Farm Progress

SDS and SCN: A twofold problem for soybeans

Agronomists suggest growers think about managing sudden death syndrome and soybean cyst nematode together.

October 25, 2017

4 Min Read
SDS SYMPTOMS: Yellowing of leaves followed by tissue turning brown usually doesn’t appear until favorable conditions trigger upper-canopy leaf symptoms. There’s a strong correlation between sudden death syndrome and presence of soybean cyst nematode in a field.

Soybean growers in Iowa have been battling sudden death syndrome for at least 10 years. It’s a tricky challenge. Even fields that are impacted by the disease might not show symptoms until late in the season. Although the fungus infects seedlings early, foliar symptoms — yellowing of leaves, followed by brown tissue — typically don’t appear until favorable environmental conditions trigger upper-canopy leaf symptoms during reproductive growth stages.

While it’s important to scout for SDS symptoms, managing the disease requires digging a little deeper to find out what increases the chance of development and then taking action ahead of time.

A warning sign for SCN
Cool and wet conditions early in the season are often thought to increase a primary fusarium root infection; however, weather isn’t the only contributing factor. University research shows a strong correlation between SDS and the presence of soybean cyst nematode a field. Even if growers don’t think or know that they have SCN in their fields, foliar symptoms of SDS should be a warning sign to test the soil for SCN.

Why? SDS itself remains at the root level and in the stem closest to the soil where SCN also infects the plant.

“Juvenile nematodes create wounds in soybean roots, which allows the fusarium fungus to infect the plants,” explains Dale Ireland, seed care technical product lead at Syngenta. SCN makes it easier for SDS to not only infect the plant, but also develop earlier than when SCN isn’t present. The early onset of disease pressure makes plants even more vulnerable to stunted development during their critical early-growth stages.

Additionally, the season-long stress caused by SCN compromises the plant’s defense system.

“Plants infected by SCN exhibit more severe SDS symptoms when the nematode is present,” says Greg Tylka, Iowa State University Extension nematologist.

Managing SDS, SCN together
In order to get the most yield out of soybeans, Syngenta agronomists advise growers to think about managing SDS and SCN together. Since there are no in-season treatment options for either pathogen, SDS and SCN management should begin early. In addition to adopting cultural practices, such as a non-host crop rotation, growers should regularly sample their fields for SCN to prepare for the potential threat.

Because SCN and SDS are so widespread, Syngenta agronomists recommend growers start their seasons by planting soybean varieties with genetic resistance to both pests. NK soybean varieties offer a premier selection of products with industry-leading SDS tolerance, as well as SCN resistance, says Ireland.

Developed using advanced research and technology, NK soybeans deliver elite genetics and protect against a range of damaging pests and diseases, he adds. They offer the industry's best SDS ratings when compared to major competitors' varieties, with an average 1.5-point advantage on a 9-point scale.

In fields with known SCN pressure, a seed-applied nematicide is also recommended. Tylka says seed-applied nematicides may provide some added protection in fields where the performance of SCN-resistant soybean varieties is declining.

Clariva Elite Beans seed treatment offers season-long SCN protection and helps reduce the impact of both SCN and SDS, says Ireland. The addition of Mertect 340-F fungicide applied with Clariva Elite Beans helps to further protect high-value seed with added SDS protection. Mertect 340-F has shown consistent performance under SDS pressure in four consecutive years of testing in Syngenta trials.

Protecting future yield potential
Growers who had issues with SDS this year are at risk to see the pathogen again next year. SDS can overwinter in SCN cysts, increasing its ability to survive from one growing season to the next, according to Iowa State University Extension.

“The fusarium fungus can overwinter in the cysts, so as soon as the cysts hatch next spring, the possibility of SDS infection is more likely,” says Dean Grossnickle, Syngenta agronomy service representative based at Slater, Iowa. “It’s important to reduce SCN feeding and reproduction as much as possible. Compared to competitor seed treatments that only provide early-season protection, Clariva Elite Beans is the only seed-applied nematicide that offers season-long protection against SCN.”

As the No. 1 and most widespread soybean pest in the U.S., SCN can result in yield losses of up to 30%. Although less common than SCN, SDS can cause yield losses of up to 50%, depending on the severity of the outbreak. Growers can take back their yield and protect their future yield potential from SCN and SDS with proven management tools. If left alone, these top two threats are capable of building a destructive empire belowground that will continue to rob growers of their yield.

Source: Syngenta



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