Suppression of White Rot of Welsh Onion by a Preplant Transplant Drench using Pyraziflumid

White rot caused by Sclerotium cepivorum, poses a significant threat to the production of Welsh onions. This study aimed to quantitatively assess the effectiveness and persistence of pyraziflumid when applied via preplant transplant drench. Six trials were conducted across five fields from 2020 to 2021. A day before planting, each paper pot tray was drenched with 500 ml of 2.2g/L of pyraziflumid. In the untreated Welsh onions, the disease was first observed in November in all trials. Subsequently, the disease incidence increased rapidly, and by January, nearly all plants were affected. Conversely, in the pyraziflumid-drenched trials, the disease was barely observed until January. The generalized linear mixed model analysis revealed that the estimated coefficient for pyraziflumid drench was −0.53 compared to no drench, significantly reducing disease incidence. The odds ratio was 0.005, indicating that pyraziflumid drench significantly reduced disease incidence compared to no treatment. The linear mixed model analysis showed that pyraziflumid drench significantly increased the yield of Welsh onion by 3.6kg/10a in plots infested with the disease. This despite, which requires only one time drench before planting, demonstrated excellent disease-suppressive effects and proved to be extremely labor-saving and economical.