Rodents a Major Pain in California Orchards This Year

Rodents, particularly rats, have wreaked havoc in California orchards and vineyards this year, with some farmers reporting yield losses, damage to trees and destruction of irrigation lines, electrical wiring, and other infrastructure. Farmers face soaring costs not only to replace what has been destroyed or damaged but to control populations of the pests.

While the problem was initially reported in San Joaquin Valley nut orchards, Roger Baldwin, a wildlife specialist and expert in rodent management at the University of California, Davis, said it is more widespread. He noted he has also heard about rodent damage on the west side of the Sacramento Valley and along the Central Coast, particularly in citrus orchards.

“It seems to be a really bad rodent year in general throughout the state,” he says.

During a recent webinar on rodent management in agricultural settings, Baldwin said rats and voles have caused problems in certain parts of the state, and he’s received more calls than usual about ground squirrel damage.

“Rodent damage, if ignored, can lead to substantial losses,” he says. “I think this year is just a good example of how being a little bit more proactive may be beneficial in the long run.”

Chris Reardon, Director of governmental affairs for the California Farm Bureau, says the organization is monitoring the problem and has been working with county Farm Bureaus to help growers, including hosting the webinar and conducting a survey to assess rodent damage on farms.

Baldwin has studied different rodenticides for controlling roof rats in almond orchards, and says he found that using 0.005% diphacinone-treated oats inside elevated bait stations resulted in more than 90% reduction in rat activity.

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Got Voles Invading Your Nut Orchards? This Solution Goes for the Gut

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He recommends constructing the bait station using a 1 ½-foot-long PVC pipe with a 4-inch opening and caps on each end of the tube. Then drill about 1 ¾-inch holes toward the top portion of the bait station and place the station roughly 4 feet aboveground by attaching the tube to branches using bungee cords or zip ties. In his study, he placed his stations either 98 feet or 165 feet from each other throughout the orchard. Using 165-feet spacing reduces the cost, but efficacy drops to about 75%, he says.

“You want to try to minimize the number of stations you need while maximizing the effectiveness,” Baldwin adds. “The closer the stations are, the more likely it is that it’s going to work.”

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