Evaluation of fungicides applied to early vegetative stage soybean for red crown rot control

Red crown rot (RCR) of soybean, caused by Calonectria ilicicola, is a significant soilborne disease that typically manifests during the flowering stages. Although seed treatments have been employed for RCR control, no method has been developed to provide protection throughout the entire soybean cultivation period. Therefore, we sought to evaluate the efficacy of fungicides applied to stems near the soil surface four weeks after emergence. Between 2022 and 2024, we conducted trials in soybean fields where RCR has occurred frequently, in Toyama Prefecture, central Japan. Identical field trials could not be repeated annually owing to the number of fields and the field size. Thus, data from different trials were integrated and analyzed using a network meta-analysis. The analysis revealed substantial heterogeneity and inconsistency for both disease incidence and a disease severity index derived from midpoint transformed severity scores. Contrastingly, yield showed low heterogeneity but significant inconsistency. Despite these limitations, all treatments efficaciously reduced disease severity. Additionally, most treatments improved the yield. Fluopyram (2.09 kg a.i./ha) applied twice and pydiflumetofen (0.92 kg a.i./ha) applied twice exhibited especially strong effects against disease severity compared with the non-treated control, with mean differences of –52.060 and –50.191, respectively. These findings suggest that further investigation of the optimal application methods and timing could facilitate the development of a comprehensive RCR management strategy throughout the soybean cultivation period.