Pistachio trees age much like humans — they get taller and their girth expands as the years pass.

Maturity changes in pistachio trees may necessitate alternative harvest techniques to maintain efficiency as the trees grow older. Traditional trunk shakers remove a smaller percentage of marketable nuts as trunks grow in diameter and canopies spread out. Older trees of some pistachio varieties also sustain trunk damage as they grow older.

The California pistachio industry is still relatively young and University of California Cooperative Extension pomologist Louise Ferguson says growers should be prepared for challenges that come with aging trees.

Ferguson and harvesting equipment manufacturers are studying harvest alternatives, including different shaking patterns of trunk shakers and a using a direct canopy contact harvesting head design originally developed for mechanically harvesting olives.

Ferguson, who has done extensive research in mechanically harvesting olives, said a limited pistachio harvest trial conducted in 2009 showed traditional shaking left an average of 38 percent of the in-shell split nuts per tree.

Another evaluation in 2010 did find higher efficiency rates with the trunk shakers. Four commercial harvesters and two experimental machines were used in the trial. The commercial machines averaged 83 percent efficiency while the experimental shakers from Erik Nielsen Enterprises averaged 96 percent. These were all in trees with trunk circumference of less than 50 inches.  Above 50 inches, the efficiency of all shakers tested decreased.

When harvest efficiency falls off in older orchards, growers can replant the orchard. However, Ferguson the costs and time it takes to regain production could make re-evaluating trunk shaker patterns and looking at alternatives economically feasible.

After trials in some of Paramount Farming’s Kern County pistachio orchards, Ferguson was optimistic the direct contact harvesting head could remove a high percentage of marketable nuts.

“It will work, but it will take some modification — both with the mechanics and the trees,” said Ferguson. “Where there is contact, we’re getting good removal. Where there is not, nuts remain on the tree.”