By Sam Markell
Extension Plant Pathologist
Soybean cyst nematode can cause 15-30% yield loss before any above ground symptoms appear and we know that it is spreading in North Dakota. Whether or not you take advantage of the North Dakota Soybean Council sampling program, we encourage soybean growers to sample for SCN. Below are some quick facts about SCN and SCN sampling.
Q: Where is SCN in North Dakota?
A: SCN has been confirmed in 19 counties and it is likely in other counties as well. The highest egg levels have been reported in Richland, Cass and Traill Counties.
Q: What’s the most common symptom of SCN?
A: Healthy looking soybeans. Typically, the first thing you will notice is a spot in the field that doesn’t yield well. After you have relatively high egg levels in a spot, you may start to see stunting or yellowing that appears in August.
Q: When is the best time to sample?
A: Just before or after harvest. The nematode population builds through the season, so sampling at the season ends maximizes your chances of detecting it.
Q: Where do I sample?
A: Anything that moves soil can move SCN. Consequently, we tend to find SCN in places where soil is deposited from other sources, such as the field entrance (soil moves on equipment), low spots (from overland flooding) or shelter belts / fences (from wind-blown soil). Additionally, consistently low yielding patches or yellow spots that appear in August may be a result of SCN. Lastly, SCN likes high pH; if you have a low yielding and yellowing high pH spot, it could be SCN.
Q: How do I sample?
A: Use a small soil probe or a shovel and aim for the roots. Take 10-20 small samples, mix up, and fill soil bag with the composite sample. Keep the bag relatively cool and get to the lab in the next few days.
Q: What do the results tell me?
A: Your results will be reported in eggs / per 100cc of soil. Essentially, this is how many eggs you have in about half a cup of soil. Positive egg counts mean you should begin managing SCN, negative egg counts mean you should be happy, and sample again when you put soybeans back in the ground. One point of note, very low numbers could be false positives (50 or 100). Resampling may be a good idea.