In red crown rot (RCR) of soybean, the pathogen Calonectria ilicicola can infect soybean plants as early as 2 weeks after sowing. However, symptoms tend to manifest after the flowering stage. Various meteorological and agronomic factors have been thought to influence the progression from infection to symptom onset over several months. In order to clarify how these factors contribute to RCR incidence under field conditions, we analyzed the relationships between meteorological and agronomic variables and RCR incidence. Both agronomic and meteorological factors significantly influenced field-level incidence of RCR. High average temperatures exceeding 26°C and below 100 mm precipitation in August during the reproductive stage (R1–R5), as well as exceeding 200 mm precipitation in July during the vegetative stage, were associated with increased field-level incidence of RCR. Additionally, agronomic factors such as past RCR experience, the number of intertillage ridging applications, and sowing dates contributed to disease development. These findings were derived from a state-space Bayesian time-series analysis of RCR incidence across 242 fields in Akita, Fukushima, and Niigata Prefectures, Japan, from 2010 to 2012 and 2015 to 2018. The model incorporated precipitation and average temperatures in June, July, and August, along with previously identified agronomic variables. Although RCR is generally associated with high rainfall, our results suggest that high temperatures and low precipitation during the reproductive stage may also promote disease progression.
Ochi et al. (2026) studied this question.