Phytophthora species are some of the most problematic plant pathogens in nursery production systems. The quarantine pathogen Phytophthora ramorum has received the most notoriety, but many Phytophthora species pose a challenge for nursery growers.
These pathogens cause trouble because of their persistence and spread in infested soil and water, and their ability to attack a wide variety of plants. Some species cause root rot, whereas others cause foliar blight and shoot dieback. Several species can infect plant parts both above and below the ground.
In collaboration with Niklaus Grünwald and Val Fieland of the USDA-ARS Horticultural Crops Research Laboratory, Carrie Lewis and I (Oregon State University) recently completed a three-year project to determine the most common sources of Phytophthora contamination in nurseries. We applied a systems approach to identify three critical control points in nursery production systems: contaminated soil/gravel beds, contaminated irrigation water, and used pots. Another potential source of Phytophthora spp., not included in our study, is nursery stock brought in from off site.