Poor Control of Cucurbit Powdery Mildew Associated with First Detection of Resistance to Cyflufenamid in the Causal Agent, Podosphaera xanthii, in the United States

Abstract

This report is about the first known occurrence of resistance to cyflufenamid, a Fungicide Resistance Action Committee (FRAC) code U6 fungicide, in Podosphaera xanthii in the United States. This fungus causes powdery mildew in cucurbit crops, the most common disease of this important crop group. Knowledge about resistance is important for guiding fungicide programs. Mobile, targeted fungicides, which have moderate or high resistance risk, are the most effective management tool for this disease. The pathogen is a documented high resistance risk organism having already developed resistance to fungicides in FRAC groups 1, 3, 7, 11, and 13.