Multi-location evaluation of fluopyram seed treatment and cultivar on root infection by Fusarium virguliforme, foliar symptom development, and yield of soybean

A study was conducted in five American states and Ontario, Canada, in 2015 and 2016 to determine the effects of fluopyram seed treatment and cultivar on the root rot and foliar phases of sudden death syndrome (SDS) of soybean. Three seed treatments were evaluated: (1) base treatment (control) containing prothioconazole + penflufen + metalaxyl (0.019 mg a.i./seed) + metalaxyl (0.02 mg a.i./seed) + clothianidin + Bacillus firmus I-1582 (0.13 mg a.i./seed), (2) base treatment + fluopyram (0.15 mg a.i./seed), and (3) base treatment + fluopyram (0.075 mg a.i./seed). Three soybean cultivars, categorized as susceptible, moderately resistant and resistant were planted at each location. Both rates of fluopyram reduced root rot and foliar disease index (FDX) and increased yield compared with the base treatment. The two rates of fluopyram did not differ for reducing root rot or FDX, but yield was greater with the higher versus lower rate. Fluopyram reduced root colonization by Fusarium virguliforme as measured with quantitative PCR in one of two study years. Yield was not correlated with root rot at the V2, but was negatively correlated with root rot at the R4/R5 growth stage and with FDX. Root rot at R4/R5 was positively correlated with FDX. A yield benefit to fluopyram was found in a location where root rot but no foliar symptoms were observed. These findings suggest that fluopyram seed treatment can reduce the root rot and foliar phases of SDS, and both phases play an important role in yield and should be managed accordingly.