We have had some amazing fall weather so far this year. It is hard to believe that winter is just around the corner. One productive way to enjoy the fall weather, while it lasts, is to collect soil samples to test for the soybean cyst nematode (SCN).
Reasons to sample for SCN
Fall is the best time to sample for SCN. Samples can be collected from harvested cornfields that will be cropped to soybean in 2016 in order to check if SCN is present. And samples can be collected from harvested soybean fields if yields were disappointingly low this year with no apparent cause. Finally, results of soil samples collected from fields with known SCN infestations will provide feedback on how well management practices have been working at keeping SCN numbers in check.
Collecting soil samples to check for SCN is not difficult. A few simple guidelines to follow are:
- It is best to use a soil probe, not a spade, to collect soil cores.
- Collect soil cores to a depth of 8 inches.
- The more soil cores collected from the smaller the area, the more accurate the results will be. Collecting 15 to 20 soil cores from every 20 acres often is recommended.
- Combine all soil cores in a bucket and mix them well before placing the mixed soil into a soil sample bag.
- Most private soil-testing labs in Iowa can process samples for SCN.
- SCN samples also can be sent to ISU’s Plant and Insect Diagnostic Clinic, room 327 Bessey Hall, Iowa State University, Ames, IA 50011.
Figure: Example of a sampling pattern in a field with different management zones. Each “x” represents the location at which a soil core was collected.
Management options, if SCN is found
It would not be surprising to discover SCN in any field in Iowa in which soybeans have been grown. SCN is widely distributed in the state, and once an SCN infestation becomes established, the nematode can survive for ten or more years without a soybean crop being grown.
Managing SCN should involve coordinated use of multiple tactics, including growing nonhost crops (such as corn), growing SCN-resistant soybean varieties, and using nematode-protectant seed treatments when soybeans are planted. Also, it is very important to grow SCN-resistant soybean varieties with different sources of resistance in successive soybean crops, if possible, but there are few resistant soybean varieties available with a source of SCN resistance other than the common PI 88788 resistance.