Rats are infesting these nut trees in California and experts can’t explain why
California’s Central Valley is suffering from a rat problem, which is affecting a certain type of tree.
Across California’s Central Valley, almond growers are confronting an alarming surge of roof rats wreaking havoc across their orchards, a devastating phenomenon unlike anything the industry has seen before.
Stretching over 100,000 acres in counties like Fresno, Merced, Kings, and Kern, this rodent invasion is inflicting hugely costly damage, gnawing on expensive irrigation infrastructure, nesting underground, and stripping bark from trees, all while feasting on juicy almonds.
The losses are staggering. Estimates point to up to $310 million in damages, with replacements alone ranging between $56 million and $168 million. Perhaps most astonishing: some farmers are exterminating 50 to 100 rats per day, and in peak-affected areas, traps have captured as many as 32 rats per night.
Shaking almonds this week! DYK that California produces 80% of the world’s almond supply! pic.twitter.com/x3Ke2eoGnX
— Del Bosque Farms (@DelBosqueFarms) August 21, 2025
Rat infestation “the No. 1 issue I’ve dealt with”
“There are inquiries and questions about doing interviews on rat control and giving seminars on rat control, and can I write articles about this,’’ Rodent expert Roger Baldwin told USA Today. “The problem went from very, very low to being the No. 1 issue I’ve dealt with in my 17 years with UC.’’
As for why the rats are taking over, experts are baffled. Traditional tree-dwellers, these roof rats are now burrowing underground like guerrillas, making detection and control much more challenging.
However, there are several contributing factors that scientists speculate could be the reason behind the mess:
- Changing landscape: The end of California’s drought in winter 2022–23 brought wetter conditions, resulting in lush vegetation that supports rodent populations.
- Behavioural adaptations: These rats are exploiting irrigation canals and waterways as roadways to move swiftly between fields.
- Environmental shifts: Rising temperatures may be accelerating breeding cycles.
Farmers are deploying a range of preventive tools: bait stations, snap traps, owl boxes, and burrow fumigation using carbon monoxide or phosphide, but these are proving costly and are very labour-intensive.
Rats!
— Straight Arrow News (@StraightArrow__) August 19, 2025
California almond orchards, home to 80% of the world’s supply, are infested with rats, causing $110M–$310M in damage.
This hit on the industry comes as Trump’s retaliatory tariffs on China, which already cost almond growers hundreds of millions in lost business. pic.twitter.com/NGNBESJSxo
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As California supplies 80% of the world’s almonds, this crisis isn’t just local—it’s a global worry. “We’ve never seen anything like this,’’ Roger Isom, president and CEO of the Western Tree Nut Association, admitted to USA Today. “I’ve had growers who have lost more than half their yield. We’re not going to know until this year’s crop is in whether it was just weather-related or it was due to rat damage. It has certainly affected orchards. Hopefully, we can get ahead of this thing and prevent it from becoming a big, big issue.’’
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