Season-to-date, the San Joaquin Valley citrus crop has felt minimal pressure from below-freezing temperatures as compared to last year, according to a press release issued by California Citrus Mutual, based in Exeter.
Overnight temperatures Jan. 2 dropped to a season low of 27 degrees in the coldest areas; however, the cold weather proved manageable and no damage to either the Navel or Mandarin crops was reported.
The temperature threshold for mandarins is approximately 32 degrees for a duration of two hours, while Navel oranges can withstand cold temperatures as low as 28 degrees for a four-hour duration before frost-protection mechanisms need be utilized.
According to reports initiated by California Citrus Mutual, Mandarins have experienced 13-14 critical nights season-to-date, compared to more than 30 nights for the same time period last season. Only three to five nights of critical temperatures were reported season-to-date for the Navel crop, which experienced 24-25 nights at this point last season.
Growers ran wind machines on Mandarins for an average of 8-10 hours Jan. 2 vs. zero to five hours for the more cold-tolerant Navels. The use of wind machines and a warm inversion layer worked to keep temperatures in the groves up by about three to five 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. The citrus-producing areas 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, and there are a total of 16,300 wind machines at work in the Central Valley.
Overall wind protection cost in the Central Valley is approximately $550,000 per hour across the entire industry. The industry spent roughly $100 million on frost protection during the 2011-12 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. Generally, a strong sugar content within the fruit provides internal frost protection as well, and that is the case this season. In seasons of late maturity, such as last season, the fruit is much more susceptible to frost.