*Florida crop could shrink 12 percent in 5 years -growers

*Greening disease has wiped out one county citrus industry

(Adds quotes, details, byline)

By Jane Sutton

BONITA SPRINGS, Fla., June 25 (Reuters) - Florida's orange crop could shrink by about 12 percent, to 140 million 90-pound boxes, within five years as the state battles the tree-killing disease known as greening, an official with the state's largest growers group said on Thursday.

"One could think that we might drop to the 160, 155 million boxes as early as next year, so 140 (million boxes) could be in the next, certainly, three to five years," Michael Sparks, executive vice president of Florida Citrus Mutual said at the group's annual conference in Bonita Springs, Florida.

The 2008-2009 harvest, which ends next month, is forecast at 159.6 million boxes, down from 170.2 million last year.

Growers are awaiting a September tree census to determine how many acres of citrus groves have been lost to greening. It was first discovered in the state in 2005, just after a parade of hurricanes battered the groves, and has spread to all 32 of Florida's citrus-growing counties.

"If we don't beat greening, we simply don't have a product to sell," Sparks said.