California imposes quarantine in Santa Clara County over medfly infestation
Through a press release, the California Department of Food and Agriculture (CDFA) informed that a portion of Santa Clara County has been placed under quarantine over a Mediterranean fruit fly or medfly infestation.
Local authorities implemented the measure after two wild female flies were detected in the city of San José. The CDFA is working collaboratively with the United States Department of Agriculture (USDA) and the Santa Clara County Division of Agriculture on this project, which is new and separate from the recently eradicated medfly infestation in Alameda County.
The quarantine area initially measured approximately 109 square miles and covered parts of the cities of San José, Santa Clara, Campbell, and the town of Los Gatos. A few days later, the CDFA announced it extended the quarantine area to include parts of the city of Milpitas—you can use the agency's interactive map to get an up-to-date view of the region impacted by this initiative.
The measure will affect any growers, wholesalers, and retailers of susceptible fruit in the area, as well as local residents. Home gardeners are urged not to move homegrown produce from their property.
The science behind eradicating a medfly infestation
To get rid of the pest, authorities will release sterile male medflies in the area at a rate of 250,000 specimens per square mile per week in an 84.76 square mile area around the infestation. Sterile male flies mate with fertile wild female flies in the natural environment but produce no offspring. The fly population decreases as the wild flies reach the end of their natural life span with no offspring to replace them, ultimately resulting in the eradication of the pest. This program has a proven track record of eradication in California.
Additionally, properties within 200 meters of the detection sites are treated with an organic formulation of Spinosad. This compound originates from naturally occurring bacteria in soil and is used to eliminate mated females and reduce the population density. To further reduce the population, properties within 100 meters of infested properties are subject to host-plant or fruit removal to eliminate eggs and larvae.
This eradication approach is the standard medfly program used by CDFA and is the safest, most effective, and most efficient response program available. CDFA has successfully eradicated every detected medfly infestation in California history, dating back more than 40 years.
UPDATE | August 29, 2025, at 08:02 EST—This story was updated to reflect the CDFA's extension of the quarantine area announced on August 28.
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