FRESNO, Calif. (AP) -- With California's temperatures slowly climbing, citrus growers say they have seen little crop damage after a sixth night of very cold weather.

California Citrus Mutual Director of Grower Services Paul Story said Wednesday that temperatures warmed up by a few degrees in the San Joaquin Valley overnight Tuesday.

Growers have spent $28 million in frost protection measures over the past six nights. The week-long cold spell has caused damage primarily to the mandarin crop.

Story said growers have deployed wind machines and sprinklers, elevating grove temperatures well above 31 degrees. Prolonged temperatures in the mid-20s or below can cause damage to citrus crops.

The unusual chill could translate to a slight bump in per-carton costs, but won't impact retail prices or supply.

Approximately 75 percent of California's citrus crop remains on the trees.

Copyright 2013 The AP.