When the Marin County town of Fairfax had to suddenly close a local children's playground due to a flea infestation, city officials turned to Dominican University of California's National Ornamentals Research Site (NORS-DUC) for a solution.

The NORS team is using a nontoxic steam treatment to help battle the infestation, applying a protocol they developed more than a decade ago to combat the spread of sudden oak death from plant nurseries into the wild.

A collaboration between Dominican, the United States Department of Agriculture (USDA), and the California Department of Food and Agriculture (CDFA), the NORS-DUC research site studies emerging and invasive quarantine pathogens of ornamental and native plants in an open, nursery-like environment. The facility provides nursery growers with solutions, along with collaborating researchers with lab and field support, to aid in horticulture and plant disease management.

The key focus is on diseases caused by members of the genus Phytophthora, such as P. ramorum, the causal agent of sudden oak death and more recently P. tentaculata, a newly discovered plant pathogen in North America impacting native plant nurseries in California.

Laboratory studies conducted by the team found that heating soil to 122°F (50°C) for 30 minutes effectively kills the microorganism.

According to Dr. Wolfgang Schweigkofler, Research Professor and Director of NORS-DUC, the same heat-based approach can also control a variety of pests, including fleas.

"We have successfully treated areas infested by other pathogens and pests," Schweigkofler said. "Based on published research, both adult fleas and flea eggs can be killed at relatively moderate temperatures. Soil temperatures above 95°F are sufficient to kill flea larvae."

For the past several years, NORS-DUC has provided steam treatment services to nurseries and other clients throughout the San Francisco Bay Area and surrounding counties. The team brings its own equipment - including a SIOUX SF-20 steam generator and soil temperature sensors - and plans, conducts, and monitors each treatment.

"Steaming is a highly efficient and relatively fast way to combat both pests and plant diseases," Schweigkofler said. "It uses no chemicals, produces no toxic residues, and treated areas can be used again as soon as the process is complete."

Using its equipment, the team can treat soil plots measuring approximately 30 by 40 feet with a top-down steam application. NORS-DUC has also developed additional steam treatment methods for potting mixes, tools, and other agricultural materials.

The technology has been used in several other large-scale projects. In one case, the NORS-DUC team spent three days steam-treating more than 175,000 used strawberry containers at a Northern California farm. The treatment allowed the grower to safely reuse the plastic pots by eliminating traces of Phytophthora, reducing both costs and plastic waste.

Researchers have also tested heat treatment on wood infested with the Mediterranean Oak Borer, an invasive beetle that attacks mature oak trees in Northern California, particularly in Napa County and the Sacramento Valley.

In Fairfax, the steam treatment will rely on diesel-powered equipment to heat several hundred gallons of water, producing steam that will be released through hoses placed across the treatment area. The soil will be covered with tarps to retain heat, while temperature sensors monitor conditions below the surface.

Depending on the type of ground surface, each treatment area may take several hours to reach the target temperature. Once the coldest point reaches the required temperature, steam will continue for an additional 30 minutes before the site is allowed to cool. Afterward, the tarps, hoses, and sensors will be removed, leaving the soil moderately moist but free of chemical residues.

Because of the size of the playground, the Dominican team will complete two to three separate steam treatments over the course of two days.

_{Pictured: NORS-DUC's Vernon Huffman and the SIOUX SF-20 steam generator}

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