Season-to-date, California’s San Joaquin Valley citrus crop has felt minimal pressure from below-freezing temperatures compared to last year.

Overnight temperatures dropped down to a season low of 27 degrees Jan. 1 in the coldest areas. However, the cold weather proved manageable. No damage to the Navel or mandarin crops was reported.

The temperature threshold for mandarins is approximately 32 degrees for a duration of two hours. Navel oranges can withstand cold temperatures as low as 28 degrees for a four-hour duration before frost protection mechanisms should be utilized.

According to reports initiated by California Citrus Mutual, mandarins have experienced 13-14 critical temperature nights season-to-date, compared to over 30 nights for the same time period last season.

Three-to-five nights of critical temperatures were reported season-to-date for the Navel crop, versus 24-25 nights at this point last season.

Growers reportedly ran wind machines on mandarins for an average of 8-10 hours on the night of Jan. 1, versus 0-5 hours for the more cold tolerant Navels.

Wind machines and a warm inversion layer worked to keep temperatures in the groves up by about 3-5 degrees.

Coupled with a strong fog layer over citrus-producing areas, no frost damage was incurred, with the exception of minimal damage to mandarins in unprotected “fringe” areas.

Rain generally aids in warming the ground and increasing temperatures in the groves as well.

Fortunately, we have experienced a series of storms in recent weeks, which was not the case at this point in time last season when conditions were much dryer. 

The average cost to run a wind machine is approximately $30 per hour.  There are a total of 16,300 wind machines at work in the Central Valley.

Overall wind protection costs in the Central Valley are approximately $550,000 per hour across the entire industry. The industry spent roughly $100 million on frost protection during the 2011-2012 season.

There is in excess of 180,000 acres of citrus crops in the Central Valley with approximately 85 percent of the $2 billion crop still on the tree at this point of the season. This being said, a majority of the crop is exposed to the cold winter weather.

Generally, and as is the case this season, a strong sugar content within the fruit provides internal frost protection as well. In seasons of late maturity, such as last season, the fruit is more susceptible to frost.