The University of California Cooperative Extension recently hosted a walnut pruning trial field day at Castle Farms near Atwater. Attendees were shown some of the progress that has been made in the pruning trial, as well as other important information related to walnut tree nutrition and disease management.
“We established two different treatments out here. One being the conventional way of pruning walnuts, where we head them back somewhere around six feet and then we prune annually…that is in comparison to what we call an ‘unheaded treatment,’ in that case we establish the orchard and after the first year growing we remove all the in-season branching off the tree,” said David Doll, Cooperative Extension Pomology Advisor for Merced County. “Then instead of heading back at six feet we actually leave it unheaded, or untipped, and we let that tree remain.”
After six years of observation, the trial has demonstrated some interesting results related to yield. “It actually allows the tree to develop fruitwood earlier in the orchards life and with that, we found an increase in yield…the yields were slightly higher, consistently in the unheaded trees, in which we ended up with a higher cumulative yield over the first four harvests,” Doll noted.
The early yield differences between headed and unheaded trees appear to be leveling out as the orchard continues to mature. “In the sixth, seventh, eighth leaf they’re yielding similarly so that gain is all coming from allowing that fruitwood to develop earlier in that tree,” said Doll.
There are several similar trials taking place in other parts of California, which are also demonstrating comparable results. “The less we prune these trees in the beginning, the more crop we set up earlier…the cropping patterns will eventually probably be the same, but they are a little bit different because of the response to those wounds on those younger trees,” Doll said.
Other topics of the walnut pruning trial field day included information on Botryosphaeria management within walnut orchards, along with management of nitrogen and potassium as well as leaf sampling procedures. Attendees were also presented with a demonstration of how a pressure chamber is used for walnut leaves.
Listen to Doll’s interview below.