Update: Saturday, 8:45 AM: Unexpected cloud cover late Friday and early Saturday kept temperatures slightly higher than forecast, enough to prevent damage to most commercially grown fruit. Lows in most places were in the upper 20's. Forecasts call for more extreme cold over the weekend. ORIGINAL REPORT:
Valley citrus growers are in for a long night tonight, as what is expected to be the coldest evening of the year threatens to damage the region's citrus crop, with the most popular new variety, the mandarin orange, most at risk.
Temperatures are expected to drop into the mid to low 20's for an extended period of time, with lows from 22 to 27 degrees. In the coldest places temperatures could remain below freezing for as long as 11 or 12 hours, enough time to cause serious damage to fruit and to trees, according to Joel Nelson of Exeter based California Citrus Mutual.
"There's about 75 percent of the crop on the trees and that represents about at least $1 billion in value, so the growers are going to be up all night, monitoring the temperatures, making sure their equipment is working properly," says Nelson.
Growers are using wind machines and irrigation water to help raise the temperatures in their orchards by just a few degrees. By circulating the warmer air from up above, they hope to be able prevent serious damage. The last big freeze to damage the local citrus crop was in the winter of 2007, but since then, thinned skinned easy to peel mandarin oranges have replaced thousands of acres of heartier navel oranges.
"The mandarins are one of more susceptible varieties to cold damage just because they're thinner skinned. Lemons would also be placed in that category. The navel oranges are a much tougher orange to have frost damage occur, they're a thicker skinned piece of fruit," Nelson says. "But one of the advantages that both of those varieties have this time of year is that they're very flavorful, they have a high sugar content. And that in itself helps the fruit ward off frost damage."
So far this year, growers have been able to avoid serious damage, despite a string of cold nights. And Nelson says the fact that these cold temperatures are coming in January and not December is a big advantage.
"Because we're into January, the fruit has a tendency to adapt, and we've had a series of cold nights, and as those cold nights materialize, the fruit itself gets a little bit tougher, so it fights back internally. Mother nature has a way of doing that," says Nelson
Still the rapid growth of mandarin production presents a risk to growers. In 2007, sub-freezing temperatures from January 11-17, led to the loss of 27 percent of the state's navel orange and lemon crop. That freeze cost the state's agriculture industry an estimated $1.3 billion. Since then, new plantings of popular mandarin oranges have exploded.
"Five years ago we were harvesting about 12,000 acres of mandarin varieties. This year we're going to be harvesting something closer to 44,000 acres. It's a significant increase in the last five years. The industry is so excited about this variety of citrus, as is the consumer, that there's more acreage in the ground of young trees, and young trees are more susceptible to cold than your heartier, mature trees, so there's a lot on the line tonight, and tomorrow night as well," says Nelson.
In order to save their fruit, Nelson says mandarin growers have to run their wind machines more often.
"Traditionally we figure if it's 28 degrees for four hours or longer, we've got to run frost protection for [traditional] oranges, For the mandarin producer it can range from 30 to 32 degrees. We're going to try to elevate grove temperatures from three to five degrees, and hopefully it doesn't dip below that 25 degrees level and perhaps we can save most of this crop," says Nelson.
There is a bit of good news however. Nelson says that the most vulnerable varieties of mandarins have already been harvested. Most of the remaining acreage is the Murcot variety, which has a slightly thicker skin and better cold tolerance. He says his growers think those factors, and Friday's sunny conditions should help prevent a repeat of 2007's losses, at least for tonight.
"So the combination of frost protection and the maturity of the crop on the tree, we're cautiously optimistic that we can minimize the damage tonight," says Nelson.
The cold temperatures are expected to continue through the weekend.