Understanding and Managing Sudden Oak Death in California

3.1.1. Nursery Stock

P. ramorum was originally introduced into California forests through movement of contaminated nursery stock. Federal and state regulations and inspections designed to prevent the movement of P. ramorum-infested nursery stock have been put in place. Nonetheless, contaminated nursery stock remains a pathway through which P. ramorum and other exotic Phytophthora species can be introduced to a site.

Nursery detections have been made in California and other states in every year since monitoring for P. ramorum was initiated. It is difficult to consistently detect nursery stock that is infested with P. ramorum, in large part,because:

Nursery grown plants that are most commonly infested with P. ramorum include species and varieties of camellia, rhododendron, pieris, and viburnum. These species in particular should not be planted adjacent to forests containing SOD-susceptible native species. Other species to avoid in such areas are those that are moderately to highly susceptible to P. ramorum and support moderate to high levels of sporulation (table 1-3).

Given the potential risks posed by P. ramorum and other pathogenic Phytophthora species, planting nursery stock in and near native forests should be avoided in general. Nursery-grown plants should not be used where spores produced on the plants could be dispersed into native stands or where contaminated soil or water runoff from the planted area can reach native stands.