The presumably North American species Plasmopara wilsonii is present in Germany on the ornamental plant Geranium phaeum

Geranium phaeum is a popular ornamental plant in Europe. Downy mildew disease caused by Plasmopara was found on this plant once 50 years ago in Poland, but at that time attributed to the native species, Plasmopara pusilla. Here we report the recurrence of downy mildew disease on G. phaeum in Germany. Molecular phylogenetic analysis and morphological investigations revealed that the causal agent of the new outbreak is P. wilsonii, but not P. pusilla. Plasmopara wilsonii had previously been found only in the USA and Korea on various hosts of Geranium. The presence of P. wilsonii on G. phaeum in Europe should be closely monitored, as downy mildew caused by this species probably has the potential to become an important emerging disease on its ornamental host, especially, as also the native G. molle is able to sustain the pathogen.