Faced with a possible loss of harvesting efficiency when shaking large circumference pistachio trees, machine fabricators have upped their game.

“They are making them more robust and have improved the shaking patterns,” says University of California researcher Louise Ferguson.

Known for her work in the mechanical harvest of table olives, Ferguson was funded by the California Pistachio Research Board to work on alternative harvest techniques to improve the harvesting percentage of pistachio nuts.

What has not changed since she began her research with a direct contact harvesting head is the challenge of removing a high percentage of in-shell split nuts from very mature pistachio trees.

A limited trial in 2009 showed that traditional shaking left an average of 38 percent of the in-shell split nuts per tree. Later trials showed improvement with experimental shakers which averaged 96 percent, but only in trees with a truck circumference of less than 50 inches.

In larger trees, the efficiency rates for all shakers tested decreased.

Hermilo Esquivel, manager with Erick Nielsen Enterprises (ENE) in Orland, Calif., says their shaker operators are able to change the shake pattern frequency to be more effective with larger trees. ENE manufactures pistachio harvesting equipment and also operates a custom harvesting business at Orland.

He says adjustments can be made by machine operators during the shaking process as they determine what works best for each tree. Depending on the age of the orchard at harvest, shakers can be set up to improve harvest efficiency.

Besides the modifications in the harvest machinery, growers are addressing the trunk size challenges by decreasing the height of the tree and performing selected pruning cuts to maintain a more upright growth pattern in the scaffold branches. Topping and selected hand cuts can improve light interception and tree shape.

Ferguson says some pistachio growers are also attempting ‘circle tying” young trees to train major scaffold branches more upright.

There is no data that this type of training either enhances or hampers the shaking process, Ferguson says. There is a bonus however as it keeps the fruit within the catch frame of the harvest machinery.

The theory is that the more upright the tree the higher shaking efficiency. Nuts growing closer to the vertical axis of the tree are more likely to come off than nuts growing on lateral branches and much more likely than nuts on low-hanging branches.

The tree training can be done the first seven years after planting with light mechanical pruning beginning in the fourth or fifth years. Hedging depends more on the growth of the trees if they meet across the row. Trees should be shaped for the space available, says Ferguson.

Tree spacing has not changed for the dominant Kerman pistachio variety, but Ferguson says it could for some newer varieties including Lost Hills and Golden Hills which are more upright.

Looking at the thousands of acres of new pistachio trees planted across California, Ferguson is also thinking about how to harvest the earliest nut crops before the trees can tolerate mechanical harvest. She is referring to 4-6 year-old-trees that bear some fruit but are not mature enough to handle shaking. This is where her direct contact harvesting head might work, Ferguson says.

The direct canopy contact head is modeled after the original “Studer” style shaking head used in mechanical olive harvesting trials. The vibrating rubber-clad fiberglass rods rake through the branches shaking nuts off as the head moves across each tree. The passively pivoting head moves along the sides of the trees and reaches toward the centers to remove the nuts.