A Decade of European Monitoring Studies on Fluopicolide Sensitivity of Phytophthora infestans and Greenhouse Efficacy of Commercial Products to Control Potato Late Blight

Abstract Phytophthora infestans is a hemibiotrophic oomycete pathogen that causes late blight in important Solanaceae crops worldwide, including potato producing countries. The pathogen can infect leaves, stems, and tubers of potato plants, leading to substantial yield losses during cultivation and storage. To prevent local infections leading to widespread epidemics, oomyceticides are widely used. In 2006, fluopicolide, an inhibitor of the vacuolar H + -ATPase, was registered in Europe and introduced to the potato market together with propamocarb hydrochloride in the mixture product Infinito®. In this study, fluopicolide sensitivity data for 460 P. infestans isolates were summarized for the years 2013 to 2023, originating from different countries in Northern, Central, and Southern Europe. For fluopicolide, field resistant strains have not been observed until now in European late blight monitoring programs. In addition, greenhouse trials were testing the efficacy of the mixture product Infinito® against the dominant sub-populations of P. infestans of the last decade: EU_13_A2, EU_33_A2, EU_36_A2, EU_37_A2, EU_41_A2, EU_43_A1, and EU_46_A1. All experiments showed a high efficacy of Infinito® (70 to 99%) comparable or better than the market standard fluazinam (Shirlan®, 0 to 97%). These results highlight the reliable efficacy of fluopicolide-based products to control P. infestans , independent of the European sub-population. Therefore, the proactive resistance management strategies implemented were able to prevent the occurrence of fluopicolide-resistant strains of P. infestans in Europe.