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Henry A. Barrios / The Californian

Jennifer Stilwill with the Kern County Ag Commissioner's office holds up a cara cara navel variety orange that normally has a reddish color in this Dec. 13 photo. She points out that discoloration and spaces in the cut orange are indicators of freeze damage to the orange.

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Henry A. Barrios / The Californian

Cara cara navel oranges are sliced and ready for inspection for freeze damage at the Kern County Ag Commissioner's office Friday.

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Henry A. Barrios / The Californian

A severely damaged mandarin orange, right, is compared with one with very little damage, left.

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Henry A. Barrios / The Californian

Ag technician Gordon Beagley inspects mandarin oranges at the Kern County Ag Commissioner's office Friday.

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Henry A. Barrios / The Californian

In this Dec. 13 file photo, Jennifer Stilwill, supervising biologist, foreground, and Brian Gatza, ag biologist, background, inspect citrus for freeze damage at the Kern County Ag Commissioner's office Friday.

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Henry A. Barrios / The Californian

Spaces and discoloration in the cara cara navel oranges are indicators of frost damage.

While navel oranges were found to have fared relatively well through the recent hard freeze, mandarins gathered Tuesday from across Kern showed significant amounts of frost damage in preliminary testing Friday by county inspectors.

Four of six mandarin samples, each consisting of 33 pieces of fruit, exhibited enough damage to write off this season's production in the groves where the batches were picked.

The results are not binding: Official testing is done in packing houses after the industry has had an opportunity to cull damaged fruit. The true cost of the cold weather won't be known for weeks or months.

Kern County's citrus crop last year was valued at $629 million; about 31 percent of that total came from mandarins, which are marketed as Cuties and Halos.

The most widespread damage was found in mandarin samples gathered in the Rio Bravo and Arvin areas, said Jennifer Stilwill, supervising biologist in the county Agricultural Commissioner's office. She said samples from the Delano area also suffered substantial damage.

All six mandarin samples, from areas including Maricopa and Edison, showed at least some evidence of damage, she said.

Only one of 11 navel samples showed enough damage to taint an entire batch, while the only lemon sample suffered "quite a bit of damage" -- enough to write off the batch, Stilwill said.

But the findings are not representative, said Bob Blakely, director of industry relations for the trade group California Citrus Mutual. He said the county pulls samples from the areas it believes suffered the worst cold spells.

"They're kind of looking for a worst-case baseline," he said.

Packers have special equipment to test fruit for frost damage, he said, adding that the industry has a strong incentive not to ship tainted fruit.

On Tuesday, California citrus growers agreed to a voluntary fruit inspection program designed to keep freeze-damaged produce off store shelves.

Any citrus harvested after Tuesday is to be held for 48 hours to allow time for damage to become apparent and give county inspectors an opportunity to inspect it.

In place indefinitely, the program threatens unspecified penalties against packers who ship product before submitting a sample for testing purposes.

Blakely said many growers are waiting to harvest until enough time has passed -- several days in many cases -- that the fruit exhibits damage.

Growers are reporting minimal damage in some places, he said, with the worst losses being seen on the valley floor and areas where irrigation and wind machines -- measures used to raise temperatures in citrus groves -- were not available.

The citrus association reported Wednesday, near the end of the freeze, that growers have spent $32.4 million on efforts to protect the Central Valley's $1.5 billion citrus crop.