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Abstract
This illustrated guide provides background information and guidance to help resource management professionals and land managers identify habitat restoration sites that have been affected by introduced root-rotting
Phytophthora species. Restoration sites have become persistently infested with soilborne
Phytophthora species by the planting of nursery stock with Phytophthora root rot. These infestations can spread beyond planted material into adjoining native vegetation, resulting in expanding areas of plant decline and mortality. Root-rotting
Phytophthora species decay fine roots and may cause basal stem cankers. This damage induces shoot symptoms related to acute or chronic water stress in infected plants. Because many other agents and environmental conditions can induce similar or identical shoot symptoms, diagnosis of Phytophthora root rot requires sampling and testing to detect
Phytophthora in the root systems of affected plants. We provide guidance for sampling plants to detect soilborne
Phytophthora by baiting of root/soil samples. Topics include strategies to optimize detection and minimize false negative results; details of sample collection, including timing, plant selection, collection and handling; and phytosanitary practices to prevent spread of contamination. We describe specific methods for baiting samples with green (unripe) pears to detect
Phytophthora. Identification of
Phytophthora infestations in restoration areas can inform management to prevent further pathogen spread within and beyond infested sites.
Citation
Swiecki, Tedmund J.; Bernhardt, Elizabeth A.; Bourret, Tyler B.; Frankel, Susan J. 2025. Sampling to detect soilborne
Phytophthora infestations in California habitat restoration plantings: a technical guide. Gen. Tech. Rep. PSW-GTR-279. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 63 p. https://doi.org/10.2737/psw-gtr-279.
