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Soybean Cyst Nematode Distribution in North Dakota (5/11/17)

Since 2013, over 2,200 soil-samples have been submitted as part of a state-wide survey for Soybean Cyst Nematode (SCN).

Soybean Cyst Nematode Distribution in North Dakota

Since 2013, over 2,200 soil-samples have been submitted as part of a state-wide survey for Soybean Cyst Nematode (SCN). The program is funded by the North Dakota Soybean Council and operated by the North Dakota Extension Service. Approximately 1/3 of these samples have been positive and approximately ½ of those have been higher than a ‘low level’ (gray boxes). Positives have occurred primarily in the Southeastern part of the state, but SCN is clearly being detected in other locations. However, growers should be aware that some of these results are likely to be false positives.

Several very important points about the results are below.

1) How egg counts are determined?

Data points are nematode egg counts, presented as eggs/100cc of soil (100cc of soil is roughly 3-4 ounces). Egg counts are determined by extracting eggs from the soil and visually counting eggs through a microscope.

2) Low egg counts could be false positives.                                                                                         

It is nearly impossible to differentiate SCN eggs from the eggs of other closely related nematode species. Consequently, a soil sample positive for low egg counts (gray boxes) could be reflective of other nematodes in the soil, and doesn't necessarily mean the sample positive for SCN eggs. To a lesser degree, some green triangles could be false positives too, as the range goes from 201-2,000. I am suspicious of the two green triangles in Ward and Mercer counties – they were both on the low end of the green range.

3) Zeroes could be false negatives.

During the extraction process nematode eggs can be lost, which may result in a false positives. Additionally, SCN is notoriously patchy in a field and may be missed in the sampling process.

4) What level causes yield loss?

Under favorable conditions (which include high pH, lighter soil, a warm and dry growing season) yield loss can begin to occur at any egg level. This is primarily because SCN can undergo 2-3 life cycles in a single growing season, and with each cyst producing 100-200 eggs, egg counts can increase very quickly and quite dramatically. We believe that when numbers are 10,000 or greater (yellow boxes and red pentagons) even resistant varieties will experience significant yield loss.

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Sampling in 2017.

The North Dakota Soybean Council will be funding this sampling program again in 2017. Up to 2,000 sample bags will be available at County Extension offices beginning in mid-August (sampling at the end of the growing season is the best time to detect SCN). We will provide more information on the sampling program, detecting and managing SCN as the season progress.

We thank the North Dakota Soybean Council for funding this program, the many Extension agents who operate the program, Agivse for sample processing, and all the growers and agriculture professionals who submitted samples.

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Sam Markell

Extension Plant Pathologist, Broad-leaf Crops

 &

 Guiping Yan

Plant Nematologist


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