In October 2012, nearly all the Diplacus aurantiacus plants grown in a Monterey County, California (USA) nursery for a restoration project were stunted and had dull and yellowish leaves. Roots and stem collars had necrotic, sunken lesions with few feeder roots. Approximately 30% of the plants had died. The causal pathogen was isolated and identified as Phytophthora tentaculata based on cultural, morphological, genetic (ITS) and pathogenicity analyses. This is thought to be the first report of P. tentaculata in North America.