Pistachio harvest ended earlier than usual this year, but growers should not stop irrigating their orchards just yet. The early finish creates a longer post-harvest period before trees enter dormancy, making proper irrigation especially important.
Research by Daniele Zaccaria, Mae Culumber and Anderson Safre of the University of California Cooperative Extension indicates that pistachio trees continue using water after the nuts have been removed. Although harvest is complete, evapotranspiration—the loss of water from the soil and through the trees’ leaves—continues until the trees become dormant.
Because the post-harvest season will be longer this year, growers should continue monitoring their orchards’ water needs. Stopping irrigation too soon could place unnecessary stress on trees as they prepare for next season.
However, the researchers suggest growers may be able to conserve water through carefully timed deficit irrigation. This practice involves applying less water than the orchard would normally use during selected periods. When managed properly, deficit irrigation may reduce water use by about 20% with little to no effect on the following year’s harvest.
The key is timing. Growers should consider orchard conditions, soil moisture and the trees’ water needs before reducing irrigation. An early harvest does not mean water use has ended, and post-harvest management can play an important role in supporting the next crop.
Read more about the research in the September issue of Pacific Nut Producer Magazine.