Performance of two- and three-way fungicide premixes for the control of soybean target spot after seven years of use

Target spot, caused by Corynespora cassiicola, is an economically important disease of soybean, especially in Brazil. The performance of two commonly used fungicide premixes: a two-way (fluxapyroxad + pyraclostrobin) and a three-way (bixafen + prothioconazole + trifloxystrobin) premix for the control of target spot, have been tested over seven growing seasons (2016/2017 to 2022/2023) across six Brazilian states (MT, MS, DF, GO, TO, and PR). A network meta-analysis model was fitted to disease severity and yield data from 22 trials, and expanded to include harvest year as a continuous moderator. The overall disease control efficacy was higher (61.3%) for the three-way than for the two-way premix (44.6%). For yield, the three-way premix led to a higher yield return relative to the untreated control (+ 647 kg/ha) than the two-way premix (+ 414 kg/ha). Year as moderator variable in the model helped to explain a portion of the variance of the two variables. A decline of 5.9 percentage point/year in disease control efficacy was found for the two-way premix and a decline of 1.8 percentage points/year for the three-way premix. The reported decreasing efficacy of the fungicides over time is in agreement with reports of resistance in the population of the pathogen.