Fall is a great time to sample soil for soybean cyst nematode


With harvest complete or wrapped in some areas of the Corn Belt, now is the time to take samples for soybean cyst nematode (SCN).

The pest is widespread throughout Iowa and much of the Midwest, says Greg Tylka, a nematologist at Iowa State University Extension. He adds that most resistant soybean varieties grown for decades to maintain profitable yields and control SCN counts (resistance based on PI88788) have lost much of their effectiveness. In addition, SCN reproduction was likely much higher than normal in fields where soybeans were grown in 2021 due to the hot, dry growing season, making matters worse, he says.

SCN quickly began to spread in Missouri in the 1970s and gained a foothold in most soybean counties in the state by the 1990s. SCN is easily transported in the soil; cysts and eggs are spread by equipment, water or wind. It is essential to test the soil before planting soybeans, according to Kaitlyn Bissonnette, extension plant pathologist at the University of Missouri (MU). CNS is the # 1 disease of soybeans in the United States and Canada, with yield losses of up to 30% per infected acre. Symptoms include stunted growth and yellowing, but yield loss can occur even without visible symptoms, Bissonnette explains. She advises sampling for the SNA every three to five years.

Sampling guidelines

Samples taken from fields where soybeans were grown in 2021 will reveal if SCN is present and at what level, Tylka says.

Sampling of fall fields slated for soybean production in 2022 will provide information on soybean yield potential in those fields next year. Soil samples can be taken any time after harvest until the ground freezes or is covered with snow.

Tylka advises farmers to:

  • Use a soil probe, not a shovel, to collect the soil cores.
  • Collect 15 to 20 cores of soil 8 inches deep for every 20 acres.
  • Collect multi-core soil samples in field management areas, if possible.
  • Combine the 15-20 cores from a sampling area in a bucket, break and mix the carrots well, then fill a soil sample bag with the mixed soil.

Where to send samples

In Iowa, the Iowa State University Plant and Insect Diagnostic Clinic processes soil samples for the count of SCN eggs. 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 Extensions Store and provides details on where to send the samples.

There are also many private soil testing laboratories in Iowa and surrounding states that process soil samples for SCN eggs. The SCN Coalition has a map of names and places of these online labs.

Missouri farmers can submit two free SCN tests by contacting their county University of Missouri Extension Center or the SCN diagnostic laboratory, said Bissonnette.

The United Soybean Board Levy Dollars are funding up to two free tests for Missouri farmers as part of the SCN Coalition’s efforts to raise awareness of the SCN. The SCN Coalition is a public-private partnership of academic researchers, extension specialists and industry representatives.

For more information, Missouri farmers can contact their local MU extension center or SCN diagnostic lab at [email protected] or 573-884-9118. Examples of submission forms Are on the SCN diagnostic website.

SCN management

Once a field is known to be infested with SCN, an integrated approach to managing the nematode is recommended, explains Tylka. Farmers should grow SCN resistant soybean varieties in rotation with non-host crops, such as corn, and consider using nematode protective seed treatments on soybeans. Soybean varieties resistant to PI88788 have lost much of their effectiveness because SCN populations in Iowa and surrounding states have become resistant to resistance to PI88788, Tylka explains. Farmers should research and grow resistant soybean varieties with Beijing’s uncommon resistance, which is highly effective against SCN populations in most fields in Iowa, providing high yields and suppressing nematode reproduction.

There aren’t enough SCN resistant varieties from Beijing for everyone to use, so farmers should also look for PI88788 resistant varieties which are known to provide high yields and good SCN control, explains. Tylka. This information is available on Iowa State SCN-Resistant Soybean Variety Testing Program Website.

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