Soybean cyst nematode ranks as the No. 1 yield-robbing pathogen in the United States, and the only way to know whether it sits in a specific field is to pull a soil sample and send it to a lab.

SCN works quietly. It feeds on soybean roots, steals yield and often leaves no visible symptom above ground until populations are high. By the time plants show stunting or yellowing, the pathogen has usually already taken a bite out of the crop's potential. That is why testing matters more than scouting: the test, not the plant, is the diagnostic tool.

How should you collect a sample?

Sample the soil, not the plant. Nematode eggs and juveniles live in the root zone, so a probe or soil tube that reaches root depth captures what a surface scrape will miss.

The goal is representation. Move across the field in a systematic pattern — a zigzag or grid works — and pull multiple cores that together represent the area you want to manage. Bag the composite sample, label it clearly by field, and keep records of where each sample came from so results can be compared over time.

Consistency counts. Sampling the same fields the same way across seasons turns a single number into a trend, and trends drive management decisions far better than one-off readings.

What do the results mean?

Labs report SCN as egg counts, typically expressed per volume of soil. The interpretation hinges on the number: low counts still warrant attention, because SCN reproduces fast under susceptible soybeans and a modest population this season can become a heavy one two crops later. High counts demand an immediate change in strategy.

The result should feed directly into four decisions:

• Variety selection, rotating to soybean varieties with SCN resistance rather than susceptible lines
• Crop rotation, lengthening the gap between soybean crops with non-host crops such as corn
• Seed treatment choices, where nematode-protectant options fit the system
• Resampling schedules, to check whether populations are falling or climbing under the current plan

One caution shapes the whole exercise: resistance is not permanent. Repeated use of the same resistant varieties can select nematode populations that overcome that resistance, so egg counts that stay stubbornly high despite resistant beans are a signal to change tactics, not to repeat them.

Why test now rather than later?

Because SCN rarely announces itself, the test is the only early-warning system available. A field that tests negative or low buys time and keeps management cheap. A field that tests high explains yield gaps that weather, fertility and herbicide programs never fully accounted for.

Farmers should watch their sampling calendar next: build SCN testing into the routine soil-sampling cycle, and retest fields on a set interval to track whether rotations and resistant varieties are actually driving egg counts down.