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Attack of the Killer Weed

A sprig mug shot of Florida's Public Enemy Number One: Old World climbing fern.
Peggy Greb

In the 1979 science-fiction film Alien, the crew of the freighter ship Nostromo lands on a harsh and barren planetoid to investigate a distress signal. It discovers the remains of a starship that had crashed, perhaps eons ago, its crew mysteriously wiped out. Quivering in the ship's cavernous underbelly are thousands of translucent pods, and to the crew's bloody undoing, they bring a hatchling back to the mother ship.

The creature turns out to be remarkably adaptable, making hay (and lunch) out of most of the crew, all the while growing mightier and craftier. Meanwhile, the ship hurtles through space to some new destination where this alien, the so-called perfect organism, will acclimate, consume, and propagate.

Florida's Everglades are now battling their own version of that interstellar invader, an exotic plant so formidable that some researchers have nicknamed it "The Perfect Weed." Lygodium microphyllum, commonly called Old World climbing fern, has become Public-Land Enemy Number One.

The spore-spawning fern is native to most of the tropics in the Eastern Hemisphere, but the Everglades environment has acted as a virtual steroid. As insidious as it is beautiful -- it was brought to the state as a lawn ornamental decades ago -- the fern is a churlish megalomaniac, an herbaceous Donald Trump.

In a relatively short time -- scientists date the beginnings of the fern's encroachment to the late 1970s -- the climbing vine has blazed its way through the northern Everglades. Once it gains a foothold beside native plants and trees, it smothers them with a dense tangle of string-like vines more than a yard thick. After the trees below have died, they crash to the ground under the immense mass of the fern.

Even if the trees underneath manage to hold out, the vines are the perfect kindling for the natural fires that periodically move through. The heat kills everything nearby.

Researchers predict that if the fern's pugnacious ways were left unchallenged, it would within a decade cover almost all of South Florida's natural areas. And billions of spores were likely set free by last year's hurricanes, turning South Florida into a hothouse.

Without intervention by wildlife agencies, Florida faces the prospect of having its beloved Everglades, with their 1000 or so species of native plants, turned into a vast nursery for a tough, wiry weed that spreads its spores across the landscape like a confetti storm.


Unfortunately for the Everglades -- the only ecosystem of its kind on Earth -- Old World fern may be its worst enemy at the moment, but it's far from its only foe. An estimated 50,000 species of exotic plants have been introduced into Florida. Only Hawaii has more invasives.

The Florida Exotic Pest Plant Council lists 68 invasive species, including Old World fern, that are currently displacing native plants. Almost all of them are found in South Florida, from the familiar melaleuca tree and Australian pine to the exotic catclaw mimosa and woman's tongue.

State and federal agencies have long attempted to manage them through burning, cutting, and spraying herbicides. Many of those involved in the eradication effort, however, now recognize that the best long-range solution is biocontrol -- introducing the plants' natural enemies -- those little predators who munch away at the invasives in their native habitats. For example, there are now legions of bugs and fungi, imported by scientists from their Australian homeland ten years ago, laying siege to melaleuca in parts of Broward County.

The first salvos against Old World fern were launched this year with the introduction of leaf-eating moths at Jonathan Dickinson State Park and the Loxahatchee National Wildlife Refuge in Palm Beach County.

But halting the rapid spread of a fern as wily as this one is a desperate race against time.


On a hot, humid Friday just before Memorial Day, Stefani Melvin zigzags her airboat through the standing waters of Loxahatchee National Wildlife Refuge. The sanctuary's biologist, Melvin slows every so often to check GPS coordinates. Scores of white egrets, cormorants, and herons launch into the sky from atop tree islands. The occasional wood stork flaps lazily away.

Six miles out, Melvin nudges the boat beside a small patch of bushes and small trees rising out of the water. "This is how it starts," she says.

There's the enemy, the hungry marauder that threatens to eat the Everglades.

Old World fern looks deceptively meek. Its lavish leaves are bright green and slightly curly, oblongs the size of a gelcap. They fit tightly together on the stem, which is a woody string possessing surprising strength. Compared to the trunk of a full-grown tree, the stem feeding the plant's leaves is a puny toothpick.

