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.
Great article out of the ubiquitous Wall Street Journal transcribing an interview with Tadashi Yanai, the billionaire behind the speciality clothing manufacturer Fast Retailing Co., who also operates the more than 1,700 Uniqlo stores in Asia and not incidentally oversees tremendous sales over the Web as well. This guy is very successful and we can assume he has a good idea of what's up.
Why I am writing about clothing retailers on this on an ostensibly berry science oriented blog? Here's why. Mr. Yanai refers to the meaning of data, and what to do with it which as my readers know is a pretty big theme here. Data is not the end all for acquisition of knowledge; one actually needs to apply real insight, both from education and experience, to make it work.
Here's what this very successful businessman has to say about it:
"Data would never substitute the merchant. How do you interpret the data? That's the merchant's skill set. You need to uncover the insight that is buried in the data and the merchants need to uncover it. Even if you employ artificial intelligence to help you, the numbers [don't tell] the future."
There you have it. Guess what all, you can't farm from just a computer, you actually need to know the meaning of the numbers [and that takes hard work].
As we creep towards strawberry planting season on the Central Coast, it is always good to review where we stand currently on nursery cold conditioning, and with this in mind, think about adjustments to the post harvest supplementary chill based on what sort of winter we might be expecting.
Those of you who know me understand my faith in hedging my bets and planning for contingencies. I favor decisions with a high probability of success and decent outcomes over swing for the fences with blow your socks off results but missing and failing most of the time. Short supplemental chill times with early planting dates to get the beat on the competition are not my thing since this strategy puts good plant vigor at risk, especially if this 2017-18 winter is warm.
Chill accumulation for this year looks good at the nurseries up at MacDoel. Using Lassen Canyon Nursery's chill accumulation chart (also appreciate the comps to previous years- very useful), shows that, after a warm start in September, hours have really ramped up and currently as of October 5 we are at 337 total hours according to my Utah model calculations (which subtracts chill during warm weather episodes, and discounts temperatures under freezing - look elsewhere on this blog for how I am doing this). That compares very well with previous years, and is in fact ahead of many of them.
Further, looking forward to what sort of winter we are to expect, let's go to the NOAA weather maps. Quite simply, for all of our strawberry production areas, it is as of now 40% probable that we get temperatures above normal this winter (being December, January and February). This is up from 33% a few weeks ago, so I am sensing a trend which seems to confirm where we are headed.
In conclusion, with solid field chill already in the can but a good probability of a warmer than normal winter in the offing, I would again this year favor just a little bit more supplemental chill than customary.
Nobody can say we shouldn't have seen this coming.
In the current NAFTA renegotiation, the thriving berry industry (88,000 acres representing a fivefold increase in one decade to 1.26 billion dollars in sales) of central Mexico has come into focus as an unfair competitor to US growers, enjoying cheap labor, state subsidies and year round growing conditions.
Interesting to see also the differences in attitude on this question between large growers, who operate in all three NAFTA signatories, and small growers who produce only domestically.
Good article, paywall protected though.
Attached is the latest iteration of the grower guidelines a number of us at UC Cooperative Extension have written and have had published by the California Strawberry Commission.
Super timely since planting is right around the corner, this piece on anthracnose in strawberry caused by the pathogen Colletotrichum , was written by myself, Steven Koike and Oleg Daugovish. It was then reviewed by our strawberry science colleagues Gerald Holmes, Kelly Ivors and Jenny Broome. Translation into Spanish (attached below) done by the Commission's Ariel Zajdband into pitch perfect Spanish in a single hour. The Commission's Joy Jacobs kept the project moving and she and Mercy Olmstead brought it over the finish line.
I'm really very proud of this team effort to put the latest settled science on a serious disease into the hands of growers, PCA's and industry people. I am privileged to work with such a great team of people!