The downy mildew disease of Impatiens found in the UK in 2003 for the first time was identified as being caused by Plasmopara obducens. This pathogen is reported to occur in North America and parts of Asia and Europe, including Denmark, Finland, the Netherlands and Germany in the EU and in the Czech Republic, Lithuania, Romania and Russia in the rest of the EPPO region. It may be more widespread. Its distribution has been described as worldwide (Anon., 2003). In 2003, the pathogen caused a significant disease of ornamental Impatiens, a valuable crop in the UK and this caused major concern to the UK bedding plant industry. In 2004 and 2007 several more outbreaks occurred in the UK but these have not been investigated. The pathogen is already present elsewhere in some EU countries and may be much more widespread than reported. It has been distributed to many locations in the UK. The full extent of its distribution in the UK is not known but it may also occur on natural relatives in the wild.