The amount of chill accumulation that trees receive in California is expected to decline over the coming years. UC Cooperative Extension Orchard Systems Advisor, Kat Jarvis-Shean said that researchers are projecting a notable decrease in chill by 2040. Warmer winters are likely to become a more common occurrence, posing significant challenges for growers.
“I’d say orchards that are going in the ground right now or young orchards that are coming into bearing about ten years from now, they’re going to be expected often experience 10 to 15 percent less chill in their prime,” said Jarvis-Shean. “You’re stuck with those trees for quite a while. So, you can’t change that variety or its chilling requirement. But you can apply things to those trees to help compensate in those low chill years.”
Long-term approaches to address the issue include the development of new varieties that require less chill accumulation but can still achieve desired production levels. More immediate solutions to challenges related to chill are available now for growers. Jarvis-Shean has been working with materials like Erger, CAN-17, and Dormex to help mitigate challenges related to a lack of chill. “We found all three of those, in walnuts at least, are effective at helping trees wake up from dormancy earlier than they would have without some intervention,” Jarvis-Shean explained.
Information from the UC Davis Chill Calculator shows that as of February 28, the Durham CIMIS station has logged 70.5 portions under the dynamic model, with 917 hours below 45°F. The station in Manteca has registered 65.9 portions, with 763 hours. There have been 993 hours in Merced, with 65.3 cumulative portions. In Five Points, there have been 807 chill hours, equating to 62.5 portions. Finally, the CIMIS station in Shafter has registered 57.9 portions, with 786 hours.
Listen to the segment below.