It's not been a good year for Florida's citrus industry. The U.S. Department of Agriculture reports that, for the second year running, the orange crop is expected to be almost 10 percent lower than the previous year.

The culprit is citrus greening, a disease that has devastated Florida's oranges and grapefruits, and has now begun to spread in Texas and California.

Back in the 1950s and '60s, the Florida Citrus Tower was one of the Orlando area's most important tourist attractions.

"You could go up and see thousands and thousands acres of trees," says citrus grower Benny McLean. "And you could buy fresh-squeezed orange juice, or you could buy a bag of navels. So it was a big deal back then."

It all ended with a series of freezes in the 1980s that devastated citrus in Central Florida. In the '83 freeze, 300,000 acres of mature, fruit-bearing orange and grapefruit trees died in a single night. Growers eventually recovered by moving and replanting groves further south.

Citrus greening poses a similar crisis for growers, but one for which so far, there is no solution.

"I can't imagine Florida without commercial citrus," says Harold Browning, director of the Citrus Research and Development Foundation, an industry group that is focused almost entirely on one problem: defeating citrus greening.

The disease is caused by a bacterium that's spread by a tiny flying insect called a psyllid. Greening ruins the fruit, making it bitter and unmarketable, and eventually kills the tree.

Browning says the disease — which originates in Asia — was first discovered in Florida just eight years ago.

"Within three to four years, it had spread pretty much through all the producing counties in the state," he says. "And then with time and with the transmission by psyllids, it's filling in the gaps."

Scientists and growers now say virtually 100 percent of Florida's groves are infected with citrus greening.

Maury Boyd is a grower who heads the McKinnon Corporation, which has 1,500 acres of citrus groves. On one tree, near his office in Winter Garden, the orange is hard and shriveled. Lots more fruit has already dropped and is on the ground.

The bacterium that causes greening is hard to treat because it flourishes deep inside the tree, in its vascular system. Boyd says it disrupts the flow of the nutrients trees need to survive.

"See, I visualize it like your arteries, when you got plaque building up," says Boyd. "And then suddenly, you're not getting enough blood through on the other side."

When Boyd started seeing greening in his groves in 2006, he and his manager began scouring the scientific literature looking for answers. With the trees' vascular systems in trouble, they began spraying a solution containing vital nutrients directly on the leaves, called foliar spraying.

At the same time, he and other growers began an intensive campaign of pesticide spraying aimed at controlling psyllids.

It's a short-term strategy aimed at keeping diseased trees productive as long as possible. And for now, it seems to be working.

In one of Boyd's groves of Valencia oranges, he's been doing the intensive spraying. Many of the trees have branches with yellowed leaves and shrunken fruit associated with the disease. But large sections are productive, with plump oranges ready for picking.

It's a stopgap measure, and Boyd says one that comes with a high price: His costs went from about $750 an acre to about $2,200 an acre.

Boyd says as long as citrus prices remain high, he and other growers doing this intensive spraying may keep their heads above water. But unless scientists find a cure for greening, he says it's just a matter of time before economic realities and the disease force him out of the citrus business.

The industry, the state of Florida and USDA are spending millions of dollars each year funding research. And scientists have some promising leads.

At the University of Florida's Citrus Research and Education Center, Fred Gmitter is a horticultural researcher who's scoured groves throughout Florida looking for "survivor trees." He's now testing the root systems of 16 trees that may be resistant to citrus greening.

"We're not thinking that all 16 are going to be immune or resistant," says Gmitter. "But if one or two or four are, which of those 16 are those one or two or four? We don't know."

Gmitter says finding out which ones work and are commercially viable may take another four or five years.

While researchers have been making progress, the toll taken by citrus greening has grown dramatically recently. Dean Gabriel, a plant pathologist at the University of Florida, says that in the past two years, more and more fruit has begun dropping from weakened trees.

Gabriel has helped decode an important piece of the citrus greening puzzle — the genome of the bacterium that causes the disease. That work helped scientists identify the bacterium's potential weaknesses. They're now testing chemicals that they believe may help citrus trees fight back against the disease.

Using genetic engineering, Gabriel has also helped develop greening-resistant citrus trees. They've been submitted to federal regulators but final approval is still at least five years away.

As a scientist, Gabriel believes GMO citrus trees may be the best solution to greening. But as a realist, he knows many consumers — and citrus growers — are still leery about GMOs.

"You can have the best cure in the world, and if people are afraid of it for whatever reason, well, you just have to wait some more years and meanwhile search for another cure," says Gabriel.

But for Florida oranges and grapefruit, the clock is ticking. Citrus acreage is now nearly half of what it was in the industry's heyday.

If production continues to drop, many growers worry that soon there won't be enough critical mass left to support the industry infrastructure — the packing houses and juice processors that take Florida citrus from the groves to the breakfast table.

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