A massive rat infestation is wreaking havoc on almond orchards across California’s San Joaquin Valley, with crop losses and infrastructure damage now estimated to exceed $300 million, according to a new report from the Almond Board of California.
Growers from Merced to Kern counties reported unprecedented destruction as roof rats chew through irrigation lines, strip bark from branches and feast on ripening nuts.
“We live in an infinite sea of rats,” Niamh Quinn, a University of California Cooperative Extension wildlife adviser, told the Fresno Bee. “They are everywhere.”
The almond board added that the rats are no longer confined to their traditional nests in trees. Many have turned to burrowing underground, particularly in orchards with limited winter ground cover — making them harder to detect and control.
Researchers believe irrigation canals and waterways are acting as thoroughfares, enabling rodents to spread rapidly between fields and outmaneuver containment efforts.
One farmer reported replacing an entire irrigation system for $20,000 after rats chewed through wiring and caused fires, according to the almond board. Another estimated a 50% crop loss, even while trapping up to 100 rats per day.
A 2024 survey by the California Department of Food and Agriculture found as many as 32 rats captured in a single night at some trapping locations.
Total economic losses for 2025 were projected at $109 million to $311 million, primarily from destroyed drip lines and reduced yields due to compromised irrigation.
Analysts noted these numbers probably underestimate the true impact, particularly on newly planted orchards.
Despite deploying bait stations, fumigants and owl boxes, farmers reported little success. Many said the efforts are costly, labor-intensive and inadequate given the scale of the outbreak.
“You are never going to kill all the rats,” Quinn said. “It will be a constant battle of monitoring and managing.”
Climate change may be compounding the crisis.
A study published this year in Science Advances found that rat populations grow faster in warmer conditions. Warmer conditions accelerate breeding cycles, allowing rats to reproduce more frequently and in larger litters.
The study documented sharp increases in rat complaints across 16 cities, including a 300% surge in San Francisco.
Researchers are urging growers to install surveillance cameras, elevate bait stations and conduct burrow fumigation to contain the spread.
Still, the Almond Board cautioned that without regulatory updates and more effective tools, the crisis is likely to escalate.
Industry leaders plan to address the growing threat at the upcoming CAPCA Conference in Reno and the Almond Conference in Sacramento, where new management strategies and policy recommendations will be on the agenda.
Source - https://www.sfchronicle.com
