First report of Peronospora sparsa causing downy mildew on blackberry in Ohio.
In July 2017, symptoms characteristic of late-stage downy mildew were observed in a commercial blackberry (Rubus sp.) field in Wayne County, Ohio, USA. Disease incidence on cultivar Ouachita was 100% in two separate plantings. Symptoms included large (1 to 2 cm) brown to purple angular lesions on the upper surface of the leaves, leaf drop, and plant stunting. Sparse greyish white sporulation was observed in tufts within a lesion on the underside of the leaves. Based on morphological characteristics, sequence analysis of the rDNA internal transcribed spacer region and pathogenicity test, the causal agent was identified as P. sparsa. This fungus on blackberry has been reported in California and Arkansas. This is thought to be the first report on blackberry in Ohio.