Heat Check! Santa Cruz County Collaborative Tests Steam Injection as an Alternative to Traditional Soil Fumigation

Community members, growers and researchers team up for Pajaro Valley pilot project

On October 7, the Santa Cruz County Agricultural Commissioner (CAC) invited DPR, CalEPA, OEHHA, and local leaders to Watsonville to see how they are using steam to treat soil in berry fields, and hear from the community members, researchers, and growers who are making the project possible.

Steam treatment for pest management involves injecting high-temperature steam down into the topsoil before planting begins. The heat helps reduce or eliminate certain soil-borne pests, plant diseases, nematodes, and weed seeds.

Santa Cruz CAC David Sanford took interest in bringing the project to life after hearing about research being conducted at University of California, Santa Cruz (UCSC), where steam injection was being tested as an alternative to traditional soil fumigation on a limited scale. After learning more from UCSC researchers, Sanford saw an opportunity to bring industry and community together to explore steam’s effectiveness as a safe alternative to chemical fumigants.

“Using this innovative approach, we are testing to determine what’s feasible to try to support this as an alternative to traditional fumigation,” said Sanford.

Earlier this year, community leaders and Sanford’s office reached out to DPR seeking the department’s support to expand the UCSC project’s reach with a meaningful focus on community collaboration. DPR is funding the $175,000 pilot project. The money allows the CAC office to engage the local community, while continuing to work with researchers and berry growers in the Pajaro Valley to assess soil steaming as a potential non-chemical alternative to traditional fumigation. In turn, they opened the door to the public, holding forums to discuss the potential for steam as a safe alternative, especially near schools.

“Commissioner Sanford created an opportunity for the community to learn more about steam technology on a very comforting, one-on-one level,” said Yanely Martinez, the organizer of Safe Ag Safe Schools (SASS), “That was exactly what we needed.”

SASS is a coalition of 50-plus organizations and individuals working together to reduce pesticide exposure threats, especially near schools and child-care sites. For Martinez, a key strength of this project has been the conversations and outreach Commissioner Sanford has done throughout the area.

“The community has been partners in this effort and share our excitement for what this technology may bring,” Sanford said. “And growers are really looking for options, too. Right off the bat, they were both on board.”

The Case for Alternatives to Fumigation

One of the main goals of the project is to test the commercial effectiveness of steam injection as a potential alternative to chemical fumigation for preparing soils for planting berries, particularly near schools and residential neighborhoods.

In these locations, proximity to homes and schools means growers must navigate mitigation measures for protecting people’s health including buffer zone and timing restrictions that can make it challenging to chemically fumigate.

“The concerns of fumigants being used near schools is very real where we live,” said Omar Dieguez, an advocate from Watsonville who has been involved in the project through SASS.

Like other farming regions in the state, Santa Cruz County has experienced significant growth in recent years that has resulted in a challenging agricultural-urban interface. Some of the areas where people live, work, and play share proximity to farms, sparking worries among community members about pesticide exposure and conversations around needing safer alternatives.

“Steam as a potential alternative is a win-win that can both help growers while recognizing the needs of nearby communities,” said Sapna Thottathil, DPR Deputy Director of Sustainable Pest Management.

DPR’s 2024-2028 Strategic Plan outlines measures to advance access to safe, effective and sustainable pest management, emphasizing the importance of community needs and public input to accelerate the implementation of new pest management plans and tools. The plan sets specific goals for DPR to invest in projects that advance SPM practices and help establish partnerships like this one, where researchers, pest management practitioners, and community leaders are working together towards shared goals.

Can a Biologically Integrated System – with Steam as the Key Component – Help Reduce Fumigant Use?

The county is now working with multiple growers using steam across 25 acres of fields before blueberry, raspberry, and strawberry planting begins in the fall and spring seasons. The application involves injecting steam that is around 70 degrees into the ground for 20-30 minutes to eliminate pathogens, pests, and weed seeds.

UCSC is taking soil samples from test fields to compare results between steaming, fumigating, and from untreated control plots. Researchers will record soil samples at 7-day, 30-day, and 60-day intervals to measure soil pathogens and weed seeds, assessing the longevity of each treatment. They will look at disease incidents into spring and summer of next year in these fields to measure steam’s ability to eliminate plant disease.

“The use of steam to control pathogens and weeds has been around for 200 years,” said Dr. Jenny Broome, a plant pathologist who is leading UCSC research on the project.

Working with steam at such a large scale has been a challenge in the past. Broome has been working with steam since 2011. In 2024, UCSC received funding from the California Department of Food and Agriculture (CDFA) to research steam as a tool to reduce the use of fumigants. It was through this research that Commissioner Sanford and Broome connected.

Under the CDFA funding, Broome and other UCSC researchers conducted steam fumigation trials at two organic and two conventional farms. So far, the data that they’ve gathered is showing positive results.  “We are seeing really beneficial increases in yield and control of disease in all four farms compared to untreated controls,” Broome said.

The steam injection machinery being used for this project was developed by agricultural start-up High Degree, which also collaborated with UCSC on its previous field research. As the project moves forward, High Degree continues to refine their equipment in hopes of expanding what it can accomplish.

“We need to demonstrate that it works as well as fumigation, and we need to demonstrate that we can do it at scale in fields,” said High Degree CEO Austin Bowie. “That’s really what this project is all about for us; showing that steam injection can be a safe, effective alternative.”

Sustainable pest management is about finding and promoting alternatives to managing pests that can be economically viable, as well as environmentally and socially sustainable.

However, fumigant alternatives currently available have limitations. DPR commissioned a multi-part study exploring alternatives to fumigant pesticides, with results released between March 2025 and July 2026. The research conducted by the California Council on Science and Technology (CCST) followed the release of the Sustainable Pest Management (SPM) Roadmap to evaluate fumigant use and existing alternatives.

CCST’s independent research focused on evaluating possible alternatives to 1,3-dichloropropene (1,3-D) and chloropicrin, post-harvest commodity fumigation, and structural fumigation using sulfuryl fluoride. Their reporting indicates that while alternatives to these fumigants exist, there is no single alternative that can currently serve as a universal, one-to-one fumigant replacement.

“Our takeaway from this study is that more research and investment is needed in the space of alternatives, especially if we want to scale SPM statewide,” Thottathil said. “And this is where DPR can step in to kickstart and support innovation with projects and trials like this steam one.”

After speaking with others attending the steam demonstration, including CalEPA Secretary Yana Garcia, Dieguez believes collaboration is the key to solving pesticide-related issues in California.

“It’s very important, because these problems are not going to be solved by one agency, company, or person.”

To hear more from the project’s collaborators and see the steam injection equipment in action, visit DPR’s YouTube channel.

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