Abstract
The prevalence of Heterodera glycines and other cyst and vermiform genera was determined from 8,009 soil samples over two decades. Prevalence of cyst nematodes for farms increased from 16% in 1998 to 1999, reaching a peak of 40%, with marked differences among Wisconsin's nine agricultural districts in how much the odds of a positive test increased. Estimates at the sample scale also increased over time but peaked at 29%. Assay of all nematodes beginning in 2012 showed Pratylenchus, Helicotylenchus, and Xiphinema to be more prevalent in Wisconsin soybean fields than cyst nematodes. Prevalence estimates for Pratylenchus and Helicotylenchus for soybean and rotation crops ranged from 76 to 89% and 58 to 83%, respectively. Species identification of Pratylenchus from a subset of the samples revealed six species. The majority of cyst-positive samples were infested with Pratylenchus, and count data showed that the number of cyst eggs and juveniles per 100 cm(3) soil was 60% lower in samples positive for Pratylenchus. The influence was reciprocal, as Pratylenchus population densities were 41% lower in samples positive for cyst nematodes, suggesting a competitive interaction. The Wisconsin soybean nematode testing program provides a useful model for estimating nematode prevalence using citizen-based surveys.