(UPDATED COVERAGE, Jan. 17) The bill for saving California citrus from six straight nights of freezing temperatures is unlikely to be passed on to consumers, but it may take weeks to clarify the extent of losses.

The industry spent $28 million on anti-frost measures — wind machines and water — in the Jan. 10-15 cold snap. The state’s crop is valued at $2 billion.

“Per carton prices may rise slightly, but the price per pound at retail should not be impacted,” Joel Nelsen, president of Exeter-based California Citrus Mutual, said in a news release. “Consumers will not see any impact as far as quality of the fruit either.”

As milder temperatures returned, early assessments showed only isolated areas of damage to mandarins.

No measurable damage to the 63 million cartons of navels still on trees was reported.

For mandarins, no significant threat emerged until the fourth night, Jan. 13, when temperatures dropped into the low- and mid-20s. That’s colder than frost protection measures can fully compensate for.

“With protection we were able to get it up to 29 (degrees), which is good for navels,” said Alyssa Houtby, director of public affairs at California Citrus Mutual. “For mandarins, 32 degrees is about as low as they’ll go. We’re expecting some damage in the mandarins.”

Lemons too are less resistant to cold than navels, and expected to face some losses.

Still, damage for the season to date is likely to pale in comparison to freezes last year and in 2007. A comparatively mild winter has boosted sugar content, providing the fruit some insulation.

Expensive as the week was for growers, they remained well below last year’s prevention costs — $100 million.

“Growers will be out assessing the damage for the rest of the week,” Houtby said Jan. 14. “There may be moderate damage to the mandarins, and minimal damage to navels on the borders of protected areas.”

Growers were working with California Department of Food and Agriculture inspectors and country agricultural commissioners to assess damage and keep affected fruit off the market.

Groves closer to California’s coast — in Ventura and Riverside counties, for example — were spared Jan. 13, the coldest night. On the same day in the San Joaquin Valley, growers started their wind machines around 9:30-10 p.m. They’ve spent about $17.5 million on frost protection, compared to $100 million at this point last season.

On Jan. 14, temperatures averaged 26 degrees in the San Joaquin Valley, but the machines boosted those three to five degrees and put the fruit above critical level. Some damage appeared likely, however, in Imperial County where citrus is less tolerant of cold.