Mild winters in recent years have been creating some dormancy issues in orchards that become apparent later in the season. Researchers have been evaluating different options that might assist walnut growers to overcome some of those challenges. UC Cooperative Extension Orchard Systems Advisor for Yolo, Solano, and Sacramento counties, Kat Jarvis-Shean said they have been looking at a couple of different products in a multi-year study.
“With funding from the California Walnut Board for the first couple of years and now we just started getting funding from CDFA, we’ve been looking at dormancy breaking treatments that get applied in about a month before anticipated bud break,” said Jarvis-Shean. “To help wake the trees up so that we don’t see these weird behaviors that you usually get with low chill.”
The project has included a set of trees that the researchers artificially heated up to simulate a lack of chill, as well as trees that received the necessary amount of chill. Jarvis-Shean explained that products used for addressing dormancy issues are yet to be registered, so the work is still in the experimental stage. The research showed that the trees had quite a response to hydrogen cyanamide, marketed under the name Dormex, within two years of the project.
“We saw a response in both the heated and unheated trees to Dormex,” Jarvis-Shean noted. “The following year, we tried Dormex again, but with a lower rate. So, four percent the first year, two percent the second year…and we saw again that hydrogen cyanamide was effective at waking the trees up earlier than they would if we had not interfered.”
The cooler temperatures in December have continued to add to the amount of chill the trees are receiving. As of December 21, the UC Davis Chill Calculator shows that the CIMIS station in Durham has registered 33.4 portions under the dynamic model, with 663 hours below 45°F. The station in Manteca has recorded 32.3 portions, with 602 hours. There have been 707 chill hours in Merced, with 33.1 cumulative portions. In Five Points, there have been 618 chill hours, equating to 30.8 cumulative portions. Finally, the CIMIS station in Shafter has registered 30.5 cumulative portions, with 610 hours.
Listen to the latest chill report below.