"We have had some amazing fall weather so far this year," notes Greg Tylka, Iowa State University Extension plant pathologist and nematologist. "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 presence of soybean cyst nematode in your fields." Tylka provides the following guidelines to sample fields for SCN.
Good reasons to sample for SCN. Fall is the best time to sample for SCN, he says. Soil samples can be collected from harvested cornfields that will be planted to soybeans in 2016 in order to check if SCN is present, and if so, at what population levels. Send the samples to a soil testing lab, have them tested and see what the results tell you.
Should you collect soil samples from harvested soybean fields this fall? Samples can be collected from harvested soybean fields if yields were disappointingly low this year with no apparent cause, says Tylka.
Results of soil samples collected from fields with known SCN infestations will provide feedback on how well your management practices have been working at keeping SCN numbers in check.
Follow these soil sampling guidelines. Collecting soil samples to check for SCN is not difficult, says Tylka. 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 is often 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. Soil samples for SCN testing also can be sent to ISU's Plant & Insect Diagnostic Clinic, Room 327 Bessey Hall, Iowa State University, Ames, IA 50011.
Management options, if SCN is found in your field
"It would not be surprising to discover SCN in any field in Iowa in which soybeans have been grown," says Tylka. "SCN is widely distributed in the state, and once an SCN infestation becomes established, the nematode can survive for 10 or more years in a field without a soybean crop being grown in that field."
Managing SCN should involve coordinated use of multiple tactics, he advises. That includes crop rotation, growing non-host 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," says Tylka. "But when choosing a soybean variety to plant keep in mind there are few SCN resistant soybean varieties available with a source of SCN resistance other than the common PI 88788 resistance."
Sample now, before planting next year's bean crop
Soil samples can be collected throughout the fall, until a significant snowfall or a hard freeze occurs, he adds. The equipment you need for sampling soil is the same equipment you use for taking a soil sample for nutrient analysis: a soil probe, a bucket and a plastic or plastic-lined soil bag.