Phytophthora tentaculata is a plant pathogen that causes root and stalk rot. It was first isolated in Germany and was thought to be restricted to Europe, but it was found in a Monterey County nursery in 2012 (http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-09-13-1002-PDN) and has since been found in nursery stock in Alameda, Butte, Placer and Santa Cruz Counties and in nursery stock that had been planted at restoration sites in Alameda County. The USDA Forest Service, Pacific Southwest Research Station, Forest Health Protection, California Department of Food and Agriculture and Phytosphere Research are cooperating to inspect restoration sites to determine the extent of introduced infestations.
The affected plants in California include sticky monkey flower (Mimulus auranticus), California coffee berry (Frangula californica), toyon (Heteromeles arbutifolia) and various Salvia species.
Host species include: Chrysanthemum species, Delphinium ajacis (Rocket larkspur), Verbena sepcies, Gerbera jamesonii (Gerbera daisy), Origanum vulgare (oregano), Santolina chamaecyparissus, Lavendula angustifolia (English lavender), Chichorium intybus (common chicory), Auklandia lappa, and Calendula arvensis (field marigold).
The symptoms include root and stem rot, with the roots and stem collars developing necrotic and sunken lesions with fewer feeder roots. Above ground symptoms include stunting, leaf russeting, yellowing to browning foliage, leaf drop and dieback of twigs, brown to black lesions girdling the basal stem, and eventual death of the plant. The spreading mechanism was not discussed in the article.
We are entering planting season for native plants, and the infested nurseries specialize in growing native plants for restoration work. This makes the odds of unintentionally introducing the disease into the wilderness very high. Please think twice and inspect carefully before choosing to use nursery plants in your projects.
Information from “Between the Furrows, October 2014