Sampling fields for soybean cyst nematodes (SCN) is a task that should be on every farmer’s fall to-do list along with the many other chores needing done before winter sets in.
Samples should be collected from corn fields after harvest to learn what SCN population densities await next season’s soybean crop. Soil samples should also be collected from fields of harvested soybeans this fall to determine if SCN was present and what effect they might have had on soybean yields in 2022.
Reproduction of the nematode is greatest in dry years, and SCN egg numbers were high in the fall of 2021. Similarly high SCN numbers are expected again this fall.
The basics of sampling for SCN don’t change from year to year. The following guidelines are a repeat from last fall’s ICM News article reminding that fields should be sampled for the nematode.
- Use a soil probe, not a spade, to collect soil cores.
- Collect 15 to 20 soil cores eight inches deep from every 20 acres.
- Collect multiple-core soil samples from management zones in the field, if possible.
- Combine the soil cores from a sampled area in a bucket, break up and mix the cores well, and then fill a soil sample bag with mixed the soil.
Where to send samples for processing
The Iowa State University Plant and Insect Diagnostic Clinic processes soil samples for SCN egg counts. The cost is $20 per sample for in-state samples and $25 per sample for out-of-state samples. The Nematode Sample Submission Form is available through the Extension Store and provides details about where to send the samples.
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There also are numerous private soil testing laboratories in Iowa and surrounding states that process soil samples for SCN eggs. The SCN Coalition has a map of the names and locations of these labs online.
An Iowa State University Extension and Outreach publication, IPM 61, is available and provides guidance on how to interpret SCN soil sample results and compare results among different testing laboratories. Iowa State’s management recommendations based on soil sample egg counts in fields are available online also.
Once a field is known to be infested with SCN, an integrated approach to manage the nematode is recommended. Farmers should grow SCN-resistant soybean varieties in rotation with nonhost crops, such as corn, and consider using nematode-protectant seed treatments on soybeans.
Soybean varieties with PI88788 resistance have lost much of their effectiveness in Iowa and surrounding states because SCN populations have become resistant to PI88788 resistance. Farmers should look for and grow resistant soybean varieties with the hard-to-find Peking resistance, which is very effective against SCN populations in most Iowa fields, providing high yields and suppressing nematode reproduction.
There are not enough varieties with Peking SCN resistance for everyone to use, so farmers also should seek out and grow varieties with PI88788 resistance that provide high yields and good SCN control. Such information is available at Iowa State’s SCN-resistant Soybean Variety Trial Program website and may be available from other university and commercial information sources as well.