Native Plant Group Supports Clean Nursery Practices

Press Release
Contact: Dan Gluesenkamp,
Phone 916- 447-2677
2707 K Street, suite 1
Sacramento, CA, 95816

Native Plant Group Supports Clean Nursery Practices

Our California landscapes are facing threats from new diseases that we are not prepared to control once they are introduced.  The greatest threat is from exotic plant pathogens called Phytophthora pronounced Fie‐TOF‐ther‐uh), which is the Latin term for “plant destroyer,” and includes the sudden oak death pathogen that has killed over 3 million oaks in California since its introduction on nursery stock some 30 years ago.

In San Carlos last December, the California Native Plant Society (CNPS) adopted a policy to provide leadership on this threat to native plants and their habitats. “This policy supports plant nursery and propagation practices that help prevent plant diseases and that discourage the spread of Phytophthora and other harmful plant pathogens in California” said Dan Gluesenkamp, Executive Director of CNPS.  “CNPS will educate native plant nurseries and give special attention to stock propagated or sold by our local chapters.”

What is Phytophthora and How Can it Spread?

Phytophthora is a genus of microscopic water molds, fungal‐like organisms.  Most if not all of the over 120 described species cause plant diseases, including many of the most serious plant diseases worldwide.  Increased international trade in live plants, especially nursery plants, has increased the rate at which these exotic pathogens are introduced to new areas.  Many native plant species have little or no resistance to these invasive pathogens and may be killed or severely weakened when infected.

During the past several years, a first‐in‐the‐USA detection of Phytophthora tentaculata occurred in several California native plant nurseries and in Bay Area habitat restoration site on outplanted nursery stock. 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.

“In addition to coast live oak, native species of manzanita, madrone and bay have been recognized as dying from Phytophthora infestations that have been introduced into their habitats” according to Gluesenkamp.  “Now the native plants popular for landscaping, bush monkey flower (Diplacus aurantiacus), sage (Salvia sp.), coffeeberry (Frangula californica) and toyon (Heteromeles arbutifolia) have been found to be hosts of these harmful pathogens.  Planting of Phytophthora‐infected nursery stock plants can inadvertently increase these pathogens into home landscapes and native habitats.”

“We are working from an abundance of caution developed from experience with the sudden oak death pathogen”, said Ted Swiecki, a plant pathologist who has studied Phytophthora for many years and is advising CNPS on implementation of its policy on plant pathogens.  “Once these pathogens become
widely established in native habitats, they are impossible to eradicate.”

Plant Pathogen Concerns Grow Among CNPS Chapters

Interest in plant pathogens grew within CNPS following a pest alert released in February 2014 from the U.S. Department of Food and Agriculture on the discovery of P. tentaculata in California.  “The following December we helped organize a seminar at the Presidio in San Francisco for the California Native Nursery Network to educate nurseries on Phytophthora species, how they affect native plants, and how they spread in nurseries and wildlands” said Swiecki.  In January 2015, CNPS organized a statewide conference on conservation of California native flora in San Jose to help mark the 50th anniversary of its
founding that included sessions on Phytophthora and other pathogens and pests found in California landscapes.

Local chapters became more educated on Phytophthoras and at the quarterly meeting of CNPS Chapters in Quincy last May, they established an ad hoc group to identify a role for CNPS in preventing in the infection and further spread of these harmful plant pathogens.  This ad hoc group drew from scientists,
botanists, plant pathologists, public agencies and nurserymen throughout the state and immediately began work on a policy to guide CNPS leadership.

CNPS works closely on habitat restoration projects in California, and local chapters use native plant sales to raise funds for their local conservation efforts, so the ad hoc group drafted a policy to promote healthy nursery stock for habitat restoration sites and CNPS‐sponsored native plant sales.  “Producing healthy nursery stock that is safe to plant requires practices similar to producing food that is safe to eat” said Swiecki.  “Soil, containers, equipment, plant material, and water must be free of pathogens and contact with possible sources of contamination, such as the ground, needs to be avoided.”

Plant Pathogen Policy can Increase the Cost of Native Plants

The ad hoc group worried that some recommendations will increase the cost of native plant nursery stock, said Gluesenkamp.  “But their discussions always came back to the fact that many nursery practices were threatening native plants in natural stands, restored habitats, and residential landscaping.  As the principal organization dedicated to California’s native flora, we should do no harm if nothing else.”

Gluesenkamp says “the policy will be used to guide our conservation activities with the nursery industry and government agencies to ensure that habitat restoration projects use biologically clean and healthy nursery stock, and will provide support to local chapters to reduce their risk of selling infected plants at
their native plant sale fundraisers. It is encouraging that many nurseries are helping develop best
management practices for nursery operations.  Our aim is to work together.”

Plant pathologist Dr. Elizabeth Bernhardt collects data in a stand of endangered Ione manzanita
(Arctostaphylos myrtifolia) and whiteleaf manzanita (A. viscida) decimated by the introduced soilborne
pathogen Phytophthora cinnamomi (Photo: Ted Swiecki, Phytosphere Research).

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