(UPDATED COVERAGE, Aug. 19) U.S. retail prices for fresh fruits and vegetables during July rose by the most in nearly three years, fueling accelerating food inflation that’s pushing grocery bills higher.

Average nationwide fresh fruit and vegetable prices during July rose 6.9% at retail compared with the same month in 2010, according to the Bureau of Labor Statistics’ monthly Consumer Price Index released Aug. 18. .

That’s the largest year-over-year increase for that category since a 7% rise in October 2008.

Rising produce prices partly reflect cold weather over the winter and spring that delayed harvests and curbed supplies of items such as beans, carrots and tomatoes, according to recent U.S.

“The weather has been the biggest culprit at this point, with an assist from energy-based inputs and transportation costs,” Gary Lucier, a U.S. Departmernt of Agriculture economist, said in an Aug. 19 e-mail. “All these products also have to be transported to market and with high petroleum costs, that  has added to retail prices as well.”

In the USDA’s July 29 Fruits and Tree Nuts Outlook, the agency said wet and colder than normal weather “extended the growing period for many of this year’s domestic summer fruit crops, delaying harvest this season. These delays contributed to the overall lightness of fruit supplies in late spring.”

Lucier added that although farm-level  fruit and vegetable prices account for only about a fourth of the retail value, “it is not clear to me that retailers have been passing on all the increases in farm prices we have experienced this year.”

Department of Agriculture reports. California’s cherry, strawberry and valencia orange crops are down from last year, the USDA said. Higher fertilizer, fuel and seed costs have also pushed prices higher.

Wet and colder than normal weather “extended the growing period for many of this year’s domestic summer fruit crops, delaying harvest this season,” the USDA said in its Fruits and Tree Nuts Outlook released July 29. “These delays contributed to the overall lightness of fruit supplies in late spring.”

July produce prices also rose compared with June, posting an increase of 1.2% to break a three-month string of declines, according to CPI data. For the full year, fresh produce inflation is on pace to rise 3.5% to 4.5%, the largest annual increase since 2008, according to a recent USDA forecast. Prices rose 0.6% last year after falling 4.6% in 2009.

Among specific products, red delicious apples averaged $1.37 a pound nationwide last month, up 3.8% from $1.32 in June and up 6.2% from $1.29 in July 2010, according to CPI data. Navel oranges averaged $1.08 a pound, up about 7 cents from June and but down 7 cents from July 2010.

Iceberg lettuce averaged 89.7 cents a pound, down from 96.7 cents in June but up from 85.3 cents in July 2010. Field-grown tomatoes averaged $1.44 a pound, down from $1.56 in June and down from $1.54 in July 2010.

Beef, pork and milk have also grown more expensive at the supermarket, contributing to food inflation that’s on track for the third- or fourth-biggest annual increase over the past 20 years, according to CPI data.

A broader price index reflecting food consumed at home rose 0.6 percent during July from June, the largest monthly gain since March. Compared to July 2010, prices for food at home rose 5.4%, the largest year-over-year increase since a 5.7% jump in January 2009.