New TAME Melaleuca project attacks invasive tree in South Florida

July 21, 2004

FORT LAUDERDALE, Fla. — In Florida, where invasive plants account for as much as 31 percent of all plant species, state and federal officials are ratcheting up their fight against the melaleuca tree, one of the most significant threats to the stability of the Everglades ecosystem.

The new TAME Melaleuca project, short for The Area-wide Management and Evaluation of Melaleuca, was recently established by the U.S. Department of Agriculture in cooperation with the University of Florida and the South Florida Water Management District.

Control measures for the troublesome tree will be demonstrated for residents and other land managers at eight South Florida sites in Broward, Collier, Hendry, Lee and Palm Beach counties.

“The good news is that various government agencies have been able to clear melaleuca from almost 100,000 acres of publicly owned natural areas, such as Big Cypress National Preserve, the Lake Okeechobee marsh and the Florida Everglades,” said Ken Langeland, a professor of agronomy with UF’s Institute of Food and Agricultural Sciences.

“The bad news is that the tree is still spreading rapidly on privately held lands where there are no controls – resulting in a no-net loss of melaleuca. Dense forests of melaleuca now occur mainly on private lands in Broward, Miami-Dade, Palm Beach, Lee, Martin and Collier counties,” he said.

Langeland, a specialist on aquatic and invasive plants, said the tree invades moist, open habitats, forming dense, often impenetrable stands of trees. Native wildlife is threatened because the tree crowds out beneficial native plants. It’s also a serious fire hazard, because oils in the leaves burn hot and are difficult to extinguish.

“Imported from Australia in the 1880s as an ornamental plant that would help dry up useless swamps, melaleuca has behaved badly – invading a wide variety of natural landscapes in South Florida,” he said. “Everything from wetland marshes and prairies to cypress domes and pine flatwoods is affected, and one mature tree can hold as many as 50 million seeds.”

By the early 1900s, only 50 years after it was introduced, melaleuca had spread over hundreds of thousands of acres. In 1967, it was found in Everglades National Park, and by 1993 it covered 488,000 acres in South Florida. Melaleuca is now listed by federal and state agencies as a noxious weed, making it illegal to possess, sell, cultivate or transport in Florida.

Langeland, who is chairman of the technology transfer team for the TAME Melaleuca project, said an integrated pest management approach is being used to control the tree.

“Combining different management control options will be more effective than any one method alone,” Langeland said. “The goal is to stop new infestations and treat existing infestations before they spread and become even more difficult to control.”

Aerial spraying of herbicide is effective for large stands of melaleuca, he said. Ground crews are used to girdle trees and apply herbicide to individual trees. Cutting melaleuca trees will not kill the stumps or the roots, so an herbicide must be applied to the cut surfaces to prevent re-growth. Flooding doesn’t kill mature trees. And while fire may destroy seedlings and saplings, it won’t kill mature trees, and actually helps release and spread the seeds. Heavy equipment, which is difficult to use in remote areas with dense melaleuca, may harm soils and native plants, but it is useful in certain situations, he said.

A long-term management option is biological control, Langeland said. Biocontrol involves the importation of agents, such as host-specific insects, to naturally control invasive species such as melaleuca. After 16 years of research, five biocontrol insects have been imported from Australia, and two have been released in South Florida by USDA and UF researchers.

“We have been seeking effective biological control agents for melaleuca since 1986,” said Paul Pratt, TAME Melaleuca project leader at the USDA Invasive Plant Research Laboratory located at UF’s Fort Lauderdale Research and Education Center. Pratt also is a UF courtesy assistant professor at the center.

“Since melaleuca trees are native to Australia, we searched for and found two natural enemies of melaleuca in that country,” he said. “Both insects were released after an extensive quarantine period and careful testing to make sure they will not become a problem in South Florida’s fragile environment. Neither biocontrol insect is a threat to people, animals or other plants.”

In 1997, the melaleuca weevil, or Oxyops vitiosa, was released to control melaleuca by feeding on leaves. By the end of 2002, the weevil was established in 12 South Florida counties, reducing seed production by about 80 percent on trees they attack. In 2002, the melaleuca psyllid, or Boreioglycaspis melaleucae, was released. About the size of a gnat or small ant, the psyllid feeds on melaleuca’s clear sap, severely damaging seedlings.

“Unlike the weevil, which is restricted to dry habitats, the melaleuca psyllid can become established in any melaleuca-infested area,” Pratt said. “We expect this will provide more effective control of the tree.”

Other scientists working on the TAME Melaleuca project include Cressida Silvers, a USDA entomologist and project manager; Jim Cuda, an assistant professor in the UF entomology and nematology department; Alan Hodges, an associate in the UF food and resource economics department; and William Overholt, an assistant professor of entomology at the UF Indian River Research and Education Center in Fort Pierce.

For more information on the TAME Melaleuca project, visit tame.ifas.ufl.edu.