Preventing the Spread of Plant Pathogens

SERCAL 2016 Technical Session, Tahoe

Chair: Carol Presley, Carol Presley Consulting

Lead presenters in alpha order

Over the past several years, numerous species of the pathogen Phytophthora (pronounced Fie-TOF-ther-uh) have been detected in California native plant nurseries and restoration sites. A species that had never been found in the US, Phytophthora tentaculata, occurred in several California native plant nurseries and was outplanted in restoration areas on sticky monkey flower (Diplacus aurantiacus), toyon (Heteromeles arbutifolia), coffeeberry (Frangula californica), mugwort (Artemesia douglasiana) and other native species produced as nursery stock. Preliminary follow-up investigations have identified more than 20 Phytophthora species in northern and southern CA native plant nurseries and restoration sites.  Several land owners have spent over $5 million to remove potentially infested plants from restoration areas, collaborating with scientists to develop and test new methods to eradicate these pathogens from contaminated soil. Phytophthoras are notorious plant pathogens, including the species that cause sudden oak death (Phytophthora ramorum), the Irish potato famine (P. infestans), and numerous diseases of agricultural, horticultural and forest plants. Inadvertently planting Phytophthora-infected nursery stock into native environs has the potential to introduce these pathogens into sensitive habitats. With the broad range of plants susceptible to Phytophthora, the pathogens can destroy the ecological values that restoration is trying to enhance. Efforts are underway to prevent pathogen introduction and spread by implementing Best Management Practices for native plant nurseries and restoration projects. Additionally, the Working Group for Phytophthoras in Native Plant Habitats is bringing all aspects of the problem together to coordinate a comprehensive, unified program of management, monitoring, research, education and policy to minimize the spread of Phytophthora pathogens. We need your ideas and observations about how to protect wildlands from these unintentional pathogen introductions into high-value habitats. 

Assembling a Response to Inadvertent Phytophthora Plant Pathogen Introductions in Restoration Areas: The Working Group on Phytophthoras in Native Plant Habitats

Susan J. Frankel*1, Janice Alexander2, Jessica Appel3, Diana Benner4, Elizabeth Bernhardt5, Cheryl Blomquist6, Tyler Bourret7, Matteo Garbelotto8, Janell M. Hillman9, Mia Ingolia3, Kathy Kosta6, Greg Lyman3, Heather Mehl7, Ellen Natesan3, David M. Rizzo7, Suzanne Rooney- Latham6, Alisa Shor10, Laura Lee Sims8, Karen Suslow11, and Ted Swiecki5

1USDA Forest Service, Pacific Southwest Research Station, Albany, CA, 94710; 2UC Cooperative Extension, Marin Co., Novato, CA 94947; 3Natural Resources and Lands Management Division, San Francisco Public Utilities Commission, San Francisco, CA, 94102;, 4Watershed Nursery, Richmond, CA 94804; 5Phytosphere Research, Vacaville, CA 95687; 6California Department of Food and Agriculture, Sacramento, CA 95832; 7Department of Plant Pathology, UC Davis, 95616; 8Department of Environmental Science, Policy and Management, UC Berkeley, 94720; 9Watershed Stewardship and Planning Division, Santa Clara Valley Water District, San Jose, CA 95118; 10Golden Gate National Parks Conservancy San Francisco, CA 94123; 11National Ornamentals Research Site at Dominican University of California, San Rafael, CA 94901;

Restoration projects serve as an inadvertent pathway for the introduction of invasive Phytophthora pathogens: preliminary surveys are detecting multiple Phytophthora species from restoration sites, purchased plants, and in native plant nurseries. The pathogens recovered pose a threat to native California flora; for example, Phytophthora tentaculata, new to the USA, is known to be present in seven California counties, on approximately 10 species of common California native plants, including sticky monkey flower (Diplacus aurantiacus = Mimulus aurantiacus), several Artemisia species, toyon (Heteromeles arbutifolia), coffeeberry (Frangula californica), and others. The “Working Group on Phytophthoras in Native Plant Habitats” is bringing together industry, scientists, regulators, native plant professionals, land managers, and others to prevent further introductions and spread by developing treatments, best management practices, and other changes to restoration practices. In this session, we will review 2014-2016 detections, pathogen distribution, threats, and progress on treatments for native plant Phytophthoras in California. A following discussion session will call on the audience for questions and ideas of how to protect wildlands from these unintentional pathogen introductions into high-value habitats.


