Native-plant nurseries seek to combat Phytophthora

Upgrades can nearly double expenses

At Foothills Park in Palo Alto, the Grassroots Ecology Nursery has taken on a hospital-like ambiance. No one sets foot in the nursery without first dipping the bottoms of their shoes in an isopropyl alcohol bath, and they must follow the same procedure whenever entering any of the greenhouses, where all surfaces, from tables to walls, are steam sterilized, and all tools are cleaned with alcohol.

The grounds and each "cleanhouse" are covered with barrier cloth, and the cleanhouses also sit on a bed of gravel about four to six inches thick. Inside, the benches are all made of plastic or metal and must be three feet above ground -- the "splash zone" for dripping water. Every tray of nascent seedlings uses potting soil pasteurized on site in a soil kiln and no pots are reused. No container sits on the ground. There are layers of checklists for taking plant cuttings and identifying healthy plants, and each step of every process is carefully recorded, nursery manager Nikki Hanson said.

The setup follows new protocols to help prevent the spread of Phytophthora, the root-rotting water molds that have found their way into many nurseries around California and in other states. Phytophthora causes diseases such as root rot, stem cankers, and leaf and fruit blights. Some species can infect hundreds of plant species, according to Ted Swiecki and Elizabeth Bernhardt of Phytosphere Research.

In a February 2016 study, Swiecki and Bernhardt found that plant nurseries are ripe for soil-born Phytophthoras, having wet, humid conditions and high root density in containers, and using fungicides that suppress the disease but don't kill it.

A 2015 report by the California-based Working Group on Phytophthoras in Native Plant Habitats found of 20 nurseries that submitted samples between January and June 2015 to the California Department of Food and Agriculture laboratory for testing, 15 nurseries, or 75 percent, had at least one Phytophthora species detected.

Grassroots Ecology Nursery is one of a handful of native-plant nurseries, large and small, currently working with researchers and land managers to identify "best management practices" to prevent spread of the disease. The nursery, a nonprofit, has been able to fund its upgrades through grants and partnerships with public agencies. Midpeninsula Regional Open Space District and Santa Clara Valley Water District both have dedicated greenhouses at the nursery.

But the effort has not come cheaply. The nursery's costs have increased by 40 to 50 percent, Executive Director Alex Von Feldt said. That translates into increased costs for nursery stock. But land managers such as Cindy Roessler, senior resource management specialist at Midpeninsula Regional Open Space District, said they are willing to pay for clean plants.

Roessler said that while protocols are in the development stage, there is much debate among nurseries about how to balance cleanliness with practicality. No one wants to make the rules so stringent that they are unachievable or put the nurseries out of business. For large nurseries and some smaller ones, the reality is the costs might prove prohibitive.

Swiecki and Bernhardt said that ideally ornamental nurseries, which import many plants, would also adopt similar practices to curb the introduction of existing and new Phytophthora species from overseas. One of the largest outbreaks of Phytophthora pathogens, Phytophthora ramorum, spread from chrysanthemum and rhododendrons and is now prevalent in wildlands, killing millions of oaks in California.

Read the cover story, "Deadly disease plagues plants high above Silicon Valley"


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