First report of downy mildw caused by Plasmopara halstedii on black-eyed Susan (Rudbeckia fulgida cv. 'Goldsturm') in Maryland.
In September 2013, disease symptoms characteristic of downy mildew were observed from multiple black-eyed Susan (Rudbeckia fulgida) plants at 2 commercial nurseries in the counties of Howard and Anne Arundel in Maryland, USA. Over 100 R. fulgida were affected by this disease in both nurseries, rendering the plants unmarketable and causing a substantial financial loss. Plants exhibited dark necrotic lesions on the adaxial leaf surface and sporulating masses of white mycelium on the abaxial leaf surface and on the adaxial in extreme infections. Plants were stunted with a reduced number of blooms. The causal pathogen was identified as Plasmopara halstedii based on morphological, genetic (BLAST and PCR) and pathogenicity analyses. This is thought to be the first report of P. halstedii on R. fulgida cv. Goldsturm in Maryland.