Were the initial outplantings of P. ramorum-infested plants ever traced back to a source nursery?
Phytophthora ramorum was not discovered as the causal agent of sudden oak death until 2000-2001. Prior to then, it was not understood to be a nursery issue; therefore, there was no concern about spread from nurseries into the wildlands. Since then, DNA analysis has confirmed that the pathogen was unknowingly introduced to both California and southern Oregon via infected nursery stock from multiple nurseries. Prior to 2000 and our knowledge of the pathogen, it appears P. ramorum was moving around via the sale and trade of infected ornamental plants and possibly through movement of cuttings or rootstock for production. While we do not know where the pathogen originates from or how ornamental plant nurseries originally were introduced to it, we believe the nursery to wildland introduction in California began around 1987 in Marin and Santa Cruz Counties.