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

Abstract

Recently, the Florida strawberry industry faced unprecedented outbreaks of an emerging disease caused by the fungus Neopestalotipsis spp. Currently, there are no fungicides labeled to control this disease in the U.S. and the efficacy of single- and multi-site fungicides is unknown. Therefore, this study aimed to determine the in vitro sensitivity of Neopestalotiopsis 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% (EC50) 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, the sterol de-methylation inhibitors (DMIs), and the multi-sites captan, thiram, and chlorothalonil were the most effective in inhibiting pathogen growth and suppressing disease development. Conversely, products in FRAC groups 1 (MBC) and 7 (SDHI), except for benzovindiflupyr, were not effective against Neopestalotiopsis spp. Resistance to fungicides from FRAC group 11, e.g., azoxystrobin, was confirmed by the presence of the G143A mutation in the cytochrome b 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.