Many of the plants that are grown in the PNW forest and native plant nurseries are hosts for P. ramorum. In addition to the economic impact that nurseries would suffer if P. ramorum was to be detected, the movement of infected plant material from these nurseries would likely result in the introduction of the pathogen into forest or natural sites. This may have significant economic and/or ecological impacts.
There are a number of phytosanitary measures that native plant nurseries can take to minimize the risk of inadvertently introducing P. ramorum or other Phytophthoras into a nursery site. Given the continued spread of P. ramorum inoculum from ornamental nurseries into nearby waterways, one of the keys is to treat any water that is used from streams or lakes for irrigation.
Another key is to be very careful about the plant material that is brought into the nursery and inspect new shipments closely for symptoms, especially if they are coming from an area where P. ramorum is established.
Native plants used in restoration sites are at risk for spreading P. ramorum into forests if they are infected. It is important to be aware of the source of irrigation water for these plantings.
Phytophthora and other diseases can spread in residual soil and plant material in pots that are re-used. Pots can be treated with disinfectants or heat to kill these organisms.
California Society for Ecological Restoration Quarterly Newsletter Summer Volume 26, Issue 2 has these two articles:
“Nursery Plants as a Pathway for Plant Pathogen Invasion” by Susan J. Frankel, Kathy Kosta, and Karen Suslow
“Solarization: A Simple and Low-Cost Method for Disinfesting Horticultural Containers” by Karen Suslow and Kathy Kosta
A Phytophthora tentaculata Pest Alert is now available. P. tentaculata is an emerging pathogen in California native plant nurseries and restoration plantings.
So far, P. ramorum has not escaped into the natural environment in the PNW except for in streams associated with positive nurseries and landscapes. Research on the amount of inoculum needed in water for infection, susceptibility and sporulation potential of plant hosts, and other topics will help us determine the level of risk to our forests. In the meantime, it pays to be cautious when working with host plants.
Photos of native plant nursery best (and worst) management practices
If you have ideas or photos to add to these pages, let Marianne know.
Thanks to Regina Johnson for many of the photos used in this section.