Only when you tug on the leafy top vine do you get a sense of the threat. Already, the fern has built a deep layer of woody, leafless vine beneath its veneer of fluffy leaves.  

The climbing fern is well on the way to covering this SUV-sized island. "It's going to kill that wax myrtle tree it's growing on. It's like wire -- really tough stuff."

Trying to pull that tangle off the wax myrtle is like pulling a dozen scared cats off a shag carpet, so entwined has the killer plant become with its host. Melvin once found a deer that had made the mistake of running into a thicket of the fern. The deer struggled to its death with its front leg ensnared in the mesh.

Melvin, an easygoing woman with short blond hair and a deep tan, aims the boat to a nearby large tree island that became host in February to a colony of Australian moths called Austromusotima camptonozal, the first bioagent released in the battle against climbing fern. She steps off into the sawgrass ridge and follows a narrow clearing up to the tree line. "This might be an alligator trail," she warns. "Other times of the year, we could probably walk this, but they probably have a nest at the end of that trail. The females will definitely defend the nest, so I try to stay out of their way."

But the killer weed is as much a threat to that nesting alligator as to native plant life, Melvin notes.

Tree islands are as essential to Everglades fauna as a shoreline is to sandpipers and clams. Minute elevations in sea level in the Everglades -- often from small limestone plateaus -- give shrubs and trees a chance to take root where the water would otherwise be too deep. Over time, the roots and falling leaves build up and increase the elevation, so that the larger islands stay fairly dry even during the wet season. Deer, raccoons, panthers, and, of course, those nesting gators make the shady underbrush their home. Birds nest in the treetops and dine on the seeds and berries.

It's no exaggeration to say that without tree islands, the Everglades ecosystem would collapse. "Anything that needs dry ground relies on the tree islands," Melvin says standing in the blazing sun.

Old World fern wipes out tree islands.

It's hard to see it at this water level, but the tree canopy on this island, like many in the preserve, has collapsed under the immense weight of the climbing fern. "It's like this big donut, and then from there it grows out and over the trees on the outside," she says. "It becomes a huge mound of Lygodium." Indeed, aerial photos of these islands look like pro football arenas covered in green: the middle is flattened to the ground, then sweeps sharply upward at the edges.

State and federal agencies are already spending millions of dollars a year on herbicides and machete campaigns in a tough, slogging war against Old World fern. At best, the eradication campaign is slowing the weed's expansion.

But scientists are pinning their long-range hopes on the doughty little Australian moth that can't get enough of the insidious fern.

State naturalists had traveled to Japan, Southeast Asia, and Australia, finding more than 18 species of herbivores that dine on Lygodium. They spent $1 million and seven years looking for, testing, and permitting this first, single moth in order to release it in South Florida. The bright-white, wispy creature is a mere half inch wide from wingtip to wingtip and decorated with wavy brown streaks. Its adult life is short -- three to five days -- but the species' prolific females can lay 100 eggs at a time.

The moth's reign of terror against Lygodium, however, comes during its early life as a caterpillar whose hearty appetite strips the leaves into skeletons. Eating Lygodium exclusively, they can kill small plants and seriously damage the larger ones. If future testing goes well, they'll be joined by a mite, which also eats leaves and promotes plant disease, and another fern-hungry moth.


If alien plants such as Old World fern are barbarians at the gate, then the Invasive Plant Research Laboratory is among the best lines of defense in this long, weedy war. Tucked amid a plethora of college and technical school campuses to the southwest of Davie Road and I-595, the new quarantine lab is dedicated to finding the right bugs and diseases to maim and kill the worst invaders.

The man in charge is Ted Center, who wears a short, grayish, groomed beard and speaks in the slow, deliberate cadence of a man who's used to explaining the complex to the unlearned. The research leader's eyes are world-weary -- or perhaps it's just the fatigue of the ongoing move into the new digs.  

