Destroying Invaders on the Land and in the Water

Managing District Lands

Aquatic plants

A war is being fought on District-managed lands and water bodies … a war against invasive species potentially invading more than 300,000 acres of publicly owned land and 25 major water bodies.

The invasion of native communities and ecosystems by invasive, non-native species of plant life and wildlife is widely recognized as one of the primary threats to the environmental integrity of Florida’s remaining natural areas.

Invasive species thrive in Florida because the population controls — natural predators and pathogens — found in their native lands are not present in Florida. The invaders often displace native species, disrupt normal ecosystem processes, destabilize community structure and greatly diminish the ability of natural areas to provide suitable habitat for native wildlife.

By now, many Floridians are familiar with the names of these ecological enemies — Brazilian pepper, skunk vine, air potato and cogon grass are some of the better-known invasive species that attack the land; hydrilla, water hyacinth and water lettuce are the most common invaders that infringe upon the waters.

District staff carry out part of the District’s mission of managing the land by controlling the invasive plants that have the ability to spread rapidly and choke out native plant communities.

The Weekiwachee Preserve, located in western Hernando County, is approximately 11,000 acres in size. Brazilian pepper, cogon grass and air potato are the three main invasive plants that crop up in the preserve. Approximately ten years ago, Brazilian pepper was abundant throughout the preserve. Now this unwelcome species is difficult to find. Invasive species on the preserve are under maintenance control, which means that all known infestations have been controlled and staff periodically goes out to look for and treat new infestations.

Most new parcels of land purchased to become part of the preserve have pepper or other invasive species and need to be treated. Kenny Smith, vegetation management crew leader, recently inspected such an area wearing a backpack sprayer. Smith pinpointed the invasive plants, Brazilian pepper in this case, and treated them.

Brian Nelson, aquatic plant manager, explained why the peppers here are being treated with herbicide instead of being mechanically cleared. “In the Weekiwachee Preserve, we currently have mostly native plants with a few peppers here and there,” said Nelson. “You couldn’t go in with the heavy equipment because it would tear everything up. Disturbing the land would lead to more infestation by aggressive invasive plants because they like disturbed soil.”

“Mechanical clearing of invasive species is a technique used primarily to remove large, dense stands of invasive plants,” said Nelson.

These infestations, often consisting of only one species, are known as monotypic populations. There are typically few, if any, beneficial native plants left in these areas to be damaged by heavy equipment. Projects that begin with the mechanical removal of invasive species populations often include some earth moving to restore or create wetlands and the replanting of native species populations as part of a comprehensive restoration plan. A good example would be the Surface Water Improvement and Management (SWIM) Program project at Cockroach Bay in southwest Hillsborough County.

Another success story is the recently acquired Deer Prairie Slough property in Sarasota County, which harbored expanding infestations of the well-known melaleuca tree. The District has controlled all known infestations of melaleuca on the property.

Besides fighting the well-known invaders, District employees are always on alert for new invasive plants threatening our conservation lands. For instance, a plant known as Old World climbing fern is beginning to spread into central Florida. The fern was first discovered in Martin County and is spreading north. This aggressive, non-native fern is being controlled on six District-owned properties. Old World climbing fern has a vinelike growth form that gives it the ability to blanket trees, shrubs and other plants, smothering the whole community of plants. It also alters natural fire ecology by carrying fire into the tops of trees and into plant communities that cannot tolerate fire, such as cypress domes and river swamps. The District is concerned about preventing the spread of Old World climbing fern into the Green Swamp.

The management of troublesome aquatic plants is a cooperative effort between the District and the Florida Department of Environmental Protection.

Water hyacinth, water lettuce and hydrilla are the three main invasive species that staff control on District-managed waters. If these rapidly spreading aquatic plants are not controlled, recreational activities, navigation, flood control, water quality and fish and wildlife habitat populations can be negatively impacted.

Aquatic management crews recently treated hydrilla on the Rainbow River in Marion County and water lettuce on Jumper Creek in Sumter County. Both flow into the Withlacoochee River.

Hydrilla is an invasive submerged plant species from southeast Asia that was introduced to Florida in the late 1950s. Because of its rapid expansion and choking growth form, the state spends approximately $18 million each year to remove hydrilla from public water bodies.

Water lettuce is a troublesome floating aquatic plant from South America that was first reported in Florida in 1765. Water lettuce is considered one of the worst weeds in the subtropical and tropical regions of the world.

While the District’s aquatic plant management crews treat invasive plants all year round, Grady Vance, aquatic plant management supervisor, says the winter is their time to catch up because the invaders do not grow as fast.

“We also go great guns in the summer growing season,” said Vance. “That’s when water lettuce and water hyacinth can double their population in less than three weeks!”

Crews use Reward®, an aquatic herbicide, to treat water lettuce. Treatment areas are posted with warning signs displaying treatment dates and applicable water-use restrictions. Restrictions on water treated with Reward include no livestock watering for one day, no irrigation of crops for five days and treated water should not be used for drinking for two days. Restrictions do not apply to tap or well water.

Native aquatic plants occasionally cause problems as well. A good example would include floating tussocks and pennywort. Tussocks are like floating islands and can be made up of a variety of plants. They are formed when rooted plants pop up from the bottom carrying sediment with them. Tussocks typically form during drought periods when lowered water levels allow emergent plant populations to expand. When the water levels return to normal, the plant, roots and dirt clump float to the top.

Other than causing localized problems in small access canals, native aquatic species like pennywort usually do not cause significant problems and are rarely targeted for control.

To learn more about the District’s invasive species control programs, please visit the aquatic plant management section under the Projects & Programs page on the District’s web site at