Four-Year Field Evaluation of a New Thiocyanate Fungicide: Significant Reduction in Late Blight ( Phytophthora infestans ) Severity and Increased Potato Yield

Abstract

Abstract Late blight, caused by Phytophthora infestans (P. infestans), is a major potato disease worldwide. Resistance of P. infestans to existing fungicides necessitates alternative solutions with other modes of action. Previously, we reported a new family of fungicides: 2-thiocyano-1,3-dicarbonyl compounds, based on an in vitro study. Here, we present results of four-year field trials (2022–2025) evaluating the efficacy of the lead compound, 3-hexyl-3-thiocyanatopentane-2,4-dione, compared with fluazinam (Shirlan) for late blight control and yield improvement in the Moscow region (high P. infestans background). The experiment used a randomized block design (four replications) with the susceptible cultivar Red Scarlet. The thiocyanate fungicide consistently reduced the area under the disease progress curve by 27% (2022), 41% (2023), 66% (2024), and 72% (2025), compared with the nontreated control (NTC). Tuber yield increased by 10%, 66%, 85%, and 64%, respectively, vs NTC. Aqueous formulations of 3-hexyl-3-thiocyanatopentane-2,4-dione (119–200 g/ha) containing sodium dodecyl sulfate and sodium alginate showed the highest efficacy. These results demonstrate the potential of this new compound for effective late blight management and resistance mitigation strategies in potato production.