Production Blog

The leading cause of soybean yield loss is easy to spot this time of year. All it takes is a shovel and a little digging to detect if soybean cyst nematode (SCN) is feeding in your field.

While SCN damage doesn't wave its hand in the way of visual above-ground symptoms, the females do start to appear on the soybean root surface about 4 to 6 weeks after planting. They remain visible for the remainder of the growing season.

A few years ago, I was invited to an in-field SCN learning session at Iowa State University. What surprised me was how easy the females were to spot on roots. They resembled white or light-yellow grains of salt or sugar and were easy to identify and were much smaller and lighter in color than nitrogen-fixing nodules that should also be present.

HOW TO DIG

Iowa State University plant pathologist Greg Tylka gives details about the best way to look for SCN females in a recent blog post. Find it here: https://crops.extension.iastate.edu/…

The main thing to remember is to dig the roots from the top 12 inches of the soil, do not pull. Gently shake the soil from the roots or crumble it away with your fingers. In general, the females are about the size of a period in a printed sentence. A hand lens or taking a photo with your phone and enlarging it can also be helpful in the search.

Tylka suggests starting your search in specific areas. SCN is like the neighbor's cattle--they may jump a fence to get into a field, but leaving the gate open is a sure invitation. In the case of SCN, field entrances are often where they first become established. Another good place to sample is in areas of the field that have shown lower-than-expected yields for no reason. Areas that have been flooded, have accumulated wind-blown soil or high pH are other prime locations to look, according to Tylka.

WHEN TO TEST

It's too late to do anything in-season to manage SCN but spotting SCN females this summer is affirmation of a need to test soil for the pest this fall.

"Mid-season is a good time to learn more about the hundreds of SCN-resistant soybean varieties and the several nematode-protectant seed treatments that can be used to help manage SCN in future years," Tylka noted.

"Whether or not you dig roots and see SCN females in fields this summer, plans should be made to collect soil samples to test for SCN in the fall if that hasn't been done in the past five years (or at all). Sampling a soybean field after harvest will provide the best assessment of the SCN situation and may help explain yields in the fields. Fall sampling of corn fields where soybeans will be grown in 2025 also is a good idea. Results of these fall samples will allow for time to plan management efforts for the next season if SCN is found," he wrote.

DTN and Progressive Farmer partnered with The SCN Coalition (www.thescncoalition.com ) to dig deeper into testing for SCN and what to do with those test results. To see more in the Stomp on SCN Yield Losses series:

-- "Take an HG Type Test to Avoid Varieties Vulnerable to Soybean Cyst Nematode," https://www.dtnpf.com/…

-- "Consider these 5 Steps When SCN Threatens to Reduce Soybean Yields," https://www.dtnpf.com/…

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

Follow her on social media platform X @PamSmithDTN

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