"There are very few facilities of this quality in the world," he boasts of the lab, which is owned by the U.S. Department of Agriculture, his employer, but sits on University of Florida property. He should know: "I went all over the world to look at every quarantine facility to see what went right, what went wrong."

The lab isn't under full quarantine yet but should be fully operating by midsummer. It's like a set from the Andromeda Strain -- except the airtight isolation zone is for foreign bugs instead of an interstellar virus. The entrance is a series of antechambers with magnetic doors that don't allow passage until all others are sealed. Insects imported to the lab are kept in a receiving room until they've produced offspring, which are then transferred inside. The original bugs, as well as any original packaging, are then destroyed. The air in the lab is filtered heavily enough to prevent any insects or spores from escaping. All liquids drain into a heated sump that destroys anything living.

Five living-room-sized greenhouses are attached to the general quarantine lab, which is where routine work is done. To reach the maximum security lab, which is for work on plant diseases, you must pass through yet more safety chambers. There are 13 doors between the outer world and this inner sanctum, with an eerie, muffled clank signaling you've earned the clearance to move through the next door.

"We can't work with viruses or bacteria, but we can work with fungal pathogens, which is mostly what we're interested in," Center says. "They [federal environmental authorities] will give us permission on a case-by-case basis."

The building is a huge leap forward for the dozen entomologists, plant pathologists, and ecologists working here on biocontrol. Until now, these researchers have used two small greenrooms at the University of Florida in Gainesville. "It's been incredibly productive," he says. "They've developed over 20 biocontrol agents in maybe the last 25 years. But it was small and too far away. With the invasive species problem getting bigger and bigger, we needed more space."

They will now be able to test several, maybe up to a dozen, kinds of insects at the same time. "Before, we had to do it one at a time," Center says. "Our limitation had been space and funding; now, it's manpower."

Center opens a large glass door into a greenroom, where one of the first experiments is under way. A score of young melaleuca trees rise up a yard in small black pots. Clinched around their leaves are a series of screen cylinders. Inside is a particular breed of fly that carries within it minuscule worms. The two carry on a mutually beneficial relationship: The fly lays eggs inside the buds of the melaleuca, which is a source of food for the larvae when they hatch. But the fly also inserts the worms. This tricks the tree into believing that the hungry worms are part of its blossom system, and it steps up the amount of nutrients it's sending to the buds.

In essence, the tree wastes valuable photosynthesis energy on swelling buds that will never bloom because the fly larvae will consume the buds after birth.

The payoff for the enemies of the melaleuca is that the tree's ability to bear seeds is largely stymied.

"We recognized very early on that basically a dead tree and a nonreproducing tree are the same thing, from a biological standpoint," Center explains. "If it's not producing seed, it's not doing any harm. You don't really have to kill the tree to control it."


Biocontrol has a long and reliable history. Aquatic invasives were targeted in the 1960s, primarily because few herbicides are licensed for use in water. Alligator weed, a green, spaghetti-like plant, was a particular problem for boaters and fishermen. "Three insects were introduced to control it," Center says. "Within a few years, it was no longer a problem, although it's still a problem in the Mississippi Valley, where it gets too hot for these insects to survive. Alligator weed is still here at a low level, and so are the insects. When the alligator weed pops up, so do the insects."

Center's work with biocontrol began with aquatic nuisances, such as water hyacinth, a free-floating plant with beautiful flowers; and hydrilla, a submerged vine. One insect eventually released on hydrilla offered a hard lesson on just how specialized these herbivores are to their native terrain. In this case, the scientists, after years of testing and seeking government approval, released an Australian weevil that feeds on the stems of the hydrilla.  

"This weevil looked really effective because it would burrow down the stems, mowing them off four or five feet below the surface," Center recalls. "We tested it; it was safe. We released it, never saw it again." That happened repeatedly. What they eventually surmised was that the weevil larvae continued down the stem to the lake bottom. The species had apparently adapted to extreme wet/dry seasons in its outback homeland, so that when its larvae become fully grown, they just wait for the water to dry out -- a seasonal extreme that doesn't occur in Florida. So it's back to the drawing board.

