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Once brought from Asia and Africa, the fern is devouring vegetation.

Cliff Sullivan's helicopter swept across a vast Florida wilderness Thursday, armed with spray nozzles and weed killer.

"When I turn and fly back, you'll see it all," he warned.

As he banked to put the sun behind him, a plant called Old World climbing fern stood out in the swampy greenery with the radiance of emeralds, even as Sullivan unleashed payload after payload of herbicide meant to kill it.

Scientists fear that the fast-growing fern, originally imported from Africa and Asia, will march across Central and South Florida like a botanical wildfire. It kills all in its path, strangling mature trees and trapping wildlife, from tortoises to wading birds and deer.

As exotic weeds go, the climbing fern is now public enemy No. 1 in Florida. Scientists predict it will spread across millions of acres of wetlands and forests, spanning from Orange County to the Everglades, in less than a decade.

The devastation caused by the plant was obvious from the bubble head of Sullivan's helicopter.

Nearly everywhere Sullivan turned above the St. Johns River headwaters in Indian River County, climbing fern was at work, encasing trees and bushes.

The shapes were strange, almost ghastly. Layers of fern, consisting of wirelike vine and small leaves, grow 3 feet thick. That blocks sunlight, ultimately killing trees and bushes. The sheer weight of the fern mats, plus the combined grip of vines, also snaps limbs from trees.

"The plant does that to get more sunlight," said Gary Nichols, who works for the St. Johns River Management District.

He and others who battle invasive plants have taken photos of wildlife in a death grip, including deer caught by their antlers.

Forest rangers have battled fires that intensified when flames raced up ladderlike ferns into the crowns of trees.

For the past several years, imports such as Australian-native melaleuca and Brazilian pepper have become two of the state's most infamous exotic plants, growing out of control in forests and wetlands across Central and South Florida. Now, scientists miss the day when those two were the prime concern.

In fact, state officials have already given up any thought of engaging in hand combat with the Old World climbing fern. The vegetation is too thick for boats, and the terrain too mucky or wet for hiking.

The fern is in "the middle of swamps, and you can't get to it," said William Haller, acting director of the Center for Aquatic and Invasive Plants in Gainesville. "It has absolutely the worst environmental impact."

That leaves the battle to helicopters. But even that strategy has limits.

The specific herbicide used to kill ferns is deadly to other plants as well. So spraying is limited to the coldest time of the year, when trees are dormant and not as vulnerable.

That meant water managers were able to spray only 12 days this year. Thursday was the last day for 2008.

"Out of herbicide and with no more spraying left to do, Sullivan took a last few passes over the infested area and pointed out areas that had countless sprigs of new-growth fern.

"We sprayed here three years ago," said the pilot.

For this year alone, the cost of the aerial assault was $130,000 to treat 2,500 acres. Meanwhile, an additional 6,000 acres of fern-invested wetlands were discovered on agency lands along the St. Johns River.

"Next year there's going to be a huge application," Nichols said.

The pest first showed up in South Florida plant nurseries in the 1950s and was found in isolated wilderness in the 1960s before it exploded in the 1990s.

Old World climbing fern covered 17,000 acres in 1993 and 100,000 acres in 2003, according to researchers. Using a computer model, they predict the infestation will cover more than 5 million acres in Central and South Florida by 2014.


Moths to do battle

Spraying isn't the only method being been used against this pest. Two agencies released nearly 30,000 moths this week, counting on their caterpillar offspring to devour the Old World climbing fern. An attempt with a different species of moth failed two years ago.