Indiana and Ohio. 

“Soybean aphid is still our primary soybean pest and growers should be vigilant about scouting in 2012,” said Erin Hodgson, Iowa State University assistant professor of entomology and extension entomologist.

A nationally recognized expert on the insidious plant insect, Hodgson said some growers in the northern portion of Iowa last year had soybean aphid-infested fields exceeding an economic threshold that required a foliar insecticide to protect yield.

“Looking for aphids after bloom is especially important because long-distance migration can bring aphids from other places and cause late-season infestations,” she added.

David Wright, director of contract research and strategic initiatives at the Iowa Soybean Assoc., said soybean aphids still remain a threat to farmers every year.

“Although predicting aphid presence and severity is unpredictable, history shows us that aphid populations will reach threshold levels somewhere,” he said. “There is no way to know how severe aphids will be in 2012.

“However, since the level of aphid predictors appeared low (last fall), aphid populations may be able to surge (this) spring. There are other things, like a fungus that can keep aphid populations low.”

Hodgson is working on developing a sampling plan and economic threshold for aphids in corn. While some cornfields in northern Iowa had serious outbreaks of aphids over the last five years, she said “unfortunately, we don’t have any research-based treatment recommendations to protect yield.”

But she added that “some of the most exciting research for soybean aphid is focused on development of host plant resistance,” a new strategy found in naturally occurring germplasm, and that expresses antibiosis.

“Soybean aphids feeding on resistance plants don’t live as long or produce as many offspring as aphids feeding on a susceptible plant,” she said. “The overall growth potential of soybean aphids over the summer is slowed down. (But) host resistant plants will not be aphid-free, so growers should continue to scout.”

According to Purdue University extension entomologist Christian Krupke, vigilance in scouting their fields paid off for southern Indiana farmers last year, where the threshold was low.

“I think everyone was ready for them,” he said. “One of the reasons we had the outbreaks in the past is because we didn’t have the awareness of aphids that we have now.”

Mike Gray, University of Illinois entomologist, said soybean aphids have already overwintered in central Illinois, with early indications for higher levels this year.

Yet, after outbreak years in which Ohio typically sees aphids appearing in two-year cycles, Andy Michel, Ohio State University extension entomologist, said the Buckeye State doesn’t typically see a large migration to buckthorn or eggs on buckthorn.

“This is atypical of what we see after high aphid population years,” he said. “This could indicate that we may see significant aphid populations in an even-numbered year, in 2012, which would be the first time that happened in the 10 years we have been studying them.”

That’s why farmers should look through their fields throughout the season to see if aphids reach an economic threshold needed for spraying, said Paula Davis, senior manager, insect disease control traits, at Pioneer Hi-Bred International, Inc. in St. Louis, Mo.

“That is generally 250 aphids per plant over an average of 20 to 30 plants, if populations are increasing,” she said. “If this threshold is reached, it’s recommended to treat within seven days to prevent populations from reaching an economic injury level.”

Wright said his first recommendation in aphid management would be to “make a plan for being sure each soybean field is scouted for aphids and the presence of manageable soybean diseases such as frogeye leaf spot.

“If you can’t do it yourself, hire a good crop advisor,” he said. “A good crop advisor, or scout, can make the farmers money by providing them with field-based observations with which they can make decisions to treat, or not treat, a field.

“Correct timing of insecticide application is critical. Treating too late will result in lost yield. Treating too early may knock down an early flush of aphids, but may enable the population to rebound, resulting in the need for a second insecticide application.”

Still, Hodgson said, growers should try to incorporate host plant resistance into their seed selection and evaluate the performance, compared to susceptible soybeans.

“Infestations can be patchy, especially early in the season,” she said. “Scouting on a regular basis will provide a record of population growth so that timely insecticides can be made to protect yield. Aphids can develop genetic resistance to insecticides, so consider chemical rotation if more than one application is required.”

Pioneer is currently working on a soybean aphid-resistant trait in its research pipeline and plans to offer it to growers in the future, Davis said.