Red, white and blue are the colors of patriotism in the U.S., but a new map showing the presence of soybean cyst nematode (SCN) uses those colors in an altogether different way.
Soybean growers can take a quick look at the map, provided by the SCN Coalition, to tell whether they are in an area potentially at risk. Specifically:
Red shows the counties in each state where SCN has been found.
Blue signals the newest counties or areas the pest has moved into.
White indicates counties or areas where SCN has not been confirmed – but they aren’t necessarily SCN-free.
Some states have SCN in every county. Consider the top two soybean producing states:
- Illinois has SCN in all 102 of its counties and 88% of all soybean fields.
- Iowa also has SCN in all 99 of its counties and at least 70% of all soybean fields.
“I tell my farmers there’s a three out of four chance any field they grow soybeans in has SCN,” says Greg Tylka, director of the Iowa Soybean Research Center at Iowa State University.
He says fields with low levels of infestation might show very few symptoms of damage, but it becomes more pronounced as populations climb.
“There’s stunting and there’s yellowing, but it won’t be uniform in the field. It’ll be patchy,” he says. “Some indirect symptoms include areas of a field with poor weed control. The soybeans might not look sick, but because of poor weed control they are stunted and the plants don’t close over as quickly.”
How Prevalent Is SCN?
In 2021, Pioneer tested 439 soybean fields in Illinois, Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Ohio and Wisconsin to determine SCN pressure. The company reports SCN infestations were found throughout the study area, with over 80% of fields sampled having some level of SCN infestation.
Furthermore, 27% of fields sampled had SCN population levels capable of causing heavy to severe crop damage.
Tylka says many farmers don’t even realize they have SCN, which can make it a silent yield robber.
“We can have up to 30% yield loss without any loss of color of the plants, height of the plants or weight of the leaves. When you get into severe situations where you can see even mild stunting, or mild yellowing, it goes up from there. Simple math shows with a 30% loss on 70 bu. beans that’s 21 bu. With $10 soybeans that’s $210 per acre,” he explains.
Spring Soil Test To ID The Pest
Farmers need to soil sample and have a diagnostic laboratory test specifically for SCN and determine the population level present in the soil – a practice that can still be done this spring and even during the growing season.
According to the SCN Coalition, some state soybean boards offer free SCN testing. This changes from year to year, but in the past such states offering free SCN testing have included Michigan, Nebraska, North Dakota, South Dakota and Wisconsin.
Once detected, farmers can use an integrated management plan, which includes varietal selection, crop rotation and a seed treatment.
“Farmers should rotate to corn because corn is a non-host crop,” Tylka adds. “Any year a farmer grows corn in a field, SCN egg numbers will drop; some of the eggs are going to hatch out and the little worms are going to starve. That drop can be as little as 5% or 10% to up to 50%, so corn is our best tool to lower numbers.”
Tylka says an excellent resource for farmers is the Soybean Cyst Nematode Management Guide originally published by the SCN Coalition and recently updated and reissued by the North Central Soybean Research Program. The fifth edition is available to read or print in pdf format.
Interviews by national reporter Michelle Rook contributed to this article.
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