Efficacy of Single- and Multi-Site Fungicides Against spp. of Strawberry.

Recently, the Florida strawberry industry faced unprecedented outbreaks of an emerging disease caused by the fungus spp. Currently, there are no fungicides labeled to control this disease in the United States and the efficacy of single- and multisite fungicides is unknown. Therefore, this study aimed to determine the in vitro sensitivity of spp. isolates to fungicides with different modes of action and to evaluate the efficacy of these products on detached fruit and in the field. In preliminary in vitro tests, 30 commercially available fungicides were screened using discriminatory doses. The effective concentration that inhibited mycelial growth by 50% was determined for the most effective single-site fungicides. Four field experiments were conducted during the 2019-20, 2020-21, and 2021-22 seasons to determine product efficacy in managing the disease. The single-site fungicides fludioxonil, fluazinam, and sterol demethylation inhibitors, and the multisite fungicides captan, thiram, and chlorothalonil were the most effective in inhibiting pathogen growth and suppressing disease development. Conversely, products in Fungicide Resistance Action Committee (FRAC) groups 1 (methyl benzimidazole carbamate) and 7 (succinate-dehydrogenase inhibitors), except for benzovindiflupyr, were not effective against spp. Resistance to fungicides from FRAC group 11 (e.g., azoxystrobin) was confirmed by the presence of the G143A mutation in the gene together with inoculation tests and field trials. Our results provide information to support or discourage the registration of fungicides to manage Neopestalotiopsis fruit rot and leaf spot in strawberry production.