David Doll3 CommentsDecember 23, 2020Horticulture

Tracking Winter Chill in Fruit Growing Regions

Written by Franz Niederholzer1 and Kitren Glozer2 1UC Farm Advisor, Sutter/Yuba Counties, 2Associate Project Scientist, Department of Plant Sciences, UC Davis “Is it a good chilling year?”  That’s a common coffee house question this time of year in fruit and nut growing regions.  The amount of chilling a perennial crop accumulates in a given winter will influence bloom conditions – the most crucial time in a crop season.  Less chilling than a certain tree crop requires can lead to an extended bloom; too little altogether can result in bud death and drop in some crops like apricot and sweet cherry.  ‘Good chilling’ (more chilling than the minimum required) can produce a very short bloom season, or ‘snowball bloom’.  Chilling models can provide growers and their advisors with key information to time dormancy-breaking materials (hydrogen cyanamide, oil, etc.) to manipulate bloom to improve or maintain yield and quality in regions where local chilling is marginal for a certain crop.  Climate change may make achieving critical chilling more important in years to come.  In this article, we’ll briefly review chilling and chilling models.  Deciduous perennial crops break bud in the late winter or spring after a certain amount of cold weather (chilling) followed by a certain amount of warmer weather.  Think of this process as a relay race.  The chilling is the first leg of the race, and the heat accumulation is the second leg.  Bud break is the finish line.  The length of each leg of the race depends on crop and variety.  The weather during the race influences the runner’s speed.  Good chilling weather speeds up the chilling leg, warmer weather can slow it down or even stop it.  Cool weather on the warming leg slows the progress towards bloom.  Since most perennial crops are not native to North America,

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David Doll13 CommentsDecember 14, 2016Horticulture

Sun Reflecting Products for Increased Winter Chill? 

Written by Bob Beede (UCCE Kings County, Emeritus) and David Doll (UCCE Merced) Tests of winter applied kaolin clay or calcium carbonate-based materials intended to either reflect solar radiation or diffuse it continue.  Results from David Doll, UCCE Farm Advisor, Merced County, and Valley Orchard Management, showed an increase in chill portion accumulation and a 200 to 250 pound increase in CPC yield over untreated trees when kaolin-clay was applied prior to the 2015 season. More can be found here.  The data thus far suggests that spraying these materials to mitigate the negative effects of warm winter temperatures does not assure you of a normal crop, but it might prevent NO crop! This past winter, Carl Fanucchi and Bob Beede collaborated with ORCAL, the company which manufactures ultra-fine, dry ground calcium carbonate, which is marketed in liquid form as Mask® and Diffusion®. They performed UNREPLICATED screening trials in two locations; one in Buttonwillow, and the second east of Highway 99 on Pond Road.  The screening trials included single and double applications applied January 12 and February 12.  A December treatment was planned, but the field could not be accessed.  Flower bud temperatures were monitored in treated and untreated areas using tiny thermocouples inserted into the buds without causing their death.  The resulting data showed bud temperatures were reduced by as much as 100F, and the rate of heating during the morning hours was also slower.  Calculations indicate that the January treatment increased chill portion accumulation by about 13%, due to the lower bud temperatures.  Weekly rating of the treatments for bud break and bloom were also performed.  The treated trees emerged more evenly, and the second treatment of Diffusion applied in February delayed development by four to five days.  The single January treatment developed at about the same rate as the untreated. 

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David Doll3 CommentsDecember 14, 2016Horticulture

Winter Chill Update: December 2016

Written by Bob Beede, UCCE Kings County, Emeritus. Editors note: This article was developed with high chill crops, particularly pistachio. Almonds aren’t as chill dependent, but the broad topics discussed are relevant to all perennial horticultural crops. Those of you who are outside every day know that it has been pretty warm.  The only cold weather occurred during the first week of December in which many locations within the Central Valley experienced three to five days of temperatures ranging from 30-320F.  The Colusa CIMIS station reported 260F the morning of December 6.  Table 1 provides the chill portions for various sites throughout the Valley between September 1 and December 13 for the past four winters, as well as 2010 in which over 70 chill portions were accumulated by February 15.  This exceeds the 58-60 chill portions estimated to satisfy the rest requirement of the Kerman cultivar. The Peters male may have a chill portion requirement as great as 65.  The values in parentheses are the total chill portions accumulated by station and year.  2013 and 2014 were significantly warmer than 2010, in which dormancy was well satisfied throughout all areas of the state.  The 2015 data shows good chill accumulation was well on its way throughout the Central Valley in mid-December, and continued cold temperatures through January contributed to the record 2016 crop.  In contrast, 2014 was already showing deficient chill accumulation at several locations by mid December.  The Arvin/Edison and Coalinga stations might be considered the “canary in the coal mine” for early assessment of future low chill winters.  As you can plainly see, chill portion accumulation is not good thus far, and in some locations, less than the 2014 winter. Table 1. Chill portion accumulation for various CIMIS stations statewide from 9/1-12/13 for selected years. Numbers in parentheses are

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