Years of low chill have been increasing in frequency over the past 50 years. UC Cooperative Extension Orchard Systems Advisor for Yolo, Solano, and Sacramento counties, Kat Jarvis-Shean said the overall trend has been towards warmer winters. Until now there have been limited options to mitigate the issues that arise from a lack of chill accumulation. Several different problems can occur in years with inadequate chilling, particularly in walnut orchards.
“When we get low chill years, that can mean some buds don’t even break on the tree,” Jarvis-Shean explained. “That could mean some buds that come out later, or a wider window of bud break which can then often result in having a multiple shake year, or even having a little bit left in the field even after your second shake that just doesn’t warrant circling back to pick up.”
To help growers avoid those types of challenges, a multi-year research project has been evaluating materials to break dormancy in walnuts. Jarvis-Shean said that hydrogen cyanamide, marketed under Dormex, has demonstrated strong potential. “Dormex was just maybe three weeks ago labeled for walnuts in California. It also last year got labeled for pistachios. So if you’ve been looking at the Dormex label, make sure you get a very up-to-date label from end of January, early February of this year,” Jarvis-Shean noted.
Information from the UC Davis Chill Calculator shows that as of February 23, the Shafter CIMIS station has logged 70.8 portions under the dynamic model, with 1,264 hours below 45°F. The station in Five Points has registered 69.8 portions, with 1,293 hours. There have been 1,386 hours in Merced, with 74.3 cumulative portions. In Manteca, there have been 1,205 chill hours, equating to 73.9 portions. Finally, the CIMIS station in Durham has registered 75.7 portions, with 1,315 hours.
Listen to the latest chill report below.