California Chill Report: Navigating Changing Chill Patterns

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Chill Patterns

Chill patterns have been shifting over the past 50 years as a result of a higher frequency of warmer winters. UC Cooperative Extension Orchard Systems Advisor, Kat Jarvis-Shean noted that “last year was a luxuriant chill year.” However, this year could be a marginal one for chill accumulation. To address problematic chill patterns, Jarvis-Shean has been researching dormancy-breaking materials like Dormex, seeking solutions for walnut growers.

“It wasn’t really high on people’s radar last year because we had so much chill,” Jarvis-Shean explained. “But as people are watching that chill counter and thinking about playing around with Dormex because it’s recently labeled, I would say that this is a good year to experiment on a small scale.”

The weather this year is more on track with the winter of 2019-2020 which did not end up as a good chill year for growers. Jarvis-Shean noted that a lot will hinge on how February goes. But growers have a potential tool to use to help offset the effects of a lack of chill accumulation. Jarvis-Shean said that Dormex is a viable option for growers to use as bud break approaches.  

“Thirty to 40 days [before anticipated bud break] is what I would target based on our experience so far,” said Jarvis-Shean. “Looking at different timings, that seems to be the most potent, effective time for Dormex to be applied.”

Information from the UC Davis Chill Calculator shows that as of January 16, the Durham CIMIS station has logged 47.3 portions under the dynamic model, with 430 hours below 45°F. The station in Manteca has registered 43.3 portions, with 608 hours. There have been 783 hours in Merced, with 41.3 cumulative portions. In Five Points, there have been 634 chill hours, equating to 40 portions. Finally, the CIMIS station in Shafter has registered 39.1 portions, with 651 hours.

Listen to the segment below.