Double Duty

U.S. soybean growers have always searched for tools to help them achieve greater yields. As early as the 1800s, growers understood that the nitrogen level in soil could play a leading role in producing more bushels per acre.

As a result, American growers began importing soil containing Rhizobium, a beneficial symbiotic bacteria that naturally supplies soybean plants with nitrogen. Little did they know that those shipments from Asia, where the bacteria was particularly plentiful, contained a pathogen that would become the No. 1 source of yield loss in soybeans1—the soybean cyst nematode (SCN).

A Complex Relationship

The first report of this microscopic, parasitic pathogen in U.S. soil occurred more than six decades ago near Wilmington, North Carolina. Today, the pest can be found in every soybean-producing state in the country.

Jeff Simmons, a research and development scientist at Syngenta in Vero Beach, Florida, focuses his research on nematodes. The effects SCN has on soybean yields, he says, are threefold. “The roots are damaged when nematodes enter the plant to feed. Their feeding takes away vital water and nutrients from the plant. Punctures made by nematode feeding also allow diseases to enter the roots.”

Roots provide soybeans with a strong foundation and, if compromised, can leave plants vulnerable to diseases. It is through puncture wounds that SCN’s partner in crime, sudden death syndrome (SDS), is able to wreak havoc on yields. SDS is one of the five most damaging soybean pathogenic pests2 and is almost always worse in fields with SCN.

Unlike SCN, SDS is typically only an issue every four to six years because it is highly environmentally dependent—cooler, moister weather at planting followed by cooler, moister weather during seed. But when it strikes, it can significantly impact yield. The causal agent of SDS, Fusarium virguliforme, also has the ability to overwinter.

Unfortunately, there are no in-season management options for SDS, and symptoms do not appear until mid- to late-August, well after infection first occurs.

“SCN normally leads to SDS being much worse,” says Dale Ireland, Ph.D., Seedcare technical product lead at Syngenta. “Any time you have a parasite, such as SCN, it reduces your plant’s ability to resist other problems, not only because of its direct impact, but also because of the significant plant stress caused by the parasitic infection. While there are exceptions, more than 95 percent of the time when SDS is yield-limiting, SCN is also involved.”

Best Strategic Options

Due to the nature of the relationship between SCN and SDS, experts recommend that growers manage them together, which requires a combination of strategies. Most growers are familiar with rotating with non-host crops and planting resistant varieties as a way to reduce the odds of seeing SCN damage in their fields. But applying an effective nematicide seed treatment is a newer strategy that is rapidly gaining momentum across the university and Extension research community, as well as throughout the seed and crop protection industry.

In 2014, the first commercial use of Clariva^® Complete Beans seed treatment, a combination of separately registered products, marked a milestone in SCN management. Clariva Complete Beans includes a lethal nematicide that provides season-long protection from SCN and also contains market-leading CruiserMaxx^® Beans with Vibrance^® seed treatment, also a combination of separately registered products. Over the last two years, Syngenta on-farm testing at 50 locations shows that because it manages SCN so effectively, Clariva Complete Beans increases yields by an average of 2.6 bushels per acre or 4.6 percent over an insecticide/fungicide seed treatment.

“Using SCN-resistant varieties, crop rotation and Clariva Complete Beans combines all of the tools in your toolbox to manage SCN,” says Ireland. (See “Managing Resistance”.)

SDS Management: A One-Two Punch

To prevent SDS, one of the most important factors is the use of resistant varieties. The NK^® Soybean portfolio offers industry-leading3 SDS-resistant varieties to help growers manage the disease. For Syngenta Seed Advisor^™ and grower Jake Hoalt of Flat Rock, Illinois, this strategy is at the top of his list.

“The biggest thing you can do to manage SDS is select the right variety,” he says. “Adding Clariva Complete Beans makes it the full package deal. You have one of the best soybeans on the market, healthwise, and the nematicide protects the soybean from SCN, which goes hand-in-hand with keeping out SDS.”

An additional option that works in combination with choosing the right variety is adding Mertect^® 340-F fungicide to the seed treatment, which can be used on soybeans as of this year. According to Ireland, Mertect 340-F is a reliable solution to manage SDS, because it provides early-season protection from Fusarium virguliforme and works in conjunction with Clariva Complete Beans to minimize the early infection and damage that SDS can cause.

NK brand retailer and grower Marc Mummelthei of Waverly, Iowa, is relying on the co-application of Clariva Complete Beans with Mertect 340-F to protect his customers’ soybeans from the ravages of SCN and

"Any time you have a parasite, it reduces your plant’s ability to resist other problems. ... While there are exceptions, 95 percent of the time when there is SDS, SCN is also involved."

SDS. In 2015, he recommended that growers in his area treat all of their soybeans with this combination to help maximize their yields.

“If you want to get the highest yield possible, you have to put everything you can into your crop—whether it be fertilizer, fungicides, seed treatments—and give it every opportunity to yield best,” Mummelthei says. “2015 has been a great year for us to watch Clariva Complete Beans with Mertect 340-F. The weather set us up for a potential SDS nightmare. It’s been exciting to see how well they performed.”

The Value of Prevention

Decreased commodity prices in 2015 have many growers considering cutting back on inputs, such as seed treatments, to reduce costs in 2016. While paying less upfront might seem like an avenue to save money, the impact of leaving plants vulnerable to prevalent pathogens like SCN and SDS is not worth the risk.

“We saw really heavy SDS in 2014,” says Hoalt. “Growers experienced how yield-dropping the disease can be. Whenever you’re talking about seed treatment, which only adds a couple of dollars to your expenses, I think it’s pretty easy for growers to pull the trigger on the extra cost.”

SCN can often go undetected. Identifying population thresholds can help growers choose an effective course of action to manage the nematode. To determine populations, Simmons recommends sampling at the end of the season when populations are the highest.

Brad Weger, a grower from Robinson, Illinois, is familiar with the importance of soil sampling. “We’ve never had much of an issue with SCN, but last year we had a few hot spots show up that we’d never seen before,” he says. “That got us thinking: How much damage do we actually have that we don’t notice?”

Realizing the potential of SCN-related damage, Weger, who plants 100 percent NK Soybeans, treated every acre with Clariva Complete Beans in 2015. “We are big on preventive maintenance. We think that if something is going to work, we are not scared to spend a little extra money.”

The quest for new tools to maximize yields and return on investment is one that will never end for soybean growers—or Syngenta. “From disease-resistant varieties to new seed treatments, we are always on the hunt for game-changing solutions to growers’ most challenging problems,” says Ireland. “It’s exciting when our technologies can positively impact yields and improve our customers’ bottom line.”