| The emergence of Phytophthora ramorum in California has forced many changes in ornamental nursery management. Since P. ramorum is a quarantined pathogen, nursery managers are seeking better methods to keep the pathogen out of their plant stocks and more effective treatments to eradicate the pathogen if introduced. This research investigated the epidemiology of P. ramorum in California nurseries and developed options for management and eradication of this economically important plant pathogen.;A statewide survey identified 13 Phytophthora species in addition to P. ramorum that caused foliar symptoms on nursery plants. Phytophthora pseudosyringae and P. nemorosa, species thought to be strictly forest pathogens, were among those found. While P. ramorum was present in only eight percent of the foliar samples tested in 2005 and 2006, propagules of P. ramorum could be detected in soil and water samples in most of the infested nurseries. In vitro studies have identified chloropicrin, Telone C35RTM, BasamidRTM, VapamRTM, and iodomethane as effective fumigants for eliminating the pathogen from nursery beds. Heat ≥40°C also kills P. ramorum in soil within three days, while heating to 80°C can kill P. ramorum within 15 minutes. Soil treatments in several infested nurseries with Basamid or heat were successful in eliminating P. ramorum. In vitro studies also established that ≥0.2 mg/ml chlorine can kill P. ramorum in recycled irrigation water. Adding the cationic surfactants, benzalkonium chloride and cetyl trimethylammonium bromide, or ECCO Commercial All-Purpose cleaner, a surfactant made from plant extracts, also proved efficacious against P. ramorum propagules. On a volume basis, more surfactant is needed to completely kill propagules in pure water in comparison to chlorine; however, unlike chlorine, the efficacy of these surfactants is not compromised by high levels of organic residue which is a common factor in recycled nursery irrigation water. |
