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

Alien Invaders Threaten Florida's Ecosystems

Florida's terrestrial and aquatic ecosystems are being invaded "aliens."   These "aliens" are not green, bug-eyed creatures from "outer space" but rather a host of non-indigenous, unwanted plants, animals,  insects, and diseases from exotic places around the globe.  Because these nonnative did not co-evolve with native species already in the ecosystem, they can have profound effects.  Native species often have no resistance to the ravages of exotic insects and diseases and are unable to compete successfully with alien species.  Having no natural enemies, these invasive exotics are often difficult to control.

Insect pests and diseases, such as the medfly and citrus canker threaten Florida's multi-billion dollar agricultural sector and have cost the state millions of dollars in eradication efforts.  Many other insects and diseases, including the fire ant, Caribbean fruit fly, and tomato yellow leaf curl virus have become established in Florida.  Most have resulted in serious economic loss. A number of fish and reptile species have also invaded the state and have resulted in the dramatic reduction of native species.  When is the last time that you have seen a little green tree frog or the bright green anole lizard ("Florida chameleon")?  Both species, which were once very common, have been pushed aside by foreign invaders.

One of the most severe environmental problems facing our natural areas is the explosive spread of invasive exotic pest plants. These organisms invade and rapidly spread in natural areas with harmful consequences. During 1993, 456 million exotic plants were imported into the United States; about 80% entered through the Port of Miami. Some of these plants are potential invaders and they can harbor, along with other cargo and the ships that transport them, other invaders, including diseases, insects, and other animal life. Some exotics cannot survive in the new environment, while others continue to exist only with human help. Additional exotic species escape and survive in natural and distressed areas.

Florida is particularly vulnerable to exotic invasion because of its subtropical climate, the disturbance of large parts of its landscape, and its geographic shape. There are currently more than 1,300 exotic plants in the state, making Florida one of the states with the most severe exotic pest plant problem in the country. Approximately 1.5 million acres have been invaded by exotic pest plants in Florida. About 45% of the invading plants were originally imported for ornamental landscape use and many are still commercially available.

Many of these invasive species spread rapidly and form dense populations, primarily by out competing native species due to a lack of natural controls. The competitive advantage held by these exotics is usually the result of their location in hospitable environments where the normal natural controls of disease and natural enemies are missing. As exotic species expand, they can disrupt the ecosystem. A few of the worst invaders and the extent of their infestation are: Brazilian pepper (703,504 acres),  maleleuca (488,824 acres), Australian pine (373,723 acres), hydrilla (75,500 acres) and the climbing fern (25,781 acres). Other well known exotics that are invading and disrupting plant communities include: asparagus fern, earleaf acacia, air potato, lantana, carrotwood, Surinam cherry, and wandering jew to name a few.  These and over 60 other invasive exotics are listed by the Florida Exotic Pest Plant Council as Category 1 species that have become or have the potential to become serious pest problems in the near future.

Few methods exist to effectively combat the advance of these pest plants. Chemical herbicides and mechanical removal  are most effective during the initial stage of invasion, when the area affected is small and eradication is possible. Chemical and mechanical methods lose effectiveness as the affected area expands. This loss of effectiveness results from loss of direct access to affected areas and seed sources, concern for environmental impacts of the control methods, and from the high costs of chemicals and implementation. After an invasive species spreads, additional measures must be employed if control is to be accomplished. Biological control or bio-control, which involves the use of host-specific natural enemies from the exotic pest's native area, can reduce the invaders' competitive advantage.  Until a biological control system is developed, every available control method must be used.

The problem of invasive exotic pests is large and growing. A multi-pronged strategy is needed to control the situation. Introduction of new pests must be regulated and the continued sale of those already here should be stopped. Once a new pest is identified, quick action to eradicate the invasion must be taken. More effective weapons to control existing pests, especially bio-control, must be developed.  Some counties and municipalities have enacted legislation banning the planting and sale of some of these exotic invaders.

Home owners can to educate themselves about potential plant pests.  On your property, remove all invasive non natives and avoid planting these exotics on your property. Your stewardship can help make a difference in stemming this tide of invaders that threatens our quality of life.  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.

The Institute of Food and Agricultural Sciences is an Equal Employment Opportunity - Affirmative Action Employer authorized to provide research, educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap or national origin.

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