Still, even if you find the right bug for the right place, biocontrol takes patience. Although it's a very general rule of thumb, establishment in the wild is considered successful only after five generations have come and gone -- which is judged simply by the amount of time that's passed. It can take years to build up enough insects to reach a critical mass that can debilitate its host plant. And some insects just aren't as inclined to spread as others.


Melaleuca has long been recognized as a problem in South Florida, but it's now the poster boy for biocontrol success.

Like so many invasives, it was brought here from Australia as an ornamental lawn tree in the early 20th Century. With waxy green leaves the size of a small banana peel, it was fast-growing and made an excellent, full hedge. Nicknamed the paper-bark tree, it's far from attractive once it reaches maturity, however, when its whitish bark peels off in onion paper-like sheets.

It quickly made its way into the wild. Nurserymen helped the spread after realizing that they could save a lot of time by sowing the seeds in marshes rather than in planters. One early nurseryman chartered a plane and dumped cupfuls of seed onto the marshes. In the 1930s, it was spread aerially over the Everglades in the mistaken belief that it was a way of drying up "useless swampland." It grows extremely fast. Center recalls seeing the trees reach 20 feet in 18 months in ideal growing conditions.

By the 1950s, melaleuca had become a problem tree. Once it catches hold in an area, the trees form a jam-packed canopy that shrouds the understory in near darkness. Nothing grows beneath the thickets -- except for small melaleucas. An acquaintance of Center's recalls once seeing a spooked deer run toward a melaleuca stand only to bounce off because it was so dense.

The trees alter the landscape of the Everglades, especially when it comes to fire, which is a natural part of the ecology. Normally, the wildfires are "cool," which doesn't kill the native plants. But when the flames hit melaleuca -- which didn't evolve with the fires -- the flames become intense as they catch the paper-bark tinder and kill everything near it. The charred melaleuca drops its seeds -- roughly 60 million from an average tree. Native vegetation has a hard time competing with it.

Largely in response to the melaleuca and a handful of other invasives, the Florida Exotic Pest Plant Council was formed by control agencies, plant nurseries, and environmentalists in 1984, and it soon held a symposium that included the Agricultural Research Service, which is the U.S. Department of Agriculture's in-house research arm. "Most of the people involved originally had an environmental motivation," Center recalls. "Some economics followed because the only way they could control melaleuca was to cut a ring at the bottom of each individual tree and use full-strength herbicide. There could be 10,000 trees to an acre, and the cost was $4 a tree. So you were talking about $40,000 an acre."

The USDA had already established a lab in Australia as part of the hydrilla biocontrol effort. "Our funding was running out for that, and we had staff over there, so we just changed gears to look for bioagents for melaleuca," Center says. More than 400 species of insects feed on the tree in Australia, and the researchers began narrowing down the field to insects that would eat only melaleuca. The tree contains the same kinds of oils as a eucalyptus tree; these oils are basically a defense against herbivores, so anything that eats it is usually quite specialized. That's good, because it reduces the chances that the insects will be interested in Florida's native plants.

Far from being a crap shoot, it's quite predicable what insects will eat, Center asserts, as he opens a thick scientific treatise called Insects on Plants. "People get the idea that we're going to release an insect and it'll eat up the melaleuca and then it'll go eat everything else that's green. That's not the case. If it takes out the plant it feeds on, their populations usually crash." He estimates that biocontrol scientists worldwide have released about 300 species of insects against roughly 150 species of plants -- with virtually no unintended consequences.  

In 1997, a grayish weevil that looks a bit like a minuscule horny toad was released against the melaleuca. A plant lice, which in its nymph form sucks the tree's juices and injects it with a toxic juice, was released in 2002. If you wonder how anything so small could ever lay low hundreds of acres of 200-foot melaleucas, Thai Van and Min Rayamajhi have developed an outsized show-and-tell. Plant physiologists with the lab, they've been monitoring an experiment for eight years just west of Highway 27 in Broward County. A sweeping stand of melaleuca has overgrown scores of acres owned by a utility company, which has killed many trees with herbicide. New saplings are eagerly shooting up to replace them.

