Freezing temperatures on the mornings of March 10 and March 11, appear to have caused the most damage to California almond orchards in the foothills and the southern part of the San Joaquin Valley.

“We got through the frost situation pretty well,” says Joe Connell, University of California Cooperative Extension Farm Advisor for Butte County in the northern Sacramento Valley. He received reports of temperatures no lower than about 29 degrees. “Because growers here deal with frost more regularly than those in other areas of the state, they’re pretty well prepared for frost with their sprinkler systems. (The heat in water applied by solid set or micro sprinkler systems helps protect the trees.). We were right on the temperature edge where sprinkler systems do a fine job of protecting against frost.”

A little farther south, almond orchards in Yuba and Sutter counties also appear to have escaped mostly unharmed, says UCCE Farm Advisor Franz Niederholzer. “It didn’t get as cold along the Feather River as around the Sutter Buttes,” he says. “I haven’t heard of any freeze damage.”

That’s not the case in Stanislaus County where Roger Duncan, UCCE farm advisor, reports extensive damage in some areas. Temperatures of 27 degrees or even colder for two to three hours were common in this part of the San Joaquin Valley, he notes. Frost damage was spotty and varied with elevation. “I inspected one almond orchard where 80 percent of the flowers and small nuts were killed by the frost, while the damage was only 30 percent in an adjacent orchard. Other almond orchards in the same vicinity had very little damage.” A difference of 1 degree can make the difference between having a full crop or being wiped out.

Orchards with no weed growth and bare, moist soil to absorb solar energy during the day and radiate heat back to the trees at night fared better than those where weeds were allowed to grow 6 to 12 inches high. Such vegetation limits the ability of the sun’s rays to heat the soil, Duncan explains.

Bob Beede, Kings County farm advisor, says many areas within Kings and Tulare counties suffered frost damage since the temperature dropped to 27 degrees long enough to freeze newly set nutlets. Tree fruit was also hit.

“It will be a couple weeks before we know the full extent of any early fruit set damage,” he says. “Increased size of the remaining nuts can only partially compensate for the loss of the frost-killed nuts. Already there are indications that the frost may have cost the industry 50 million pounds or more in lost production this year.