Production Blog

DECATUR, Ill. (DTN) -- "Come see a real, live nematode!"

Several decades ago, I was working at a farm show where an exhibit featured a carnival barker attempting to attract those walking by into their exhibit. Soybean cyst nematode (SCN) isn't exactly in the category with the largest snake or a three-headed calf, but at the time, the pest was relatively new and loomed ominous despite being nearly invisible to the eye.

"Come see a real, live nematode!"

Over the years, this barker chant has become like an earworm in my brain because I've often wondered if farmers would take the pest seriously if they could "see" stealthily robbing yields and profits. Fact is, you can "see" them if you do a little digging this time of year.

Iowa State University plant pathologist Greg Tylka's blog post this week was a good reminder that looking for adult females of the SCN on roots of young soybean plants is an easy and effective way to check fields for this yield-reducing pest.

"The moment a soybean field is planted, the clock starts ticking on when the first new egg-filled adult SCN females of the year will appear on the surface of roots. Generally, it takes about four weeks for nematodes to infect and develop into adult females, but SCN females have been seen on roots in Iowa as soon as 26 days after planting," he wrote.

In 2018, warm weather early in May encouraged early development of SCN females. Read more about that here: https://crops.extension.iastate.edu/….

In 2024, the slower pace of soybean planting in many areas may spread out the timetable. But the message remains the same: Get ready to dig. SCN is overcoming the varietal resistance we've come to depend on for years. Seeing the presence of females (called cysts once they die) is a clue further testing is needed.

SIMPLY DIG IT

The procedure to look for SCN females on roots is as simple as putting boots in the field and shovel in the soil. Dig soybean roots from the top 12 inches of soil with a spade or shovel, do not pull them out of the soil. Gently shake the soil from the roots. If soil adheres to the roots, crumble the soil away with your fingers, Tylka advised.

SCN females will appear as small, white or light yellow, round objects on the soybean roots. On average, the females are about the size of a period in a printed sentence, and most people can see them with an unaided eye. They are much smaller and lighter in color than nitrogen-fixing nodules that appear on healthy soybean roots.

All SCN females do not emerge at the same time, they slowly appear over many days. Females can be seen on roots dug from soil through late summer because a new generation of SCN occurs every 28 days.

The bugaboo with SCN is it doesn't always give obvious symptoms of damage above ground. There is nothing that can be done during the season to manage SCN. But these mid-season looks are a good time to litmus test to see if SCN-resistant soybean varieties and the nematode-protectant seed treatments are still working.

WHERE TO DIG IT

While soil testing a field for SCN on my home farm last fall, I realized how big the field can be. Field entryways where soil from other fields can get introduced by machinery is a good place to start, Tylka noted. Places you've noticed yields have dipped is another place to dig. To read his entire blog on the topic go to: https://crops.extension.iastate.edu/….

DTN and Progressive Farmer partnered with The SCN Coalition (https://www.thescncoalition.com/…) to dig deeper into testing for the pest and what to do with those test results. Watch for the series "Stomp on SCN Yield Losses" DTN has begun to run.

The first story, " Take an HG Type Test to Avoid Varieties Vulnerable to Soybean Cyst Nematode," can be found at https://www.dtnpf.com/….

You can find the second of our three-part series, "Consider These 5 Steps When SCN Threatens to Reduce Soybean Yields," on our DTN products on June 17. You can also find the complete SCN package of stories in the Summer issue of your Progressive Farmer magazine.

Pamela Smith can be reached at pamela.smith@dtn.com

Follow her on social platform X @PamSmithDTN

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