Adapted from article by Dr. Anne Dorrance, OSU Plant Pathology, C.O.R.N. 2020-36
The Soybean Cyst Nematode (SCN) is an invasive species has adapted quite well to Ohio conditions, and is unfortunately doing very well in some fields based on egg counts. We are wrapping up intensive sampling of Ohio Fields from the support of the soybean check-off through Ohio Soybean Council and United Soybean Board. To date, 566 samples were submitted from 34 counties. From these, 33.7% had populations of 200 eggs or more. There were 7.6% in the high range (>5,000 eggs per cup of soil), which are associated with significant yield losses.
More importantly, from these samples that had high numbers, we have completed the SCN Type test. This evaluates which resistance will be effective, PI 88788 or Peking. From the 56 SCN populations (each from a single field), only 7 populations were still controlled by PI 88788. The remaining populations could reproduce on the soybean roots of the PI 88788 source of resistance, albeit at levels of 30 to 60% of the susceptible.
Remember that SCN resistance mechanism is by means of reduction in reproduction to less than 10% of a susceptible variety. Peking fared better in the test, where almost half of the populations, it was very effective and where it could reproduce it was primarily in the 10 to 30% range of reproduction compared to susceptible. What this would look like in a field is the egg counts would show a slow steady climb when planted to soybeans, and not the reduction in numbers like we would expect if the resistance was effective.
We still have some samples to complete, but overall SCN is best managed when the population levels (based on egg or cyst counts) in a field (overall numbers) are kept low. This is done through rotating crops to a non-host crop, managing weeds that can serve as hosts (including some cover crops) and protecting the overall health of the plant through the growing season. As you select varieties for this next year – PI 88788 resistance will provide some protection; but watch your egg counts and your yields. Check the county average – was this field lower? On your yield maps are there areas that are consistently underperforming without any explanation? If they are large or you know you have a high SCN population, after you plant corn or hopefully wheat for 2021– go back into that field with a different type of resistance such as Peking to keep driving the numbers down.