Evaluation of oxathiapiprolin for the management of grapevine Downy mildew

Downy mildew is a yield-limiting disease of grapevine, caused by the pathogen Plasmopara viticola. Oxathiapiprolin, the first member of the piperidinyl thiazole isoxazoline fungicides, was evaluated for efficacy on downy mildew in a field trial conducted in 2021 at the Research and Development Institute for Viticulture and Oenology Valea Calugareasca. Throughout the study, the rate range was narrowed from active ingredient (a.i.) at 200+1600 to 85+85 g a.i. to an optimal effective rate of 20+1000 g a.i./ha. Within that optimal range, the downy mildew incidence treated with oxathiapiprolin and competitive commercially available fungicides was significantly lower than the incidence in the nontreated grapevine with disease pressure. There were no significant differences in the efficacies of product Zorvec (oxathiapiprolin+folpet, co pack) (97,7-98,6%) and the standard fungicide Profiler (fluopicolide+fosetyl-aluminum), (96.9-97.8%). To avoid the development of resistant strains and at the same time to enhance efficacy, in the field, with favorable weather conditions for pathogen growth, two resistance management practices were considered: (I) a preventive foliar application, forecast (to determine the spray timing), with use the fungicides, typically used in IPM, only in tank mixtures or pre-packs; (II) an eradicative foliar application of the systemic fungicides with the purpose off cure existing infections.