Florida Battles Invasive Melaleuca Acre By Acre

FORT LAUDERDALE, Florida, November 2, 2004 (ENS) - Melaleuca is an exotic invasive tree that was introduced into South Florida from Australia in the late 19th century. Used extensively as an ornamental plant and as a soil stabilizer in swampy areas near lakes and canals, no one guessed that it would one day displace native plants and animals, draw up water from wetlands, and create a fire hazard.

Now, more than a century later, Melaleuca quinquenervia, also called punk tree, paperbark tree, or cajeput, is seen as one of the Florida Everglades ecosystem's worst enemies. It causes as much as $168 million in environmental losses every year and takes over 14 to 15 acres a day.


Aerial herbicide is used by land management agencies to control melaleuca trees on large, remote areas of the Everglades. If not controlled, the melaleuca trees in the foreground will soon invade the sawgrass area in the background, which is the way the Everglades looks before melaleuca invasion. (Photo Stephen Ausmus courtesy USDA)
During the dry season in South Florida, huge forest fires, aggravated by the high oil content of melaleuca leaves, scorch thousands of acres of natural areas and encroach on developed ones, endangering lives, homes, and businesses.

A collaborative effort to wipe out the melaleuca, called the TAME Melaleuca Project, is being carried out by the USDA's Agricultural Research Service, the University of Florida's Institute of Food and Agricultural Sciences, and the South Florida Water Management District.

In 1990, the South Florida Water Management District began an aggressive campaign to lower melaleuca populations across South Florida. As a result, melaleuca acreage on public lands has decreased dramatically. But the 60 to 100 foot tall trees continue to spread at such a high rate on private property that there has been little decrease in overall acreage covered.

"That's because controlling melaleuca is tricky," says Cressida Silvers, an entomologist with the Agricultural Research Service Invasive Plant Research Laboratory in Fort Lauderdale. "The high volume of seeds held in the tree's canopy helps this species to disperse and establish."


Stress on the trees causes them to open their capsules and release the seeds. Mature trees can hold millions of seeds. (Photo courtesy TAME Melaleuca)
Any stress to the trees, such as fire, cutting, or spraying, causes millions of little seeds to fall from the canopy and quickly germinate. This creates what looks like "a carpet of tiny seedlings," Silvers says.

Traditional controls, such as spraying the trees with herbicide or cutting them down and applying herbicide to the remaining stumps, have had some effect, but a comprehensive approach is needed to increase the long-term effectiveness of management efforts.

Any discussion of melaleuca management should stress the concept of Integrated Pest Management (IPM), says Silvers. IPM integrates various control methods, and for melaleuca these are principally mechanical, chemical, and biological control agents. All three are needed to successfully control melaleuca, and any one method will not control trees.

While herbicides will kill trees, they cannot keep up with seed production, Silvers explains. "Biological control agents decrease seed production and growth rates, but don't usually kill trees. Unless a stump is ground, trees will resprout after being cut down. Thus, a combination of all tactics is the only way we will ever win the war on melaleuca."


The melaleuca leaf weevil was imported from Australia, the melaleuca tree's native land. (Photo courtesy USDA)
Three insects are used against the pesky tree. The first biological control agent, the melaleuca leaf weevil, Oxyops vitiosa, from Australia was released in 1997. More than 8,000 weevils were distributed at 13 melaleuca-infested locations in South Florida. Today, millions of the quarter-inch-long weevils are eating the young leaves of melaleuca trees.

ARS scientists and colleagues have found great success with the second biological control agent, the aphid-like psyllid Boreioglycaspis melaleucae. This tiny insect is another natural enemy of melaleuca from Australia, and both adults and young psyllids feed on the tree's sap.

Insect number three is the melaleuca bud gall fly, Fergusonina turneri. The female gall fly lays her eggs in young buds, causing the plant to form galls.

But herbicide and mechanical methods are still needed. Herbicide is sprayed from aircraft over large areas where melaleuca is dense or hard to reach by other means. Aerial applications kill standing melaleuca, but after the treated trees release their seeds, the emerging seedlings require treatment. Because biocontrol insects are self-perpetuating, they are an ideal tool for locations that are difficult to reach.


From boat ramps, workers take airboats around the Everglades. They disembark and walk from tree to tree killing as they go. (Photo courtesy TAME Melaleuca)
The brontosaurus is also used in the attack. This monster of a machine that chips a standing tree from the top down to the ground using a grinder attached to the machine's head. All that's left of the once-gigantic tree is mulch that contains melaleuca seedlings, which may soon sprout. But biological control then attacks the new growth.

The feller buncher is a smaller machine, with pinchers and a saw at the end. It saws off the tree at the trunk, applies herbicide to the stump, takes multiple trees at a time with its pinchers, carriers them like a flower bunch, and stacks them in piles. Piling up the melaleuca trees limits the area where seeds will fall, making the inevitable carpet of seedlings smaller and more manageable.

TAME Melaleuca has set up nine demonstration sites around South Florida that range from small, less than10 acres, to large,greater than 100 acres. The Everglades Buffer Strip at Holiday Park in Fort Lauderdale, for example, is nearly 105 acres of dense melaleuca and other invasive plants, such as Australian pine and Brazilian pepper, located along U.S. Highway 27 in Broward County.

Here, four separate plots each received a different herbicide or mix of herbicides. The dead trees were stacked to reduce the amount of acreage where the seeds would fall.


Melaleuca trees invading islands in the Loxahatchee National Wildlife Refuge in Palm Beach County. (Photo courtesy TAME Melaleuca)
Machines do their noisy best on 15 acres and some of the stumps are treated with herbicides. And the team released melaleuca psyllids on 10 acres where weevils are also present from earlier releases.

Still, the trees are difficult to eradicate.

Melaleuca is regulated by the state of Florida and the federal government as a noxious weed. Melaleuca trees may also be locally regulated, as they are in Palm Beach and Lee Counties.

There are few beneficial uses of the melaleuca quinquenervia. It has few commercial uses but could be used for cellulose or as a fuel. As a nectar and pollen source it is important to the beekeeping industry.

Melaleuca appears to be a respiratory irritant when found close to human habitations and seems to repel mosquitos.