Ag Alert Jan. 12, 2022

Chill Continued from Page 1

Creamer saidCitrusMutualmaintainsweather stations and a staff meteorologist to help growersmake decisions. For cling peach and nut growers, a point of concern is cold weather at bloom time, which is mid-February for almonds andmid-March for peaches. “At bloom time, anything below freezing is a problem, but if we’re in the 40-degree range, that’s fine,” Hudgins said. “Before theblossomsbegintoemerge fromthe jacket, it’s a nonissue.” Fedora said the same for his walnut trees. “Once the trees aredormant,wedon’tworry toomuch,” Fedora said. “They can take the frost. In the springtime, once the treebegins tomovesapintothe limbs, that’swhen wecan’t take it. That sapwill freeze, and that’swhereyou’ll get the frost damage.” Then there’s warmer winter weather, which can cancel out chill hours. A UC Davis chill-portion calculator sub- tracts chill units for temperatures above 60 degrees, and neither adds nor subtracts chill units for each hour the temperature is between 54 and 60 degrees. Jarvis-Shean said research points to chill portions as being amore accuratemeasurement. “There have been some years recently whenwe’ve had warm spells in the middle of winter, which can subtract fromchill accumulationwithinthe tree,” Jarvis-Sheansaid. “We’ve had some surprises in the spring, if you’re only counting by chill hours, because the trees have behaved like they didn’t get enough chill even though the chill- hours way of counting said that they did.” Phippensaidhedoesn’twant to seeany “warmJanuary afternoons” on theway to bloomseason. “If, today, it gets to 55 or 60 degrees, it’s exciting that tree again,” Phippen said. “That’s when you get bud swell and all that. Ideally, we’d like just to stay chilled all the way till bloom.” (Kevin Hecteman is an assistant editor of Ag Alert. He may be contacted at

Hudgins, chief executive of the California Canning Peach Association. “Our goal is to hit 800 hours between Nov. 1 and the end of February.” Hudgins tracks chill hours in Verona, Davis, Modesto andParlier. As of Jan. 3, he said, all except Daviswere run- ning behind their 2020-2021 levels. “Youwant the tree tobe inaperiodof dormancy before bloomso that it’s able togenerateacropat its full potential for the coming year,” Hudgins said. Insufficient chill time leads toanunevenbloom, “and thenyour crop is less than it could have been as a result,”Hudgins said. Coldweather isalsoacitrusgrower’s friend,uptoapoint. “I knowwe’ve had some colder temperatures, and a lot of peopleareconcernedabout subfreezing temperatures,” saidCasey Creamer, president of California CitrusMutual in Exeter. “We actually really like that. We’re always con- cerned about a hard freeze, but colder weather—between 28and32-33(degrees)—isactuallyreallygoodfor thetrees.” Creamer said winter dormancy helps to “color up the cropandpreserve thequality that’s there, andallows us to have a really good product throughout the year.” Citrus growers, especially in the Central Valley, are moving into peak-production season. Citrus is picked ac- cording to market demand, Creamer said, likening the presenceof coldweather to thedifferencebetweenstoring fruit inthe refrigerator andkeeping it onthekitchencount- er. When the quality is there, “we can pick to themarket,” Creamer said. “Having that good, cold weather allows us to hold the quality a little bit longer.” The point of concern for citrus is when temperatures drop below 28 degrees for multiple hours, Creamer said. Windmachines are onemeans of fighting such cold. “If there’s a good inversion—several degrees warm- er weather above the trees—those wind machines do a real good job of grabbing that warmer air and pushing it through thegrove,”Creamer said. Irrigating the treeshelps as well, as the water can help keep the groves out of the danger zone, he added.

Theremay be no suchworries this year, said Katherine Jarvis-Shean, a University of California Cooperative Extensionorchardadvisor inYoloandSacramentocounties. “We’re in a really great position with winter chill accu- mulation thiswinter,” Jarvis-Sheansaid. “We’rehaving the highest chill that we’ve had in the last seven years—even cooler than the2016-2017winter,whichwasour last pretty coldwinter.” Jarvis-Sheannoted that almondshave largely surpassed their needed chill requirement, “but for cherries, pista- chios, walnuts—we’re still in themiddleof winter as far as their counting is concerned. Soeverything looks good, but I would stay tuned.” Phippennotedwithoptimismthathisneighborhoodhas been foggy thiswinter, which is anadded chilling benefit. “The fog keeps the sunshine out of the orchard for a period in the morning, and so you get extra chill hours besides the evening,” Phippen said, explaining that the late-October atmospheric river stormwas a turningpoint. “We had a lot of fog following that, and I believe that’s right in the realmof the chill hours,” Phippen said. In the Sutter County town of Meridian, walnut farmer Brian Fedora is happywithwhat he’s seen so far. “I can definitely tell you that this is the coldest winter we’vehad insome time,”Fedora said. “Ourwalnut trees in theSacramentoValleyareverymuchasleep, logging those hours, and that’sagreat thing.”Chandler andHowardwal- nut trees need about 1,015 hours of chill time, he added. “I’m excited because we haven’t had good chill hours andgoodsubmoisture foracoupleyears,”Fedorasaid. “We also haven’t had great Chandler production. With these temperatures and this moisture, tome, if you’re going to predict, it shouldbe a very, very good year for Chandlers.” Cling-peach growers also arewatching theweather. “We’ve closed a lot of our deficit fromwhere we were a year ago, but we still have a fewmore to go,” said Rich



For the week December 30, 2021 - January 5, 2022 ETO (INCHES/WEEK)












BIGGS (244)

DAVIS (06)









.13 .16 .16 -11

.13 .19 .26 -60

.25 .33 .28 -7

.32 .37 .28 20

.28 .20 .21 36

.27 .24 .24 18

.29 .30 .22 24

.35 .25 .35 0

.39 .50 .51 -35

.56 .61 .46 33

W eekly reference evapotranspiration (ETo) is the rate of water use (evapotranspiration—the sum of soil evaporation and crop transpiration) for healthy pasture grass. Multiplying ETo by the appropriate “crop coefficient” gives estimates of the ET for other crops. For example, assume ETo on June 15 is 0.267 inches and the crop coefficient for corn on that day is 1.1. Multiplying ETo by the coefficient (0.26 inches x 1.1) results in a corn ET of 0.29 inches. This

information is useful in determining the amount and timing of irriga- tion water. Contact Richard Snyder, UC Davis, for information on coefficients, 530-752-4628. The 10 graphs provide weekly ETo rates for selected areas for average year, last year and this year. The ETo information is provided by the California Irrigation Management Information System (CIMIS) of the California Department of Water Resources.

For information contact the DWR district office or DWR state headquarters:

SACRAMENTO HEADQUARTERS: 916-651-9679 • 916-651-7218

NORTHERN REGION: Red Bluff 530-529-7301

NORTH CENTRAL REGION: West Sacramento 916-376-9630



Fresno 559-230-3334

Glendale 818-500-1645 x247 or x243

January 12, 2022 Ag Alert 17

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