Santa Cruz County will test steam as an alternative to chemical soil fumigation on about 25 acres of Pajaro Valley farmland under a $175,000 state-funded pilot project set to begin this fall.
The California Department of Pesticide Regulation is funding the project, which will be led by the Santa Cruz County Agricultural Commissioner’s Office.
Agricultural Commissioner Dave Sanford said the county is working with about five growers, although participation is still being finalized.
At least two of the likely sites are near schools, including fields near McQuiddy Elementary School, and another ranch is near Holohan Road and the Pajaro Valley Unified School District offices. Sanford said selecting fields near schools and other sensitive sites was an intentional part of the project.
“That was sort of the goal of this as well, to highlight those sensitive sites and the ag-urban interface that we have in Watsonville,” Sanford said.
The on-the-ground steam treatments are expected to begin in September and could extend into early October, roughly the same period when conventional berry growers typically fumigate fields before planting.
Steam treatment involves injecting high-temperature steam into soil before crops are planted. The heat is intended to suppress soil-borne pathogens and could offer an alternative to chemical fumigants.
But Sanford cautioned that the technology is still being studied and is not ready to be considered a proven replacement for fumigation.
“There’s just a ton of work that has to be … done on this technology,” Sanford said. “It needs more investment, but it also needs trials like this” to demonstrate whether it is effective.
The project grew out of discussions between the Agricultural Commissioner’s Office and community groups seeking alternatives to fumigants near schools and other community-serving locations.
“The Pajaro Valley has some of the most concentrated use of fumigants in the state, including near schools and homes,” Kathleen Kilpatrick, a member of Safe Ag Safe Schools and a retired school nurse, said in a statement. “SASS members support exploring non-chemical alternatives on fields near schools. We hope these pilot projects will provide tools for pesticide reduction and expansion of organic buffers.”
SASS and the county Agricultural Commissioner’s Office brought the proposal to the Department of Pesticide Regulation for funding consideration.
Sanford said he had been participating in a working group studying steam technology and approached state pesticide regulators about funding a local sustainable pest-management pilot. DPR ultimately contributed roughly $175,000 award to include both research and community engagement.
The community component will include public outreach meetings and opportunities for residents to learn about the technology. Sanford said residents could potentially have opportunities to see the steam equipment operating in fields.
One of the questions researchers will examine is what happens to the soil itself when it is heated.
Sanford said newer steam equipment offers substantially greater temperature control than earlier versions, allowing operators to better target unwanted soil pathogens while limiting impacts on other parts of the soil microbiome.
Earlier steam systems lacked that precision. Sanford said older machines essentially heated sections of soil from above, sometimes overheating it.
Newer equipment uses shanks that can reach roughly 10 to 12 inches into the soil — about the depth used for conventional fumigant applications — and inject steam underground.
The tradeoffs are not limited to whether steam can control the same pathogens as fumigants.
Steam production requires substantial amounts of water, Sanford said, although he did not have estimates for how much water would be required per acre. Unlike conventional fumigation, however, the steam treatment itself does not use a chemical fumigant or pesticide.
Sanford said advances in equipment design could eventually make steam practical on a modest commercial scale, particularly in agricultural areas bordering neighborhoods, schools and other sensitive sites.
“These are hard spots,” Sanford said. “People aren’t too crazy about fumigants and pesticides and ag-urban interfaces. And if we can find some innovative technology that helps mitigate that, then I think it’s a win overall.”
The pilot comes as state regulators continue examining whether alternatives to chemical soil fumigants can work at a commercial scale.
The Department of Pesticide Regulation released findings in July from an independent state-funded study that concluded no existing alternative can currently serve as a direct replacement for chemical fumigants on a wide scale.
The study called for additional research into the soil and climate conditions under which alternatives could be effective.
The Santa Cruz County project will build on existing steam research. Sanford said UCSC researchers are leading the research component, and have previously studied steam treatments on farms in Monterey and Santa Cruz counties with support from a separate California Department of Food and Agriculture Biologically Integrated Farming Systems grant. Sanford described results from that earlier work as promising.
Researchers will take soil samples before the steam treatment and again about 30 to 40 days afterward. Additional measurements are planned in spring 2027, when researchers will also begin evaluating how berry crops perform in the treated areas.
That means the county will not have a definitive answer immediately after the steam equipment leaves the fields. Research is expected to continue into 2027.
The Agricultural Commissioner’s Office also plans to hold community meetings throughout the project for residents to ask questions and provide feedback.
The first meeting is scheduled for 5:30pm Aug. 18 in the Greg Caput Community Room at the South County Government Center, 500 Westridge Drive in Watsonville.
