Posts Tagged: chill

Delving Deeper into the Concept of Supplemental Chill

Supplemental chill, also known as cold conditioning, takes place after harvest of the transplants, which have gone dormant because of their exposure to the decreasing daylength and lower temperatures of the nursery fields of Northern California where they are grown. Postharvest supplemental chill occurs in a constant near freezing temperature, in the dark and when the transplant has no to very few leaves left on it.

What supplemental chill is actually doing is breaking (reversing) plant dormancy, which sets into motion a series of metabolic events in the plant resulting in a promotion of vegetative growth and inhibition of new inflorescence formation. Petioles grow longer, leaf blades get bigger and more runners are formed as dormancy is broken through supplemental chill. All of this is consistent with the industry understanding that a longer period of supplemental chill results in more plant vigor, again meaning more vegetative growth and less fruiting. The challenge for the berry grower is to strike a balance between the vigor of vegetative growth and the fruiting which is greatly desired.

Growers already know this, but berry cultivars vary greatly in their sensitivity to the dormancy breaking supplemental chill. Generally speaking, short day strawberry varieties need very little – something on the order of one to three days - to break dormancy and in fact most become tremendously vegetative when chilled in excess over the recommended few days.  In contrast, day neutral varieties need substantially more days of chill, most often in the range of one to two weeks, to develop the normal balance of vigor and fruiting following planting.  Since longer periods of chill are associated with greater vegetative vigor, organic growers tend to chill their plants longer before planting, in the range of 30% longer, so as to enable the plant to handle less hospitable soil environments.

Warm-wet chill vs Sunny chill

People who care about chill might want to spend a moment on this as the article linked below refers to different qualities of environmental chill.

The following article is for pistachios, but conceptually the thesis applies to our berry culture on the Central Coast.

One to two decades ago, fog in the Central Valley maintained temperatures steady, oftentimes below the 45 degree threshold for chill accumulation, for longer periods.  This has been named "warm-wet" chill.

In recent years, however, the pattern has changed, to little fog and consequent cold nights below 45 degrees followed by clear sunny days well into the sixties.  Net result of this "sunny chill" has been buds breaking on the sunny side of the tree and no buds breaking on the shady side.  A comparison in strawberry would be more pronounced differences in plant performance on the warm side of the bed compared to the cooler; caneberries quite probably similar to trees in having lateral budbreak earlier on the side of the hedgerow facing the Sun.

Now, in 2016-17, it's even more complicated with warm rains and few days below 45 degrees at all.  Doesn't seem like there is a consensus on how this will play out in the spring.

http://agnetwest.com/2017/01/24/chill-hours-getting-complicated/

Thoughts?

 

H/T Bob Klein, Manager; Administrative Committee for Pistachios and UCCE Farm Advisor Craig Kallsen.

 

 

 

An Observation on Chill Hours Accumulated This Year and What to Make of Them

Since digging for strawberry plants destined for Salinas and Watsonville started at Macdoel just a few days ago, I thought it would be judicious to have a look at how many chill hours we've accumulated so far and what it means for additions to supplemental chill, especially for our day neutral varieties.

I checked with the Lassen Canyon nursery chill accumulator here: http://lassencanyonnursery.com/cumulative-chilling-hours-and-weather-conditions/ .

Looking at the data for Oct 18 of this year and running my calculations via the Utah model (which subtracts chill hours for temperatures realized above 60^oF, see previous posts), we have currently accumulated 325 units of chill. Given that last year's chill accumulation was 164 units and by most commentator's opinion a decent accumulation, 325 accumulated chill units this year is very satisfactory.

So what does this mean for adjustments on supplemental chill? Personally, I think growers may want to take the strong field chill in stride, and now look forward to what sort of winter we are going to have. Looking at the NOAA data, we are probably in for a weak “La Niña” system this year, which according to the “Color Outlook Maps” for temperature, we have something like a 40% chance of having slightly warmer than normal temperatures in November, December and January.

http://www.cpc.ncep.noaa.gov/products/predictions/multi_season/13_seasonal_outlooks/color/churchill.php

The question then is what sort of adjustment should or needs to be made to supplemental chill. It's actually not an easy question to answer, given the strong field chill.  Then again the odds of a slightly warmer than normal winter would give me some reason to err on the side of caution and go a tad longer than customary on the supplemental chill .

Farmers welcome cool San Joaquin Valley weather

When the National Weather Service announced that December 2015 temperatures were as chilly as "normal," farmers cheered. Many fruit and nut trees require cool weather to reset their biological clocks and ensure a healthy crop, reported Robert Rodriguez in the Fresno Bee.

Chill requirements vary by crop and variety. Some cherries, apricots, peaches and pistachios requiring a significant accumulation of cold weather to rest and then start growing again when the temperatures warm. For example, without a cold winter, pistachio trees get confused at the beginning of spring. 

"It is like the female flowers were ready to party, but the male flowers weren't around," said UC ANR Cooperative Extension farm advisor David Doll.

If male trees bloom late, the female trees won't be fertilized, and shells may come up empty.

Winter chill for 2015-16 is off to a good start, and farmers are hoping the trend will continue.

"January is the biggest chill month," Doll said.

Farmer Raj Iyer told Rodriguez that last year January temperatures in the 70s were part of a weather trend that cut his cherry crop in half.

"We have had a normal weather pattern since November, so hopefully we will be back on track to producing a nice cherry crop," Iyer said.

Hot Days and Cold Nights:: Comparison of 2015 So Far with Years Past

So the question now is, so what Mark, we're around 68 chill units accumulated as of September 22 in Macdoel, but what does that actually mean to me as a grower?  How does it compare to years past?

Fortunately, we can reference past year's chill accumulation and make just that comparison.

Again, this year up to September 23 (I'm adding in last night's numbers right now), we have 32 hours below 32^o F (0.0 chill units/hour x 32 hours), 153 hours between 33^o F and 45^o F (153 hours 1.0 chill units/hour), 170 hours between 46^o F and 60^o F (170 hours x 0.5 chill units/hour), and 188 hours over 61^o F (140 from 61^o F to 80^o F and another 48 over 81^o F).  Negative chill units will be from the 188 hour (which we multiply by a quarter to obtain an approximate range for temperatures from 61^o F and 65^o F), which gives us (188 x 0.25) 47 multiplied by -0.5 chill units/hour = -24 plus the balance of 141 multiplied by -1 chill units per hour = -141.  Adding -141 + -24 + 153 + 85= + 73 chill units accumulated so far.

Looking at the numbers for 2014, which we consider a pretty hot fall in Macdoel, the same calculations as above from 3 below 32^o F, 137 hours between 33^o F and 45^o F, 147 hours between 46^o F and 60^o F, and 256 hours over 61^o F (202 from 61^o F to 80^o F and another 54 over 81^o F) brings us to -13 chill units accumulated by September 23.   This squares with observations from the field in September 2014 that the plants were barely chilled at all.

Next, let's have a look at 2013, which has been described to me as a "normal" chill year.  Referring to the Lassen historical chill chart, by September 23, we experienced 10 hours below 32^o F, 127 hours between 33^o F and 45^o F, 208 hours between 46^o F and 60^o F, and 226 hours over 61^o F (181 from 61^o F to 80^o F and another 45 over 81^o F) which by using my calculations brings us to +34 chill units accumulated by September 23, 2013.

Conclusion; from the looks of it we are tracking right along and having a normal accumulation of chill in the autumn of 2015.

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