Screening and evaluation of smoke generators to control gray mold of Chinese chives

Effective and safe smoke generators were urgently needed to control gray mold of Chinese chives. In this study, the feasibility of processing nine commonly used fungicides into smoke generator was evaluated from five aspects: inhibition activity of active compounds, toxicity of smoke, smoke formation rate, safety, and field control. The inhibition activity of active compounds results showed that EC₅₀ values of fluazinam, fludioxonil, and pyrisoxazole against mycelial growth were 0.13, 0.05, and 0.12 mg/L; EC₅₀ values of pyrazolamide, fluopyram, and boscalid against conidial germination were 0.84, 0.68, and 1.16 mg/L. In a 0.108 m³ containment device, the toxicity of the smoke of fungicides at the same dose of 0.01 g was tested, the results showed that with the same dose of 0.01 g, the mycelial growth were completely inhibited by smoked fludioxonil, while the conidial germination was completely inhibited by smoked pyrazolamide, fluopyram, and boscalid, the inhibition rates of registered procymidone smoke generator against mycelial growth and conidial germination were 54.39% and 43.27%. The smoking rate of fludioxonil, boscalid, and fluopyram were 85.93%, 91.35%, and 82.86%, which conform to the criterion of active ingredient for fabricating smoke generators. Seven days after fungicide smokes treatment, there was no significant difference in plant height and stem diameter of Chinese chives compared with the untreated control. The results of the field trials in 2019 and 2020 showed that the curative efficacy of active ingredient of 120 g/hm² fludioxonil smoke generator to gray mold were 72.31% and 79.78%, and the curative efficacy of active ingredient of 375 g/hm² boscalid smoke generator to gray mold were 81.17% and 83.81%. Their curative efficacy was all higher than the procymidone smoke generator at the highest registered dose (the active ingredient of 450 g/hm²), in the treatment of grey mold of Chinese chives (59.86% and 63.71%). At the above doses, the preventative efficacies of three smoke generators to control gray mold were all above 90%. The dissipation dynamics of curves of the fludioxonil and boscalid were both in line with the first-order kinetic equation. The both half-lives of fludioxonil and boscalid in Chinese chives plant were 3-4 d. It is recommended that fludioxonil and boscalid are processed into smoke generators and registered for the prevention and control of gray mold of Chinese chives.