Know to Control

01:54AM Apr 26, 2014
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Farm Journal Field Agronomists lead two-year study to determine the best control measures for soybean cyst nematodes

Layering management and technology is a winning equation. The same is true when addressing one of the biggest pathogens—soybean cyst nematode (SCN). 

Farm Journal Field Agronomists Ken Ferrie and Missy Bauer, in partnership with Syngenta, have spent the past two years learning more about managing SCN. The microscopic roundworms don’t produce much above-ground damage; instead they feed on roots, which can cause severe yield loss.
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The Farm Journal Test Plots crew worked with Syngenta to look at how genetics and seed treatment can be paired to control soybean cyst nematode.

"It’s not like gray leaf spot in corn where farmers can see the problem so they know they need to manage it," says Bob Lawless, an agronomic services representative for Syngenta who works in northeastern Illinois. Under the worst circumstances, SCN can reduce yields by as much as 50%, or 20 bu. to 30 bu. per acre. 

"The first step to managing SCN is measuring and mapping the hot spots in your fields," Ferrie explains. "Soybean cyst nematode pressures can vary widely across a field."

Farmers should follow sampling procedures to measure pressures and inspect soybean roots for damage or the presence of female nematodes. 

Because of the pest’s spotty pressures, sometimes farmers underestimate SCN damage.

"It’s the No. 1 soybean pathogen," Bauer says. "That fact is the driving force behind our crew wanting to learn more about how we can manage this pest for maximum yields."

The known methods for controlling SCN are crop rotation (including cover crops), genetics and seed treatments. A survey done by Syngenta found that farmers estimate they lose as much as 3 bu. per acre despite using SCN-resistant varieties and rotating fields to corn. This threat leads some farmers to add a seed treatment to their soybeans.
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To better understand the tools to manage the pathogen, Ferrie and Bauer conducted field trials in central Illinois and southern Michigan.

The protocol included two varieties, one being SCN-resistant. Each variety was planted with and without the Avicta Complete Soybeans seed treatment. From year-to-year some of the varieties changed, but they always had similar maturities. 

Both years, the test plots crew pulled samples prior to planting to have an idea of the pressures in each field. Then, they evaluated root growth and condition as well as plant growth. 

In 2013, the Michigan test plots included one field in a corn–soybean rotation and one in soybeans after soybeans. The plots included the four treatments, replicated three times. 

In the soybeans-after-corn field, the cyst nematode pressure was low. Using the Michigan State University (MSU) scale, three of four management zones had a risk index of 1, and the fourth zone was zero. 

"We planted this field to twin-row soybeans and saw improvements in stand with the seed treatment even though 2013 provided ideal emergence conditions. The seed without Avicta did not have any other seed treatment," Bauer says.
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In first-year strip trials, the Farm Journal Test Plots had access to both of the soybean cyst nematode seed treatments from Syngenta. These results are from an area with medium pressure.

Yields jumped from 1 bu. to 3 bu. per acre when the Avicta seed treatment was added to the non-cyst-resistant and cyst-resistant varieties, respectively. 

In the soybeans-after-soybeans field, the crew found heavier pressure—rated at a 2 on the MSU scale. The field was planted in 15" rows. 

In the more moderate-pressure areas, the SCN-resistant variety treated with Avicta yielded 14 bu. per acre more than the SCN-susceptible variety without treatment.

"We know in order to increase yields, we have to succeed at increasing the plant stand per acre, the pods and seeds per plant and the seeds per pound," Bauer says. "Avicta was a new tool in our management toolbox. In those two years, we saw consistent responses to the Avicta product as an additional way to manage nematodes on top of rotation and genetics." 

Corn-soybean rotation. In Ferrie’s 2013 test plots, the corn-after-soybeans field was riddled with pockets of high SCN pressure. 

He saw a similar trend as Bauer; when the Avicta seed treatment was layered on top of SCN-resistant genetics, yield climbed. Ferrie recorded a 4 bu. response to the Avicta treatment in the high-pressure areas when comparing the treated and non-treated SCN-susceptible variety. 

For the SCN-resistant variety, the Avicta treatment added about 1 bu. per acre under medium pressure (which Ferrie defined as less than 1,200 eggs per 100 cc). This was similar to the yield responses he saw in 2012.
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This photo from 2013 shows the roots of the susceptible variety with and without the Avicta seed treatment, which protects roots from cyst nematodes. 

The Illinois crew also conducted limited strip trials with the recently introduced Clariva Complete Beans seed treatment. Clariva is a biological nematicide seed treatment that will be available this growing season. 

Both Clariva and Avicta seed treatments combine nematacides with CruiserMaxx and Vibrance insecticide and fungicide, respectively. However, the active ingredient in Clariva Complete Soybeans, Pasteuria nishizawae, is a natural parasite to SCN and only works on SCN. The spores of the Pasteuria nishizawae attach to the SCN and kill it while using the SCN’s body to reproduce more Pasteuria nishizawae spores. 

"We are changing our nematode seed treatment offerings," says Palle Pedersen, Seedcare Technology manager with Syngenta. "In the Midwest, we will offer Clariva Complete Soybeans because it controls the top pest they have in fields, whereas in the South there is a broader spectrum of nematodes and the Avicta Complete Soybeans product provides the needed control."
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Results from two years of plots show that even when cyst nematode pressure is low, there are benefits to improving genetics and using a seed treatment. 

The strip trials for Clariva were placed in the zones with the highest soybean cyst nematode pressures to learn more about the new product’s control capabilities. First-year numbers showed a strong response to Clariva—equal to or slightly better than the Avicta product. 

Like Bauer, Ferrie also advocates that farmer’s know their SCN pressures when selecting variety and treatment options. 

"We pull samples as well as investigate areas that show up on NDVI or thermal mapping," Ferrie says. "That goes for this plot as well as many of our production acres. Farmers need to know if they are trying to manage a problem across 10% of a field or a majority of the field."

Knowing how widespread SCN affects your fields drives your management practices. 

Beyond the seed treatments, the test plots also highlighted the value of the genetics package in the varieties. 

"Using SCN-resistant varieties has been the norm for many years because they really help manage SCN," Pedersen says. "However, many Extension nematologists now say SCN-resistant varieties are not managing SCN populations as well as they used to.
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In soybean-after-soybean fields with moderate cyst nematode pressure, yields reflect improved management through genetics and use of a seed treatment. 

"It takes a system approach that includes both SCN-resistant varieties, crop rotation and seed treatments to manage it," Pedersen adds. "Farmers who have used SCN-resistant varieties for many years and aren’t getting the same benefit out of them anymore will need to change to a new tool such as Clariva Complete Beans and Avicta Complete Beans to protect genetic yield potential."

Pedersen also recommends that farmers stay on top of the cyst nematode pressures in their fields. 

"It’s a big challenge to manage the pathogens of the future," he says. "Perhaps, it’s even more complicated than we think and will test us even more."

The Farm Journal Test Plots program and the agronomists hope to continue these partnerships to look at the available technologies and controls for their growing regions.

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