Plant-Parasitic and Free-Living Nematodes from Organically Farmed Fields in Illinois and Wisconsin

Plant-parasitic nematodes feed on soybean roots resulting in potential yield losses. Surveys of nematodes in certified organic soybean fields have been infrequent compared with surveys in nonorganic soybean fields. We conducted a nematode survey from certified organic soybean fields in northern and central Illinois and southern Wisconsin to determine the frequency and population densities of plant-parasitic and free-living nematodes. Fields surveyed included both long-term (with soybean planted every fifth year or longer in the rotation) and short-term (with soybean planted every third year in the rotation). A total of 27 composite soil samples, each consisting of multiple cores to a depth of 20 cm, were collected from 14 fields in 2019. Common plant-parasitic nematode taxa included spiral (Helicotylenchus spp.), lesion (Pratylenchus spp.), cyst (Heteroderidae), stunt (Tylenchorhynchus spp.), dagger (Xiphinema spp.), and pin nematodes (Paratylenchus spp.). Among the taxa, spiral, lesion, and dagger nematodes were above previously reported damage threshold levels in some fields. From the summer season-sampled soils, cyst nematode population densities and nematode abundance were significantly higher and lower, respectively, from fields under short-term versus long-term rotation with soybean. From the fall season-sampled soils, the structure index but not the other diversity and community indices of free-living nematodes were significantly higher from fields under long-term versus short-term rotation with soybean. Overall, these results provide evidence for the occurrence of plant-parasitic and free-living nematodes from organically farmed soybean fields in Illinois and Wisconsin that varied in rotation length.