Nat Roberts watched with sympathy as Hurricane Charley (search) blew in from the Gulf Coast three weeks ago and ripped through groves in southwest Florida, causing losses of up to 20 percent for next year's Florida citrus crop.

The hurricane spared Roberts' property, safely located across the state on the Atlantic Coast, but his 4,000 acres of grapefruit and orange groves now face a similar danger from Hurricane Frances (search).

Frances threatens to devastate the Indian River Citrus District (search), a strip of land stretching 200 miles from Daytona Beach to West Palm Beach. The area produces about three-quarters of Florida's $205 million grapefruit crop.

"Nobody would have thought of this happening on both coasts," said Roberts, general manager of Callery-Judge Grove in Palm Beach County.

The double whammy of Charley and Frances has the potential to cause the greatest crop damage to Florida's $9 billion citrus industry since the crippling freezes of the 1980s, industry officials said.

Because they are a heavier fruit, grapefruit are more vulnerable than oranges to being blown off trees.

"We're a month away from harvesting and the grapefruits are a good size," said Doug Bournique, executive vice president of the Indian River Citrus League, a grower's group. "When the winds whip up around the trees, it's easy to twist off."

Any damage to the grapefruit crop would be felt globally because the state dominates the national and international market, said Thomas Spreen, chairman of the Food and Resource Economics department at the University of Florida.

"A significant loss in Florida takes a significant chunk out of the world supply," Spreen said. "From a consumer standpoint, it would have a very strong effect on the price of grapefruit."

Charley, which swept through some of the state's biggest orange-producing counties in southwest Florida, caused estimated losses of $150 million.

Depending on Frances' path and intensity, the hurricane, along with damage from Charley, could alter Florida's citrus industry in ways that the freezes in central Florida did in the 1980s, said Casey Pace, a spokeswoman for Florida Citrus Mutual, the state's largest grower's group.

The freezes, which caused hundreds of millions of dollars in losses, damaged thousands of trees. Many growers who lost crops abandoned citrus and sold their land to developers.

Orange groves were replaced by new housing developments and strip malls in the fast-growing areas around Orlando as the citrus industry moved to warmer temperatures further south.

Some of the same dynamics could play out in the Indian River district, where development pressure is coming from South Florida residents who have migrated north into Palm Beach and Martin counties.