EXETER, Calif. — Domestic shipments of California valencia oranges should hit stride between late May and mid-June as the state’s navel deal winds down.

Demand could dip by late summer, then finish with a bang in late September or early October thanks to the school lunch push, said Bob Blakely, director of industry relations at Exeter-based California Citrus Mutual.

Some growers were picking valencias for export in late March, said Claire Smith, Sunkist Growers’ director of corporate communications. Southeast Asia was the top destination for spring exports.

The state’s navel deal ends in late July. Volume for the 2010-11 season is expected to finish at 1.86 million tons, according to the U.S. Department of Agriculture. That’s up 17% in a year. Valencias are forecast at 520,000 tons, down 5,000 from a year ago.

California’s valencia acreage stands at 41,000, down 2,000. There’s been a steady decline since 1999-2000 when there were 71,000 acres, according to the USDA.

“Valencia acreage is continuing to drop as it loses popularity to offshore imports,” said Bob Blakely, director of industry relations at Exeter-based California Citrus Mutual. “By summer we face stiff competition from navels and mandarins from the Southern Hemisphere. Navels (there) are the preferred fresh orange, and they have taken a lot of the valencia market.”

Sunkist Growers, for one, was bucking the acreage trend.

“Our acreage is very similar, and we are showing production per acre up about 5% on average from last year,” Smith said.

Sunkist’s lemon crop — grown year-round — should reach in the neighborhood of 600,000 tons in 2011, she said.

“Lemon production is slightly higher than last year,” Smith said. “It may become significantly higher as we expect a proportional increase of larger sizes … due to the heavier precipitation many lemon growing areas received this year.”