Making a salad is getting more expensive. Is climate change to blame?

In his nearly four decades of growing lettuce, spinach, kale and other leafy greens in California and Arizona, Tony Alameda has seen plenty of bad years. But lately, he said, there have been many more “noticeably bad” years in a row.

“2022 is probably the worst we’ve seen,” said Alameda, vice president of Topflavor farms, a family operation he runs with his brothers. In October and November, dual outbreaks of a soil-borne disease and an insect-transmitted virus ravaged the Salinas Valley in California and caused thousands of acres of lettuce crops to wilt.

Now, winter growing schedules and changing weather patterns mean the bad luck has migrated from the Central Coast valley that served as the backdrop for John Steinbeck’s “Of Mice and Men” and other novels to the desert farming regions near the U.S.-Mexico border.

“We’re going from one problem in the north to one problem in the south,” Alameda said. “They’re completely separate problems, but they end up combining to really make a long period of shortage of vegetables.”

As a result, consumers across the country are seeing stark price increases in lettuce, with the cost of a carton of iceberg lettuce skyrocketing from about $20 last December to more than $105 earlier this month, according to data from the United States Department of Agriculture. The Mercury News reported some sellers charging nearly $11 for a single head of lettuce.

Experts say bad luck alone may not be to blame, however. The virus, impatiens necrotic spot virus, or INSV, and the disease, Pythium wilt, have both been around for years. But warming temperatures driven by climate change are creating more hospitable conditions for thrips, the insect that carries INSV, to thrive.

“Over the last probably 10 years, we’ve seen milder winters, so that’s really allowed the population of thrips to build in our environment here,” said Jennifer Clarke, executive director of the California Leafy Greens Research Program, which operates under the authority of the California Department of Food and Agriculture. Clarke said INSV was first reported in the state’s lettuce around 2006, but was never so big of an issue as to pass any economic threshold.

California in particular is plagued by western flower thrips, according to Daniel Hasegawa, a research entomologist with the USDA’s Agricultural Research Service in Salinas. The tiny, slender bugs measure only 1 or 2 millimeters, so they can be difficult to spot and even harder to control, as they can hide in a plant’s folds away from the mist of insecticide.

Hasegawa said the thrips transmit INSV through feeding, much in the same way that mosquitos can transmit pathogens to humans. People won’t get sick from eating INSV-infected lettuce, but the plants will develop brown spots and areas of dead tissue.

“That’s the big question, as to what has changed. This virus has been around, but why has it reached some of the devastating levels that we’ve achieved this year?” Hasegawa said. Based on available weather and insect-monitoring data, “it seems like over the past 20 years, with the warmer temperatures, that the ability of the insects to develop during the wintertime is a lot more likely.”

The presence of Pythium wilt only added to the challenges this year, experts said. The disease is borne in the soil from fungi-like pathogens, which can rot roots and cause infected plants to wilt and collapse. Though many plant varieties are somewhat tolerant of Pythium wilt on its own, INSV can exacerbate it, Clarke said, “so we often see the two of them as a co-occurrence.”

It was the two in tandem that wiped out Salinas crops this fall, said Richard Smith, a researcher with the University of California’s Cooperative Extension program, which places agricultural advisers and researchers in local communities. While both have presented challenges to farmers in the past, something changed in the last few years to worsen the impact on lettuce crops.

Gary Coronado/Los Angeles Times

Farmworkers cull lettuce in Salinas, California.

In September, nearly all of California broiled under a record-shattering heat wave that lasted nearly two weeks — the sort of extreme heat event that researchers say will become more frequent and intense as the climate warms.

The shaky fall season was only the start of the challenge this year. Normally around December, the supply of lettuce transitions to southern desert areas around the Imperial Valley. But the disease problem in Salinas meant there was not enough lettuce to carry suppliers through that transition, said Christopher Valadez, president of the Grower-Shipper Association of Central California.

What’s more, those desert farms have been experiencing unusually cool weather that is delaying the maturity of the lettuce crops they do have. The Imperial Valley area has seen multiple freeze warnings in recent weeks, and lettuce is sometimes iced over in the mornings.

“Any current shortage in the supply of lettuce is a shortage in the supply of lettuce being produced from the desert production regions, like the Imperial Valley of California and the Yuma, Arizona, production region,” Valadez said.

“Moving forward, there’s a variable we can’t control, and that variable has been temperature,” he said.