Soybean aphids plagued many Iowa fields during the 2009 growing season, leaving farmers to find more effective management strategies for 2010. Several seed companies are encouraging farmers to consider aphid resistance when choosing soybean varieties.

In 2010, Syngenta Seeds is introducing that company's Aphid Management System, trademarked AMS, the first integrated management system for aphid control on the market. "It starts with genetics. That's the cornerstone of a good soybean program and our NK soybean genetics are a big part of our AMS system," says brand marketing manager Matt Tenhaeff.

New trait comes from traditional breeding - it's not a GMO

Syngenta is putting the Rag1 gene, a trait for aphid resistance, into its leading soybean genetics. This is a native trait, not a GMO, so there are no grain-channeling issues or GMO registrations involved.

The next piece of the system is CruiserMaxx bean seed treatment, Syngenta's combination of insecticide and fungicide, he explains. It provides early season control, holding aphid populations down and allowing beneficial insects to work.

The final part of AMS is to scout the crop and if aphid populations do show up later in the season at economic thresholds, "we have Warrior II foliar insecticide to spray on the soybeans to clean up any situations where aphids reach economic threshold levels," says Tenhaeff.

You want to get help from beneficial insects in the field

This system gives beneficial insects a chance to work, to help control aphids. CruiserMaxx seed treatment doesn't kill ladybugs and lacewings which can consume a large number of aphids, says Tenhaeff. CruiserMaxx controls aphids early on, but can only help for so long. Then the Rag1 gene takes over to provide control, and you have the beneficial insects helping. If aphid populations do rise later in the growing season, you can spray the foliar insecticide.

The Rag1 trait has been around awhile, in group 7 and group 8 maturity beans grown in the southern U.S. "Now, we've successfully bred this resistance into Midwest soybeans to bring the Aphid Management System here," he says.

Group 2 and group 3 maturity soybeans available for 2010

Will Rag1 resistance be available in varieties for Iowa maturity zones; group 2 and group 3 soybeans? "In time they will," says Tenhaeff. "For planting in 2010, we're introducing several varieties in the early to mid-group 2 range, and introductory quantities of this seed will be available. However, for the 2011 growing season, we will have a broader selection of seed products with Rag1 resistance from group 1 to group 3 soybeans."

He adds, "The main point of AMS is the integrated approach. It uses not only leading NK soybean genetics and the resistance trait, but having CruiserMaxx on the seed allows beneficial insects to play their role. And we have a closer—if needed. That is, Warrior II can be applied if aphids reach economic threshold levels in the growing season."

Different seed companies are taking different approaches to aphid control. According to Pioneer Hi-Bred International, growers who plant that firm's seed can choose bean varieties based on aphid resistance - or antibiosis - scores.  Pioneer researchers evaluate aphid antibiosis and continue to improve aphid resistance in soybean varieties.

Some seed firms scoring bean varieties for aphid resistance

They score the soybean varieties by the plant's antibiosis properties, or inherent characteristics that discourage aphids from feeding and reproducing. The company's varieties are scored as exceptional (E), above average (AA), average (A) and below average (BA) which allows growers to prioritize field scouting and insecticide application.

Scouting for aphids is a common way to detect aphid infestations, a practice that Jessie Alt, a Pioneer researcher, and her fellow scientists promote. "We are helping growers prioritize scouting by providing these antibiosis ratings," she says. "Varieties with below-average antibiosis scores need to be managed differently than those with above-average scores. It's important to keep a close check on your particular field conditions because aphids can cause damage rapidly. If left untreated, aphids can destroy 50% of the potential yield."

Soybean aphids are no longer an every-other-year problem

First appearing in the Great Lakes area of the U.S. in the year 2000, aphids quickly have become a major soybean pest in North America, spanning to almost all soybean-growing areas in the U.S. and Canada. In recent years, aphids have shown that they are no longer an every-other-year issue, but instead can be a significant yield-robbing pest during any year.

Currently, the most effective management strategies include selecting soybean varieties with native antibiosis and timely application of insecticides. "Aphids are a major issue right now, so we're addressing the problem with a special soybean team comprised of breeders, research scientists and an entomologist," says Alt. "We conduct our controlled screenings to develop stronger antibiosis scores in different soybean varieties."

Pioneer expects to unveil new products with improved soybean antibiosis scores that incorporate the best new or novel genes conferring resistance. The level of resistance acts as a type of insurance to growers by protecting their crop from this pest while reducing the number of insecticide applications, notes Alt.

Plant resistant bean varieties, then use insecticide if necessary

"Growers can manage soybean aphids by planting resistant soybeans as the first line of defense. And they can back that up with insecticide applications if needed," she says. To find resistance to multiple aphid biotypes, researchers draw from many different sources. 

"Our research includes screening multiple areas to give us a broad idea of how our soybean varieties will respond to aphids," Alt says. "We screen aphids from several different sites around the Midwest. For example, aphids in Indiana or Ohio may behave differently than those in South Dakota or Iowa. Having multiple research sites throughout North America is a significant benefit to help us determine which products work best in specific soybean-growing areas."

Antibiosis research involves trapping aphids into the sticky cages on leaves of the soybean then observing whether the insects can reproduce or colonize. The researchers perform various testing in controlled growth centers.

Aphid damage can devastate bean varieties with low tolerance

"Our research shows Pioneer's antibiosis rating system is working," Alt says, "We test soybean varieties for their aphid tolerance level in fields ranging from those treated with varied levels of insecticide to untreated fields. It's evident how devastating aphid damage can be on fields planted to soybean varieties that have a low tolerance to aphids."

Moving forward, growers likely will see continued improvements in the area of soybean aphid antibiosis as well as resistant varieties. "There's a lot of research being done with resistant lines," Alt says. "We're stacking genes to create a higher level of resistance in the future. On-farm product advancement trials in 2010 will continue to help us determine what's working best."