By Bruce Potter - Extension IPM Specialist
The soybean cyst nematode (SCN) is a serious pest of Minnesota soybean and has been managed with crop rotation and soybean varieties with resistance to SCN. This approach is becoming less effective, however, because SCN populations virulent on (able to reproduce on and damage) SCN resistant soybeans are increasingly widespread. A seed treatment biological (Clariva™ Complete, Syngenta Crop Protection®) has been labeled for management of SCN.
The Minnesota Soybean Research and Promotion Council funded a 2014-15 project to provide geographically and environmentally robust data on the potential efficacy of Clariva for SCN management. One objective of this study was to evaluate the effects of this biological nematicide and other fungicide plus insecticide treatments on soybean yield, including potential interactions with SCN host plant resistance, environment, and an insecticide plus fungicide combination. A second objective was to determine if Clariva affects SCN reproduction.
Seed treatments compared, in order of decreasing complexity and cost, were: Clariva® Complete™ + Mertect® fungicide, Clariva® Complete™, Cruiser Maxx® + Vibrance™ fungicide (an insecticide/fungicide counterpart to Clariva Complete without the Clariva), Cruiser Maxx®, or untreated seed. At each of eleven locations, seed treatments were evaluated on a variety with PI 88788 source SCN resistance and on a susceptible variety.
The 2015 results were similar to those observed in 2014. Variety selection has an impact on yield and SCN reproduction. Resistant varieties performed better than susceptible varieties under significant SCN population pressure.
In one of the eleven 2015 study sites, seed treatments yielded significantly more than untreated seed. At this site, treated seed yielded more than the untreated check and all seed treatment combinations yielded similar. The addition of Vibrance fungicide, Clariva nematicide, or Mertect fungicide did not increase yield above that of Cruiser Maxx, the base fungicide plus insecticide. Unlike the 2014 results, when the 2015 data was analyzed across all sites, the group of seed treatments yielded more than untreated seed, but only for the SCN resistant varieties. Again, there was no yield benefit for adding the nematicide or additional fungicides over the base fungicide plus insecticide treatment.
These results indicate that the decision to use soybean seed treatments as a production input should be evaluated carefully. They also reinforce the importance of preserving the effectiveness of SCN resistant varieties.