Growers said citrus is susceptible to damage right now because the fruit doesn't have a lot of sugar content yet.
The cold spell will further delay the harvest of navel oranges around the valley. The greener the orange the more susceptible it is to freeze damage.
For growers like David Stutsman of Exeter, running water through the orchard is a time-tested protective measure. Stutsman explained, "You can put it down during the day. You're just putting warmth in the soil and at the night the soil gives off its heat as the air gets colder so you're just adding a little temperature to the air."
Wind machines then help move some of that warmer air around. Stutsman will turn his machines on when it hits 28-degrees. The practice raises the temperature of his orchards. Stutsman said, "You can see it right away as soon as you fire those wind machines up. You can see a couple of degrees on a day with a very good inversion layer."
Bob Blakeley of California Citrus Mutual said the valley citrus crop is worth 1-point-billion dollars. Just two-percent of the oranges, lemons and mandarins has been picked. Blakeley said, "We're very exposed right now. Our harvest is late. We've harvested only half of what we normally have harvested at this time of year."
Blakely added the rain isn't helping, especially if the citrus doesn't dry out. He said, "Then that water on the fruit is another concern because if it freezes on the fruit it can cause rind damage later in the season."
Oranges with so-called "ice mark" can't be sold on the fresh fruit market.
Local growers say they can withstand two nights of really cold temperatures. But if the cold spell lasts longer, the chance of crop damage increases.