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Test for SCN to beat the pest


September 17, 2020
By OMAFRA Field Crop News team

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Soybean harvest has begun, and many growers have asked if they could sample for soybean cyst nematode this fall. For many growers, managing soybean cyst nematode (SCN) means planting resistant varieties. But effective SCN management does not end when you have selected your soybean varieties. It is imperative to know not only your SCN population levels in each of your fields, but also what is happening to those levels over time. It all begins with SCN soil testing!

If your SCN levels are decreasing, this could indicate your management program is working. If your SCN levels are rising, this is a big red flag that the problem is getting worse. It could get out of hand and cost you significantly in lost yield, dollars and sleep! If you do not know what is happening to your SCN population levels in your fields over time, your efforts may be wasted. One of the most important decisions a producer can make concerning this devastating pest is to take a SCN soil test.

Fall is a perfect time to sample harvested soybean fields or those which will be planted to soybeans in 2021. Sampling for SCN after or at harvest provides a perfect opportunity to test, since it’s typically a time when soil samples are taken to determine next year’s fertilizer program. It’s as simple as taking a few more soil cores from the field, mixing them together, splitting the sample and sending half for your fertilizer recommendations and the other half for SCN analysis. Fall sampling also helps identify poor-yielding fields or areas within the field that need sampling while they are fresh in your mind. A fall sample takes into account any significant SCN population changes that have occurred during the growing season.

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Remember, the results of the test are only as good as the soil sampling technique. Therefore, it is necessary to obtain a soil sample that is representative of the field. Ideally the numbers of acres in any one sample should not exceed 20 to 25 acres.

When you get your test back what does it mean? First, it lets you know if you have SCN and what the potential yield loss risk is for the field. If you get a “Not Detected” result, this means SCN is not present, is below detectable levels or – as is often the case – SCN levels are variable in the field and pockets were not captured in the sampling pattern. It does mean you should continue to monitor these fields since SCN levels can change rapidly.

Anything below 1,000 eggs/100 grams (g) of soil is considered low-risk, with a potential yield loss for susceptible varieties ranging from zero to 20 per cent; a resistant variety should be grown or the field should rotate to a non-host crop (corn/wheat). For moderate to high risk fields (1,000 to 10,000 eggs/100 g soil), potential yield losses range from 20 to 50 per cent, and SCN-resistant varieties will likely be affected, especially those containing the PI88788 source of resistance. Fields with over 10,000 eggs/100 g soil should be rotated to non-host crops for two years, then sampled again to determine if populations have declined sufficiently for soybeans. Susceptible varieties will see significant yield losses, as will those containing the adapted PI88788 population (SCN Type 2).

Although SCN cannot be eliminated, it can be beaten. The first step is identification, so get out there and sample. Take the test and beat the pest; know your number!

For more information please visit the SCN Coalition website at www.thescncoalition.com or OMAFRA Agronomy Guide Publication 811 at www.omafra.gov.on.ca/english/crops/pub811/p811toc.html).

For the full report, visit the OMAFRA Field Crop News website.