Baseline sensitivity and control efficacy of fluazinam against Clarireedia homoeocarpa

Abstract Clarireedia homoeocarpa (formerly called Sclerotinia homoeocarpa) causes dollar spot, one of the most important diseases of turfgrasses worldwide. The dinitroaniline fungicide fluazinam was recently registered for turfgrass. In this study, baseline sensitivity, toxicity and control efficacy of fluazinam against C. homoeocarpa were investigated. The frequency of sensitivities had a unimodal distribution (Kolmogorov-Smirnov, P = 0.20). The mean EC50 value was 0.0226 ± 0.0109 μg ml−1 with individual values ranging from 0.0032 to 0.0440. Fluazinam increased the number of hyphal offshoots, cell membrane permeability, and inhibited oxalic acid production. No positive cross-resistance between fluazinam and thiophanate-methyl, propiconazole, or boscalid was observed. Fluazinam at 1 μg ml−1 can reach 90.10% preventative control efficacy on detached leaves; while, the curative control efficacy of fluazinam at 5 μg ml−1 was less than 60%. The preventative control efficacy of fluazinam in the field was consistently more than 97% in 2017 and 2018. The curative control efficacy in the field reached 75.56% in 2017 and 95.91% in 2018. Both preventative and curative control efficacies of fluazinam were better than propiconazole and fludioxinil over two years. The results have important implications for managing dollar spot disease and fungicide resistance problems in C. homoeocarpa.