More than 100,000 acres of almond orchards in Central California are infested

Almond growers across Central California say they are battling a surging rat infestation across more than 100,000 acres of orchards, resulting in economic hardship and damage.

Across Fresno, Merced, Kings and Kern counties, almond farmers have reported an increase in rodent populations as the rodents use irrigation canals and other waterways to spread across agricultural fields and orchards, according to a newsletter from the Almond Board of California.

The impact could be significant as California is home to 80% of the world’s almond production. The Golden State’s almonds were once the top export to China but retaliatory tariffs have resulted in China looking for almonds from other nations instead.

The newsletter doesn’t say what kind of impact the infestation could have on almond prices for consumers in California or the U.S.

Roof rats usually spend their lives above ground but have been burrowing under almond and other nut trees due to the absence of cover during the cold winter months, according to the newsletter.

A California Department of Food and Agriculture survey conducted during fall 2024 revealed that up to 32 rats were captured per night at some almond orchards, leading to tree damage from burrowing in the root zone, consuming nuts and disrupting the tree’s vascular system. Rodents also damage irrigation equipment and other infrastructure in the orchards.

Losses from rodents have ranged between $109 million to $311 million in California, according to the CDFA survey. Expenses include drip line replacements, which cost between $56 million and $168 million, and crop losses, which range between $43 million to $129 million. There were also costs associated with direct tree damage, farm equipment repairs, machinery cleaning and replacing damaged trees, according to the survey.

The CDFA report said the numbers could be underestimating the actual financial burden and that there could be more impacts, including to newly planted orchards and the cleanup after harvests.

The Almond Board of California reported that one almond grower had to replace their entire drip irrigation system for $20,000 and that the rats had caused fires by chewing through the irrigation wiring. Another grower also had 50% crop loss due to the extreme damage from the rodents. The grower reported having to exterminate between 50 and 100 rats per day.

Almond growers are using bait stations and aluminum phosphide treatments of burrows in the winter and, during non-winter months are turning to snap traps, owl boxes and fumigating the rats by applying carbon monoxide or carbon dioxide into burrows, according to the newsletter. These strategies can be labor-intensive, expensive and ineffective for large infestations.

Scientists have advised growers to use tracking tunnels, cameras and ink cards to monitor rat behavior in their orchards. They can then implement targeted baiting programs using oats treated with diphacinone — a slow-acting poison — and keep the bait stations full for about four weeks.

After the bait stations, snap traps can be placed in trapping tunnels for a long-term solution to the rat infestations, according to the newsletter.

The California Department of Fish and Wildlife is also warning trappers and hunters to keep an eye out for possibly contaminated wildlife in the area, and not to consume the tainted meat, over concerns the blue meat is a sign that the animal may have consumed poison meant for rats.