Jul 21, 2021
Last fall’s freezing weather will reduce walnut harvest

Farmers are walking orchards and assessing damage to walnut trees and potentially this year’s crop, which farm advisors say stems from periods of extreme cold that occurred last fall.

University of California Cooperative Extension (UCCE) farm advisors in several counties where walnuts are grown commercially report that “winter dieback” or “winter kill,” brought on by below-freezing temperatures last November, has affected walnut trees young and old.

“Some trees are really wiped out and only had some leaf-out in spring from the bottom of the tree, and in other orchards symptoms might have some shoot dieback at the very tops of the tree,” said Luke Milliron, UCCE farm advisor for Butte, Glenn and Tehama counties. “In many orchards, damage has really delayed leaf-out and the leaves are really small, which means that these orchards are at a real risk of sunburn with the extreme heat.”

Organic walnut grower Paul Lauenroth, who has about 50 acres of walnuts, pointed out that damage to county walnut orchards is widespread.

“I’ve rode around into different areas of Lake County, and I was quite surprised. Some orchards are fair and other orchards are definitely not worth picking. We have a big crop with damage to the trees that’s unbelievable,” Lauenroth said. “Some trees are loaded so much they look like they’re going to break, and then you go to the next tree and it looks dead, then the next tree is half loaded and the next tree is loaded. I’ve never seen anything like it.”

Lauenroth said he believes this will also affect the operation of his commercial walnut dryer, which typically runs six days a week during harvest.

“The walnut dryer is affected big time,” Lauenroth said, adding that he believes due to lack of volume his walnut dryer may only run one day a week. “Many affected walnut orchards do not have a crop. The crop is really light; it’s maybe 50%.”

Ken Mitchell, who grows walnuts in Sacramento County, said he has observed only minor damage to his walnut trees this year.

“Our damage is 3-5% damage. The tree dies except all of the way down to the stump, and then the tree comes back as just wild growth,” said Mitchell, adding that reasons for the tremendous amount of damage are not totally clear. “Two or three years ago we personally had damage from frost that was pretty devastating. We had to cut a good number of trees back, probably 50-70% down, just to get live growth.”

Farm advisors believe that the cause of freeze damage to walnuts is related to wild swings in weather that happened in November 2020. In early November, temperatures were around 80° F, and they dropped well below freezing on Nov. 10 and Nov. 12. UC Davis plant physiologist Maciej Zwieniecki explained that during the warm daytime temperatures, limbs contain starch, which does not provide protection from freezing. 2020 is the third consecutive year of walnut freeze damage in California, according to farm advisors.

Freeze damage, which was first observed in the spring, is most severe in Butte, Glenn and Tehama counties, Milliron said, with other damage reported in Lake, San Joaquin, Stanislaus, Yolo and Yuba counties.

Lake County farmer David Rosenthal, who was not directly affected since he does not grow walnuts, said he was surprised by the scope of the damage to Lake County orchards.

“Driving through Lake County, the trees look dead,” he said. “These look like old, abandoned trees that have been dead for some time, but the reality is they were all alive last year and now they’re not.”

Rachel Elkins, UCCE farm advisor emeritus, Lake and Mendocino counties, reported that some orchards have been through several consecutive years of drought-related winter injury events. In visiting orchards, she said, trees with better water status going into the fall and winter, mainly due to irrigation, were more likely to emerge from dormancy in better shape.

Lauenroth said, “There seems to be no rhyme or reason” for the sporadic nature of the damage across the orchard.

“If all of the trees froze, you’d think they’d all be the same, so to see one tree good and then the next tree bad and two trees good and two trees bad, it’s so strange,” he said. “I went up to the highest part of the orchard and there’s more dead trees there than anywhere else in the orchard. I guarantee that highest spot didn’t freeze.”

Due to the damaged walnut trees, those in the walnut business expect reduced yields for this year’s walnut crop, with some orchards “more severely reduced and maybe years of recovery for those blocks,” Milliron said.

“I wouldn’t expect to necessarily see any problems with the overall (crop) numbers. There’s a lot of new acreage coming online,” Milliron said.

Michelle McNeil Connelly, executive director and CEO at California Walnut Board & Commission, said the walnut sector will have a better estimate of this year’s walnut production following the release of U.S. Department of Agriculture California Walnut Objective Measurement report on Aug. 27.

“It is incredibly hard to tell at this point what the impact of the freeze is on the overall crop, as there is no consistency in what is being seen across regions and microclimates,” Connelly said. “We will know more as CASS (California Agricultural Statistics Service) begins work for the objective measurement.”

The 2020 California walnut crop was about 780,000 tons, up from previous years due to increased plantings that happened over the past seven years, with the majority happening between 2013 and 2016, according to the California Walnut Board & Commission. California walnut acreage is about 380,000 bearing acres.

– Christina Souza, California Farm Bureau Federation
Image: Lucy Llewellyn Byard


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