SAN FRANCISCO – Rodent expert Roger Baldwin used to get less than one yearly inquiry about rat issues during most of his extended stint at the University of California-Davis, where he's a professor of cooperative extension focused on managing human-wildlife conflict. Now his phone keeps buzzing with dozens of requests from farmers, journalists and others seeking his expertise amid an unprecedented phenomenon: A massive assault by rats on the state's$4.7 billion almond industry. A newsletter this monthby the Almond Board of California said the infestation in parts of the San Joaquin Valley, one of the world's top agricultural regions, has impacted more than 100,000 acres and caused $109 million to $311 million in losses from damage to equipment and crops over a year. The sudden invasion starting last fall took growers by surprise, and they're still scrambling to figure out how to repel the intruders, often turning to Baldwin for guidance. "There are inquiries and questions about doing interviews on rat control and giving seminars on rat control, and can I write articles about this,'' Baldwin said. "The problem went from very, very low to being the No. 1 issue I've dealt with in my 17 years with UC.'' And it could have major implications if a solution is not found. California grows 100% of the nation's commercially produced almonds, the vast majority of them in the Central Valley, which comprises the San Joaquin Valley in the south and the Sacramento Valley in the north. The state accounts for more than 75% of the global almond production, exporting 70% of its output to100-plus countries. India is the leading customer. There's no clear-cut explanation for why rats on a large scale, which had been a bigger problem at citrus orchards, unexpectedly developed a taste for nut trees. But Baldwin and others in the know point to three contributing factors: ∎Well over half a million acresof California farmland were left unplanted in the early 2020s because of a protracted drought and diminishing water supplies, which also meant no pest-control efforts in those fields. ∎ The drought finally ended in the winter of 2022-23, the beginning of a three-year spell of at least average rainfall that resulted in more vegetation growth and an abundance of food sources for wildlife. ∎ State restrictions in the use of pesticides have limited the means growers have for getting rid of rodents. Those raiding the almond orchards also include squirrels, deer mice and others, though rats have been by far the most destructive. Baldwin said he has been told of some farmers who have spent hundreds and even thousands of dollars per acre on rat control over the last year. "At those levels, that's extreme,'' he said. "That's a very substantial cost.'' Much of the damage comes in the form of rats chewing on irrigation equipment such as drip lines, sprinklers and even electrical wires that activate water pumps, at times causing fires. In addition, the rats eat some of the almonds and "girdle'' or gnaw on bark, leaving the trees exposed and weakened. "Damage to irrigation systems, equipment and other infrastructure within orchards is often greater than direct crop loss,'' said the ABC newsletter, which gathered some of itsinformation from a surveyby the California Department of Food and Agriculture published in February. The almond board cited the example of one grower whose damaged drip-irrigation system cost $20,000 to replace, and another one with a crop loss of 50% because of the rats, despite exterminating 50-100 of them per day. The board said the rats have expanded their reach by traveling alongside waterways such as irrigation canals, and they have taken to burrowing under nut trees instead of nesting in them, making it harder to track and contain the rodents. They appear to spend the day in abandoned fields or vineyards that could still have some nuts and grapes, then make their way to the nut orchards at night, said Roger Isom, president and CEO of the Western Tree Nut Association, which represents growers and processors. He saw the remnants of one of their feasts last fall toward the end of the almond harvest, which typically runs fromAugust through mid-October. "Down in the base of a tree where it branches out, it was kind of like that was their dining table,'' he said. "You could see a bunch of empty shells where they were eating.'' Isom said Baldwin has been brought in to conduct seminars on comprehensive pest-management strategies, and the state has provided trainings for farmers to earn the certifications required to carry out fumigation in burrows. According to the almond board, other methods such as bait stations, snap traps and owl boxes – which draw the rodent predators – are also being employed, but farmers say the tactics are expensive and not entirely effective for a plague of this magnitude. The owl boxes have shown promise, Isom said, though it's too early to tell how much growers will be able to limit the damage to what's expected to become thesecond-largest almond harveston record. "We've never seen anything like this,'' Isom said of the rat incursion. "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.'' This article originally appeared on USA TODAY:Rats raid California almond orchards: 'Never seen anything like this'
