Baseline sensitivity and efficacy of the sterol biosynthesis inhibitor triflumizole against Botrytis cinerea

Triflumizole is a broad-spectrum fungicide in the chemical group of imidazoles. In the present study, the biological activity of triflumizole on Botrytis cinerea was determined in vitro, and the protective and curative activity against the fungal pathogen was determined on cucumber true leaves. Moreover, the baseline sensitivity for mycelial growth of B. cinerea to triflumizole was determined in vitro with a set of 79 isolates obtained from different geographical regions in Shandong Province of China. Inhibition of mycelial growth was found to be the most sensitive growth stage affected by triflumizole, whereas spore germination of B. cinerea was the least sensitive growth stage. Triflumizole provided excellent curative activity against B. cinerea at concentrations of 100 and 200 μg mL−1 and also was highly protective against the fungus at 200 μg mL−1. However, the control efficacy of protective activity and curative activity were relatively low when the concentration decreased to 50 μg mL−1. The baseline sensitivities were distributed as a unimodal curve, with a mean EC50 value of 0.58 μg mL−1. The individual EC50 values for triflumizole ranged from 0.15 to 1.49 μg mL−1. Triflumizole had no cross-resistance with other botryticides, including carbendazim, iprodione, diethofencarb, pyrimethanil and boscalid. However, cross-resistance to SPY-Z048, which is also a sterol biosynthesis inhibitor, was observed. In field trials in 2014 and 2015, triflumizole used at a concentration of 150 g a.i. ha−1 provided control efficacy on leaf ranging from 80.76 to 86.32 %, and its control efficacy on fruit could reach 84.93 % ~89.06 %, which were higher than the control efficacy of other treatments. These results suggested that triflumizole will be a good alternative fungicide for control of grey mould.