Minimal pruning boosts walnuts
Limiting irrigation water reduced need for tree pruning
By TIM HEARDEN
ARBUCKLE, Calif. -- In a test of how young walnut trees respond to certain pruning methods, researchers affirm it may not be necessary to cut them back as much as many farmers do.
In an orchard near here, University of California Cooperative Extension farm advisors are finding that trees that are minimally pruned have so far yielded the best tonnage per acre.
"The lowest yield is the heavily pruned one," farm advisor Carolyn DeBuse told nearly 100 growers during a workshop March 6. "The other three treatments were not a significant difference, but the largest yield is the minimal-pruning low-vigor (method)."
By low vigor, DeBuse means the researchers cut back 25 percent on the trees' irrigation to postpone the need for early hedging, which would save growers on costs, she said.
The UCCE is in its fourth year of testing the different pruning techniques on hedgerows of Chandlers and other walnut varieties commonly grown in the Sacramento Valley.
At a similar workshop last year, researchers said they found that many trees that were trimmed sparingly or not at all had produced a bigger yield of nuts than trees that were cut more aggressively. In the 2011 harvest, the minimally pruned trees again performed the best.
"There's ... a thought that if you don't prune them, they won't grow," DeBuse said. "We didn't have that problem."
DeBuse and other farm experts reiterated that it's still early in their research and proper pruning levels can depend on many factors, including soil and overall farming practices in an orchard. DeBuse also cautioned growers not to abruptly stop pruning trees that they have previously pruned more aggressively.
By last November, trees that were minimally pruned with low vigor yielded an average of 2.41 tons per acre, while trees that weren't pruned at all yielded 2.23 tons per acre, By contrast, heavily pruned trees provided only 1.64 tons per acre.
The information was useful to David Scheuring, a walnut grower from Yolo County, Calif.
"It's interesting to get out in the field with the farm advisors and look at trees and see these things actually implemented," he said.
University of California Cooperative Extension walnut research: http://walnutresearch.ucdavis.edu/