On-Farm Evaluations of a Seed Applied Nematicide on Soybeans.

The soybean cyst nematode (SCN) is a plant-parasitic nematode that can cause significant yield loss in soybean (Glycine max). The objective of this study was to evaluate the efficacy of the seed treatment Clariva to control SCN and its effect on yield. Thirty on-farm replicated strip trials in northern Iowa and 18 small-plot experiments across Iowa were conducted in 2014 and 2015. The two treatments, Clariva Complete Beans – CruiserMaxx Advanced plus Vibrance plus Clariva (Clariva) and CruiserMaxx Advanced plus Vibrance (CruiserMaxx), were applied to SCN (PI88788) resistant or moderately resistant soybean varieties. Clariva contains the bacteria Pasteuria nishizawae which is parasitic to nematodes. The mid-season SCN soil sampling for the strip trials was done in June of both years and for small plot trials at planting, mid-season, and harvest. Plant stand counts were collected mid-season. The georeferenced yield data were collected only for the on-farm strip trials. In 2014, the average yield difference between Clariva and CruiserMaxx treatments was 13.5 kg ha^-1 (90% CI from -40 to 74 kg ha^-1) across small-plot trials and 53.5 kg ha^-1 (90% CI from 21 to 94 kg ha^-1) across on-farm strip trials. A significant reduction of 49% in season-long SCN reproduction comparing beginning- and end-of-season SCN soil population densities associated with Clariva vs CruiserMaxx was observed in small-plot trials in 2014. A greater yield did not always occur with Clariva in locations where significant reductions in SCN reproduction were detected. For the combined dataset of two types of trials, Clariva produced a relatively small but significant yield increase of 40 kg ha^-1 (90% CI from 5 to 72 kg ha^-1). The 2015 study will determine the consistency and predictability of Clariva treatments on yield response and SCN reproduction in different environmental conditions.