By Vicky Boyd
Faced with triple-digit temperatures for much of July, county agricultural producers scrambled to reduce heat stress and keep their crops, animals and workers safe. But some admitted it was a challenge.
San Joaquin County Agricultural Commissioner Kamal Bagri said she hadn’t received any calls from producers about heat-related losses, but her staff surveyed several to remain up to date on conditions.
“The dairy guys have seen a little bit of downtick in milk production and their heifers getting pregnant,” she said. “But they didn’t think mortality has increased because they have better ways to cool their cattle since 2006.”
Bagri was referring to the 2006 summer heat wave that resulted in more than 25,000 cattle and more than 700,000 poultry dying statewide, overwhelming rendering facilities.
Based on recent surveys, she said some growers reported young silage corn fields being cooked by the heat as well as poorer quality alfalfa hay. In addition, she said she was worried about the walnut crop, particularly the early Tulare variety, based on the heat-related damage that occurred in September 2022.
According to National Weather Service data, the mercury topped 100 degrees 12 out of the first 13 days of July at the Stockton Airport. On July 6, Stockton even set a record for that date of 111 degrees, but it was still a few degrees off the all-time record of 115 degrees set on Sept. 6, 2022.
During the first half of July, many nighttime temperatures also remained in the 70s compared to the normal 60s. And forecasts called for more 100-degree days later in the month. Normal temperatures for the first half of July are in the mid-90s.
The July heat waves prompted National Weather Service and the San Joaquin County Office of Emergency Services to issue several excessive heat warnings that resulted in city cooling centers opening. Many growers also changed their workers’ schedules to keep them safe and out of the hottest parts of the day.
“We pretty much had them coming in at 5 a.m. and going home at noon,” said Lodi-area winegrape vineyard manager Joe Valente. “It was only seven hours. It was just too hot, and the workers understood it’s for their own protection.”
More frequent irrigations
Faced with high temperatures, Escalon almond grower Herman Doornenbal irrigated his orchards more frequently – two to three times per week – but with shorter sets. He said he felt fortunate to get water from the Oakdale Irrigation District, which years ago converted to a water ordering system similar to on-demand that offered more flexible scheduling. Some other districts use a rotating system where water is delivered on a set schedule and duration.
He considered water an essential nutrient required for life, and his trees responded well to the more frequent irrigations.
“I do believe that anything you grow, whether it’s a calf or cow or trees or tomatoes or rice, you have to give them the nutrition they need,” said Doornenbal, San Joaquin Farm Bureau second vice president. “The people that really haven’t cut back on nutrition, I believe they’re fairing better than the ones who have cut corners and because with this heat, the trees need everything they can get.”
But the frequent watering did create some wet spots in low orchard areas that delayed or prevented them from conducting normal cultural practices, like mowing. Doornenbal didn’t consider mowing to be essential, unlike spraying.
With almond hull split beginning in mid-July, he had to time his irrigations around the crucial navel orangeworm hull-split treatment to ensure the ground was dry enough to support sprayers.
“We had to back off on irrigations an extra day or two so we can spray, but as soon as we’re done spraying, the water goes back on,” Doornenbal said.
Paul Sanguinetti, who grows row and tree crops near Stockton, said he farms mostly heavier ground, which tends to hold water better than sandier soils. That helped him keep up with irrigations during the heat, although he shortened his drip sets on his processing tomatoes and baby lima beans and increased the frequency.
“Plants don’t like it when it gets hot, and they want to turn themselves off,” said Sanguinetti, California Farm Bureau District 12 board member. “We have to keep them hydrated, maybe irrigate a little closer together to make sure they don’t get too dry.”
He said having buried drip irrigation for his row crops also allowed him to fine-tune water application better than furrow or solid-set sprinklers.
Too soon to tell
Brenna Aegerter, a University of California Cooperative Extension farm advisor for San Joaquin County, said it’s too soon to determine the heat’s impact on the processing tomato crop. But she said it will likely affect fruit set and ultimately yields.
“It’s not good,” Aegerter said. “I think what we’ve seen historically is when there are really hot years, tomato yields are down statewide.”
It’s not just the high daytime temperatures that affect plants but also high nighttime temperatures, she said. During cooler nights, plant respiration slows and energy is conserved. But when nights are hotter than normal, plants have little down time and continue to respire, using carbohydrates that normally are stored and would eventually go toward crop production.
In mid-July, Aegerter was already receiving calls from processing tomato growers wanting her to look at fields that were beginning to go down. She said she suspected it was a combination of high temperatures and Fusarium, a soilborne fungus that affects a plant’s water-conducting tissue.
“Fusarium is our top challenge, and it’s definitely exasperated by the heat, and we have both things going on,” she said. “Vine decline may happen anyway, but it would have happened three weeks from now under more normal conditions.”
In checking his winegrape vineyards July 15, Valente said he only saw a few scattered burned leaves and didn’t notice any fruit damage. In fact, he said he saw more heat damage to vines last year because the temperatures quickly flipped from cool to hot with little chance for acclimatization.
This year, he pointed to a few 100-degree days in June as well as many in the 90s that allowed the vines to become better conditioned to warm weather before the July heat wave.