Phytophthora tentaculata, a New Pathogen of Native Plants: The Story of a New Invasive Species Making its Way from the Nurseries into the Environment

Dr. Suzanne Rooney-Latham1, Kathleen Kosta*1, Karen Suslow1, and Kristina Weber1

1California Department of Food and Agriculture, 1220 N Street, Sacramento, CA 95814; 2National Ornamental Research Site at Dominican University of California (NORS-DUC), 50 Acacia Ave, San Rafael, CA;

In 2012, Phytophthora tentaculata, a pathogen known to cause root and crown rot of nursery plants in Europe and China, was detected for the first time in North America on declining sticky monkey flower plants (Diplacus aurantiacus) in a Monterey County native plant nursery. In 2014, the pathogen was again found, this time in toyon (Heteromeles arbutifolia) and Diplacus that had been planted at a restoration site in northern California. These plants were produced in a nursery in Placer County, where coffeeberry plants (Frangula californica) were also found to be infected. In response to these detections, the California Department of Food and Agriculture (CDFA) began trace-back activities to determine the distribution within the nursery and restoration systems. To date, P. tentaculata has been detected at nine nurseries in seven counties throughout California, and in four restoration areas in three counties. Awareness of the situation spread rapidly through the restoration and native plant nursery industries prompting widespread testing of nursery stock and outplanted materials. More than a thousand samples that have been collected from nurseries and wildlands were tested at the CDFA Plant Pest Diagnostic Laboratory by several diagnostic methods including DNA sequence analysis. In addition to P. tentaculata, more than 21 other species of Phytophthora were detected from the roots of symptomatic plants of many species of native plants. To date, P. tentaculata has not been detected in non-restored, wildland areas. In response, native plant nurseries are changing operations and implementing best management practices to insure clean stock production.


Preventing the Introduction of Invasive Soilborne Plant Pathogens into Restoration Planting Sites

Karen Suslow*1 and Kathy Kosta2

1Program Manager;National Ornamental Research Site at Dominican University of CA (NORS-DUC), Dominican University, Science Dept., 155 Palm Ave., San Rafael, CA 94901; 2Plant Pathologist; CA Dept of Food and Agriculture, 122 N Street, Sacramento, CA

Successful, sustainable restoration projects are the foundation of SERCAL. How do we educate the next generation of restoration practitioners to fully understand the repercussions of outplanting native plants infected with invasive plant pathogens into riparian areas and jeopardizing the integrity of the restoration environment? Root-rotting plant pathogens such as Phytophthoras exist worldwide. In 2012, a new plant pathogen, P. tentaculata, was discovered for the first time in North America in a CA watershed outplanting of native plants. In 2009, USDA Plant Epidemiology and Risk Analysis Laboratory published a list ranking P. tentaculata #5 risk threat of the 29 exotic species of Phytophthora not established in the contiguous United States. The list of prioritized Phytophthora species was generated using multiple criteria including knowledge of host range, geographic distribution, potential economic and environmental impacts, and potential pathways of plants imported into the United States. Within a short period of time, the pathogen has now been found in nine native plant nurseries in seven CA counties in northern and southern CA and in four habitat restoration sites. Over the past decade, the ornamental nursery industry, in conjunction with researchers and state and Federal regulators, have created a Best Management Practices document for growers which is being implemented in multiple states nationwide as part of a Systems Approach for managing pests and pathogens in the horticultural supply chain. Learn how and why many native plant nurseries are implementing a similar program to protect their plants and safeguard the native environment.

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