In the center of the property, however, lies a roughly 20-acre section that's been left untreated. Deep inside is the test plot Van and Rayamajhi routinely monitor to measure the effects of the bioagents.

They weave their way about 50 feet into the thicket. "Look at this one," Rayamajhi says as he grasps a small melaleuca shrub with a rusty color on the leaves. "It got hit by disease, and it's trying to grow back. The rust is disease. This one got hit by weevil."

Van picks up what looks like a miniature brown cob of corn. This is the melaleuca seed fruit. Each of its hundreds of "kernels," which are the size of a needle head, can hold about 400 seeds.

Even the tallest trees are at risk from the good weevils. As trees grow bigger, they require more nutrients via photosynthesis. Thus, a large canopy of leaves is essential. "The food production goes down because the insects feed on leaves and disease hits the trees," Rayamajhi says. "The tree diverts its energy to fight the insects, and then it doesn't have enough food to reproduce. Then they'll die. People wonder how little bugs can kill these big trees, but they're actually very vulnerable."

It's been enough to convince even skeptics that bioagents are a real alternative to spraying. "We needed to convince the state agencies that this was a long-term alternative to chemicals," Rayamajhi says. "At the beginning, we didn't have the funding to disperse the insects, but now they've reallocated some of the chemical funds to insects."


In late 2000, John Volin, an infectiously energetic plant scientist at Florida Atlantic University, began looking at the steady growth of Old World climbing fern. Little was known about its biology. Not until 1978 was its spread scrutinized by two scientists, who found it growing near the shoreline in southern Martin and northern Palm Beach counties. They concluded that the spore-bearing plant was a cause for worry.

No one got worried.

The fern, however, spent the next 15 years diligently establishing itself in the undergrowth beneath trees, then climbed upward, finally coiling around branches and leaves. Starved of sunlight, the trees slowly died. The South Florida Water Management District, a state agency that's a frontline warrior against invasives, began aerial surveys of the fern in 1993 from coast to coast at 500 feet above treetops. By the end of the decade, the water district had data indicating that the fern had spread to Florida's west coast and was overwhelming the tree islands of the Loxahatchee National Wildlife Refuge in south Palm Beach County.

What, Volin wondered, was the Everglades facing?

Using the data collected between 1978 and 1999, Volin devised a computer model to project the spread of the climbing fern by the year 2014. Despite knowing how rapidly the plant had multiplied, what Volin found stunned him. The model revealed the fern covering almost all of the Everglades in Palm Beach, Broward, Hendry, and Collier counties. Substantial portions of Martin and Glades counties will be smothered, and the infestation will have made deep inroads into Everglades National Park in Miami-Dade County.

Volin's findings seemed too dire to be true. "I said, 'Hell, we can't share this,'" Volin recollects. So before announcing the findings in 2002, Volin and his research assistants double-checked the reliability of his prediction through painstaking marches through the Everglades. "I feel strongly that, as a physiological ecologist, when we're doing predictions -- whether it's about climate change or, in this case, an invading species -- you don't want to overstate it," Volin says. "It's like saying the sky is falling. You don't want to do some dire prediction only to eat your words later on."

No one's calling Volin a Chicken Little.  

Don Schmitz, with the Florida Department of Environmental Protection's invasive-plant bureau, estimates that state agencies spend more than $2 million a year to combat Lygodium, about eight times more than five years ago.

The Loxahatchee Refuge recently received $4 million from Congress to fight exotics, Melvin says, and the threat of Old World fern certainly helped loosen up those purse strings for tree triage. "There will be aerial spraying of islands where there aren't any native plants left and follow up with a ground crew on the perimeter," she adds.

Volin, who possesses a bantam build, impressively full goatee, and piercing eyes, is overseeing another ambitious, yearlong project, funded by the water district, to hunt down incipient sporelings of Old Word fern in the east-central part of the Everglades. His research team will visit each of the roughly 500 islands and, using a global positioning satellite device, record each sighting of the fern. The management district will then send out contractors who will find that exact spot and treat the plant with a systemic herbicide that destroys it. It's an endeavor analogous to bicycling across the U.S. to visit every 7-Eleven: They're everywhere, and you never know where the next one will spring up. Just how much this will cost won't be known until later.


