New sanitation rules allow harvest while protecting fields from broomrape
California’s processing tomato industry is taking major steps to prevent the spread of branched broomrape, a parasitic weed that damages crop by attaching to plant roots and draining nutrients. This marks the first time the industry has agreed to voluntary equipment cleaning and reporting guidelines aimed at limiting the weed spread.
Branched broomrape produces extremely small seeds that can remain inactive in soil for decades. These seeds can spread through wind, farm equipment, and even footwear. Since its return in Yolo County in 2017, the weed has raised concerns for an industry that generated $1.6 billion in 2024.
The University of California, Davis is playing a leading role by working with growers, regulators, and industry groups. Researchers are testing sanitation methods for harvesters and farm equipment, while also studying herbicides, detection tools, and other weed control methods.
“There’s 1,000 acres that are actually reported but we know from observation that it’s probably much greater than that,” said Cassandra Swett, a UC Davis plant pathologist who is leading efforts to sanitize field equipment.
“There are two main goals: reduce the economic impacts of broomrape on growers in the affected region by allowing them to harvest, and on the other side, keep broomrape out of the regions that do not currently have it,” said Swett.
Earlier state rules required entire fields to be destroyed if broomrape was found. Under new guidelines, growers may harvest their crops if they follow strict equipment cleaning standards developed by the California Broomrape Board, formed in 2024.
Most growers and processors joined compliance agreements in 2025, and mandatory rules are expected in 2026. Processing tomato canneries has also been committed to installing wash stations or following cleaning protocols.
“With the risk of crop quarantine off the table for growers under the compliance agreements, we can talk about the problem out in the open,” said Brad Hanson, a professor of Cooperative Extension in plant sciences and an ad hoc member of the Broomrape Control Board. “The daylighting part of this has been really helpful because for the last five years, we’ve been really in the dark.”
Cleaning farm equipment is challenging and time‑consuming, but new automated systems are being tested to reduce cleaning time without increasing risk. These efforts aim to balance weed control with harvest efficiency.
The new approach has encouraged openness among farmers, improving reporting, and helping the industry work together toward long‑term solutions that protect crops and future harvests.
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