First report of powdery mildew (Sawadaea bicornis) on bigtooth maple (Acer grandidentatum) in the U.S.A.
During the 2017 autumn and 2019 spring seasons, powdery mildew was found on bigtooth maple (Acer grandidentatum) trees in northern Utah, USA. It was present in hedges in Logan, Utah (1350 m elevation), with 100% of the plants affected as well as in the mountains (2100 m elevation), with 10% of the plants affected. The powdery mildew infected and colonized newly emerged leaves, covering both leaf surfaces with white mycelium. Chasmothecia were found on some leaves and scattered across the adaxial leaf surface. The causal pathogen was isolated and identified as Sawadaea bicornis based on morphological, molecular and pathogenicity analyses. This is thought to be the first report of S. bicornis on bigtooth maple in the USA.