On a partly cloudy morning in late May, Volin and three other researchers haul two airboats an hour south of Davie to a public dock along Tamiami Trail. This is the driest month in the Everglades. The water covering the vast expanse of grass surrounding tree islands has slowly dropped through the desiccated winter months, and the routine rainstorms of the tropical season have yet to begin in earnest.

The airboats are relatively small three-seaters, each driven by a cacophonous 12-cylinder aircraft motor. The two boats weave northeasterly for about 20 minutes, sometimes crossing patches of slough that are little but mud. They pull up to a high stand of sawgrass on the east side of a tree island. The real work begins on foot. All dressed in long-sleeved shirts and long pants, they begin the fern hunt by stepping off into water that's just under two feet deep.

This is the first foray into the Glades for Mary Ann Furedi, a new researcher who's only recently moved down from West Virginia, where she walked mountainous terrain studying ginseng. A 20-something with longish, dark-blond hair, Furedi will head this new project, but it will go far beyond the tasks contracted for by the water district. Among other things, they'll be trying to identify "bio-indicators," which are plants or formations that act as hospitable hosts to a particular invasive species. When such a correlation is made, a bio-indicator creates a kind of shortcut for locating invasives and figuring out their reproductive and growing cycles. Melaleuca, for example, is a sucker for spots that have been disturbed by fire.

The sawgrass crackles as the party of scientists bends its way through the serrated blades. A red-tinged bird chatters angrily at the intruders. The ten-foot perimeter of sawgrass gives way to muckier ground with waist-high shrubs. If cave explorers go spelunking, then Everglades surveyors must go spelooshing, because that's the sound of extricating one's foot from the muddy soup.

The interior of the actual island is cordoned off with a thick wall of willows, vines, and holly. The plan is to use a compass and walk a straight east-west line across the island, keeping one eye out for Old World fern and the other on things like a ubiquitous concertina wire-like prickly vine that would as soon decapitate visitors as let them pass through. Furedi and her research team of three or four will spend four or five days a week trekking through tree islands like this.

One bio-indicator for Old World fern appears to be "moss collars." These grow at the base of trees and as high as four feet from the ground. So when the four of them chance upon a decomposing log with a crewcut of green moss on it, they crouch down under the dusky canopy. There are minuscule sporelings there -- the first stage of spore growth. Furedi takes a small plastic container from her backpack and inserts a chunk of moss-laden wood. It's the closest thing they'll see to Old World fern today.

Back in the research lab, Volin will grow the sporelings. He's conducting the same experiment in Australia, using that country's different soils. In the end, he hopes to learn if the soil has some effect on its life cycle.

So far, the news is not good. This is one malleable plant. The fern is something of a sex addict, having evolved as a bisexual that can germinate its spores in any of three ways possible for ferns to do so. The first spore to germinate in a new area is almost always female, researchers found, which then produces a pheromone that turns surrounding spores into males.  

Most ferns are particular about moisture levels during germination; this fern has a more "whatever" attitude. And light? It can grow in dark shadows or at full sunlight atop trees. "This is an incredible plant," Volin enthuses. "The question is: Why is it not invasive in its own native area?" Volin poses. "We don't know that."

In the coming few years, the battle against Old World fern will be mostly waged with conventional weapons: herbicides, pruning shears, and elbow grease. But at the frontline, soldiers know that ultimate victory calls for greater weapons than those.

"The best hope we have is biocontrol," says Melvin, who stands at the edge of the moth-populated tree island. A wall of thick ferns dwarfs her. There's no sign of the fern-eating moths today, but it's a big island, and the tiny insects can't have made much headway yet. Who really knows how well these winged warriors will do in the war against Old World fern?

They're a long way from home, and their enemy is so very well-entrenched. And reproducing fast.


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