Cooperative Extension Service 
Institute of Food and Agricultural Sciences
Hendry County Extension P. O. Box 68 LaBelle, Florida 33975-0068 Phone (863) 674-4092

Hendry County Horticulture News

Innocent Looking Fern Is A Real Threat

The uncontrolled expansion of an dainty, attractive, innocent looking exotic fern is threatening to become one of Florida's most serious ecological threats, rivaling such other invasive species as the Brazilian pepper as a despoiler of our native ecosystems.  The Old World climbing fern - Lygodium microphyllum has been variously described as biological pollution of the worst kind, the "kudzu" of the Glades and south Florida's next big weed problem that will replace the maleleuca as a species of special concern over the next few years.

Just like kudzu which has laid waste to vast areas of the southeastern United States, the Old World climbing fern covers trees, shrubs and other vegetation with picturesque cascades of vines that eventually shade out and smother everything in it's path.

Like many other invasive exotic plants, this imported pest grows quickly on a wide range of soils and environmental conditions, propagates easily, resists native pests, and has no natural enemies to keep it in check.  Without a doubt, the Old World climbing fern is bad news.  This foreign pest can rapidly invade undisturbed habitats crowding out native plants, destroying habitats and food sources for native animals.

It's ability to grow quickly and produce a great deal of potential fuel in a short period of time greatly increases the risk of fire hazard in natural areas.  The dense mats of vegetation up to several feet thick produced by the climbing fern allow fires to burn hotter increasing their destructive potential.  Scrambling up and over anything with freely branching fronds or leaves, it's rampant growth can act as a bridge, carrying fire high into the forest canopy causing the death of normally resistant species such as pine and cypress.  This so-called "fire ladder" allows wildfires access to normally protected areas such as hammocks and cypress heads.

Old World climbing fern is a fern with climbing fronds.  What looks like a vining stem is actually a climbing, freely branching, leaf, which can be up to one hundred feet long.  The leaflets branching off the main stem are 2-5 inches long.  Old World climbing fern has two types of leaflets on its climbing leaf.  Those with a simple unlobed outline are vegetative leaflets.  The more convoluted leaflet is a reproductive leaflet, which produce spores leading to the development of gametophytes. Gametophytes are separate small plants that produce sexual cells, which unite to form an embryo and ultimately a new climbing fern.  The reproductive plants or gametophytes are very small, and rarely noticed.

This alternating of vegetative and reproductive plants as separate generations is typical of most ferns.  The ability of the climbing fern to produce of wind borne spores, that may be carried thirty to forty miles by prevailing winds, makes it hard to contain and contributes to its explosive potential to spread rapidly to new areas.

The Old World climbing fern, which is native to Asia and Australia, is a relative newcomer to Florida.  It was introduced in the 50's, into Palm Beach County, by the ornamental trade which thought that it might find potential use in hanging baskets.  Although it spread slowly at first, by the early 90's it had infested tens of thousands of acres on the east coast of Florida.  By the mid 90's, it had spread to the west coast and was established widely from Sarasota to Naples.  Old World climbing fern presently covers an estimated thirty five thousand acres of land and has the potential to double in extent annually.  Positive identification of Lygodium has recently been confirmed locally with sizable populations present in places such as Alva, LaBelle, and Muse.

Fortunately, climbing fern is relatively easy to kill.  Small patches may be pulled out by the root and the site monitored for new sprouts.  Sprouts can be hand pulled or treated with herbicides.  For larger areas, remove as much as the fern as is possible from trees and other vegetation and then treat the remaining plant with an herbicide.  Contact the Hendry County Extension Office for recommended herbicides for Lygodium and other invasive plants.  Several treatments may be necessary to eradicate this pest.  Note that many herbicides are not selective and will injure desirable plants if not applied cautiously.  Careful disposal of climbing fern is critical as dried fern may spread viable spores to new areas.  Small amounts should be bagged to contain spores.

A number of institutions and agencies, including the University of Florida, are currently studying ways to combat this pest.  Education and raising the level of awareness of the problem among the public and government officials will help pave the way for further action.  Stronger legislation to restrict the introduction of new species and funding for programs to control established invasive plants is desperately needed to protect Florida's native flora and fauna from being totally overrun by alien species.  You can help immediately by learning to recognize this and other invasive plants and eliminating them on your property.  Good luck and good gardening.

Gene McAvoy is the horticulture agent with the Hendry County Extension Service.  Direct your horticulture questions to PO Box 68, LaBelle, FL 33975,  e-mail - or phone 863-674-4092 or  863-983-1598.  You are also welcome to visit the Hendry County Extension Office at 225 Pratt Blvd., LaBelle.   Office hours are from 8:00 - 5:00.

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