Tedmund J. Swiecki and Elizabeth A. Bernhardt, Phytosphere Research
Support provided by the Santa Clara Valley Water District, the California Native Plant Society, and Phytosphere Research
This website presents best management practices (BMPs) recommended for producing nursery container stock free of Phytophthora and other soilborne diseases. These BMPs provide an overall outline for producing container-grown plants free of Phytophthora species using a systems approach. They do not cover every practice or contingency that may arise in nursery plant production. A systems approach to clean plant production takes constraints and properties of the production system into account. Nursery growers are responsible for adopting practices that address additional risk factors (aka critical control points) that may exist in their nurseries.
Interest in BMPs was triggered by the widespread detection of multiple soilborne Phytophthora species in native plant nursery stock grown for habitat restoration projects and other uses. Phytophthora species are serious invasive pathogens that threaten California native plants in natural stands, restored habitats, and horticultural landscapes. Root rots caused by soilborne Phytophthora species have been recognized as important disease problems in nurseries for many decades. These plant pathogens can stunt or kill plants in the nursery, although infected plants may not show symptoms until nearly all roots are dead.
More importantly, infected nursery plants can deliver pathogens into the landscape. These introduced Phytophthora species can debilitate or kill the planted material, and spread from the planting site to attack and kill adjacent vegetation. The planting site can become permanently infested, causing long-term problems in the landscape, limiting the type of plants that can be grown, and serving as a source of spread to other areas.
A thorough, integrated systems approach to clean plant production is needed to produce plants that are free of Phytophthora. The concepts behind a clean production system can be summarized in two points
· Start clean by use of clean starting components, including plant propagules, containers, potting media, and water.
· Stay clean by using clean production practices and organizing your nursery in a way that separates potentially contaminated materials from your clean plants.
The goal of a clean production system is to prevent the introduction of Phytophthora into nursery stock rather than attempting to suppress it after plants are already infected. If there is no Phytophthora, there will be no Phytophthora diseases.