UC Agriculture and Natural Resources experts said the dip in yield cannot be blamed on the drought, but a warming climate may be coming into play. Pistachios require cold winter temperatures to reset their biological clocks.
“They use the temperature to know when winter is over,” said Craig Kallsen, UC Cooperative Extension advisor in Kern County. “And if they don't get the message, they get confused.”
Male trees then end up blooming after the female tree. If female plants don't get fertilized when they bloom, they still produce shells—just empty ones.
Kallsen said the hardest hit regions are in the Southern San Joaquin Valley.
"We're looking at a record low (yield)," Kallsen said.
Farmers to the north had more chilling hours, so they are seeing a normal or low number of empty pistachio shells.
Growers have found that spraying oil can help trees bloom more uniformly, however, it doesn't always seem to help, the story said.
“There are a lot of things we're still trying to understand,” said Gurreet Brar, UC Cooperative Extension advisor in Fresno County. “Oil applied at the wrong time or in inappropriate conditions like water stress conditions can injure the plant.”