Does pruning increase yields for almond growers?
Will the most sun lead to the healthiest trees and biggest crops?
These are questions that UC Davis professor Bruce Lampinen has spent years studying, and he shared that knowledge with almond growers in Fresno this month in a talk about canopy light interception and yield potential.
Over time, Lampinen’s tools for studying light interception have changed--his current setup includes a GoPro camera and GPS unit rigged to a scouting vehicle that drives through the orchard at seven miles per hour. It captures images and sends them to an iPhone app that counts pixels in sun and shade.
The ideal amount of light interception is around 80%, Lampinen told growers, producing about 4,000 kernel pounds of almonds per acre. Greater output of 4,500 kernel pounds an acre can be had with 90% light interception, but other problems arise.
“You start to have food safety issues after about 80% light interception because you can't dry the almonds on the orchard floor and the temperature is the ideal temperature for salmonella,” Lampinen said.
Lampinen also talked about the difference between east-west row plantings and north-south.
“East-west planting stayed very consistent through the day at test field, but you can't dry the nuts as well, there is food safety risk,” he told growers.
Pruning trial work
So, how does pruning influence yield potential? Lampinen described a Stanislaus County trial, now in its 14th leaf, that examined spacing and conventional pruning practices.
“The unpruned treatment has had the highest interception in the whole trial,” Lampinen said. “Pruning has not increased yield. Conventional annual pruning has reduced annual yield most years."
This defies common wisdom, Lampinen said, which is that almonds need to be pruned to manage light distribution. Instead, he said pruning actually exacerbates these problems. Pruning may decrease disease but if so, not enough to improve productivity in the trial.
“There are reasons to prune, but increasing yield is not one of them,” Lampinen said.
So why should growers prune almonds?
One reason is to allow the sun to reach the orchard floor. Others include worker safety and improving the visibility of the trunk.
Still, Lampinen made it very clear that pruning is no silver bullet.
“In conclusion, every pruning cut you make decreases yield,” Lampinen said. “Unless it's a dead branch you're pruning.”