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Soil-test postharvest to identify presence of soybean cyst nematode

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Is soybean yield not quite what you expected for some fields? Are the disappointing fields repeat offenders? Your past yield maps may be trying to tell you something. Soybean cyst nematode (SCN) could be the culprit, and there’s one sure way to find out if it could be plaguing your acres.

Start with accurate identification.
SCN affects a wide variety of soil types, and typically an environment conducive to good soybean yield is also conducive to SCN reproduction.

As soon as SCN become established, the problem is permanent. And to make matters worse, SCN are easily transferred by tillage equipment, surface water, wind and animals. Even low levels of SCN can cause yield reduction, and it is then that the telltale visual symptoms — stunting and yellowing — are not obvious. Even when such symptoms are present, the observations are often associated with other issues, such as nutrient deficiency, soil compaction, drought stress or other diseases. Scouting for cysts on roots can be helpful in season, but the most conclusive and effective way to determine presence of SCN and level of pressure is through soil testing. 

Soil testing tips.
After harvest yet before the ground freezes is the best time to gather soil samples. Sampling in the spring is also feasible but leaves less time to make management decisions.

Before getting started collecting samples, you’ll need a bucket, soil probe and collection bag. The following steps will ensure soil samples are taken accurately and are representative of an entire field:

  • Insert the soil probe into the root zone at an angle, 6 to 8 inches deep. One sample should represent no more than 20 acres.
  • Collect soil core samples from at least 20 locations randomized throughout the field.
  • All core samples should be placed in the same bucket, crushed and mixed together. Transfer the mixture to a soil sample bag and fill to the line, generally about a quart of soil.
  • Fill out all the required information on the sample bag including: contact information, number of acres represented by the sample and cropping history, including most recent crop. Seal tightly.
  • Mail to a certified lab for analysis and results. Results are generally reported by number of cysts or number of eggs per cubic centimeter.

If SCN is confirmed in a field, egg counts should be checked every six years, according to the University of Nebraska, to monitor changes in populations and evaluate management practices.

SCN best management practices for containment.
Finding the right combination of SCN management tools is essential for profitable soybean production. Rotation to nonhost crops for six years is an effective management tool for keeping populations at bay, but not necessarily a realistic strategy for most. Planting SCN-resistant varieties can be an effective tool as well, and chances are, the beans you are currently planting have a source of resistance: PI 88788. If that is the case, considering seeking out varieties bred with a different source of SCN resistance, such as Peking. Nematicide seed treatments can also be a helpful management tool.

Lastly, planting SCN-infected fields last can help minimize spread. Diligent cleaning of tillage equipment before moving to a different field can also help minimize SCN movement. 

For information specific to SCN-resistant soybean varieties, visit https://crops.extension.iastate.edu/cropnews/2018/11/fewer-more-diverse-choices-scn-resistant-soybean-varieties-iowa-2019.

For answers about SCN in your specific fields and soil types, please contact your agronomic pest adviser or ag retailer.

Soil-test postharvest to identify presence of soybean cyst nematode

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