Navel orange producers in California's Central Valley are expected to harvest 78 million 40-pound boxes this season, down from the 81 million boxes they harvested during the 2013-14 season.

Altogether, the state's navel producers are expecting a crop of about 81 million boxes, according to a U.S. Department of Agriculture forecast.

The predictions are based on a survey of representative groves conducted July 13-Sept. 2 in which fruit set per tree, fruit diameter, trees per acre, bearing acreage, and oranges per box were examined.

The estimate looked at conventional, organic and specialty navels, including cara caras and blood oranges.

The survey found fruit set per tree averaged 333, above the 5-year average of 328.

But individual fruit diameter was 2.2 inches compared to the 5-year average of 2.25 inches.

Last year at this same time, fruit diameter averaged 2.33 inches.