Invasive Plant Management on Lake Istokpoga Fish Management Area


            Management of cattail, pickerelweed, and other invasive aquatic plants is part of the Florida Fish and Wildlife Conservation Commission’s (FFWCC) Aquatic Habitat Enhancement Program for Lake Istokpoga.  Lack of adequate fluctuation, reversal of the natural fluctuation cycle, and low water levels during the prime growing season for aquatic plants have encouraged expansion of cattail, pickerelweed, and other invasive plants in Lake Istokpoga since 1962.  Bands of dense cattail and pickerelweed encourage the development and expansion of tussocks and tussock precursors (water primrose, burhead sedge, water hyacinth, water lettuce, etc.) by reducing wind and water movement throughout littoral areas.  Lack of water movement limits flushing of detritus on which tussocks may form.  Cattail, pickerelweed and other tussock precursors not only displace more desirable aquatic vegetation communities, but also deposit organic debris on the lake bottom.  Loss of native littoral plants and sandy benthic substrates reduces areas for fish spawning, forage and juvenile fish habitat, waterfowl feeding, public access, and navigation on Lake Istokpoga.  Although some animals exploit cattail and tussock precursors for nesting and protective areas, the overall ecological and economic impacts to the lake are strongly negative.

            FFWCC’s Aquatic Habitat Enhancement Program is broken into three components with the primary goal of the program being enhancement and management of Istokpoga’s aquatic habitat for the long-term benefit of fish and wildlife and the people who utilize those resources.  The three program components include:

a)      mechanical removal or consolidation of tussock and associated organic sediments;

b)      establishment of native aquatic plant species through natural recolonization or revegetation with desirable native aquatic plant species;

c)      management of future tussock formation through control of invasive aquatic plants with herbicides and aquatic harvesting.

             In Spring 2001, the FFWCC conducted an aquatic habitat enhancement drawdown on Istokpoga, in which 1,308 acres over 21 miles of shoreline were scraped of tussock and organic material.  These enhanced areas provide sandy substrate on which native desirable plants are encouraged to grow.  However, pickerelweed, as the primary aquatic plant invader in these sites, becomes dominant and creates monoculture stands, which begin to exclude other desirable plants.  Also, since 1998, the FFWCC has maintained a seasonal aquatic harvester program around Big Island, Bumblebee Island, and Henderson’s Cove to control tussock expansion and reestablish productive littoral habitat.  This program is limited, however, by water depths at the machinery can effectively operate and high program costs (>$4,000 per acre).   An aquatic plant management program, which includes herbicide management of invasive plants and revegetation with desirable native species, is necessary to provide more diverse habitat, which is better utilized by fish and wildlife.

            Invasive aquatic plants are controlled with aquatic herbicides to encourage recruitment of desirable plants and increase the diversity of aquatic plants throughout the lake.  Invasive species targeted include, but are not limited to, dense pickerelweed, dense cattail, burhead sedge, water primrose, water hyacinth, and water-lettuce.  A long-term maintenance program has been implemented in coordination with the Highlands County Aquatic Weed Control Project and Florida Department of Environmental Protection’s Bureau of Invasive Plant Management to maintain desirable vegetation communities and prevent formation of tussocks.  As part of FFWCC’s aquatic plant management program, dense stands of cattail, pickerelweed, and other tussock precursors are managed with herbicides by helicopter or airboat (less than half of the cattail and pickerelweed is actually treated within the treatment areas) to leave bands of sparse cattail and pickerelweed, which are better utilized by fish and many wildlife species.  Areas of dense vegetation are left available for use by waterfowl, wading birds, and other wildlife as roosting and protective habitat.  Bulrush (buggy-whips), knotgrass (Kissimmee grass), and other desirable native vegetation will not be sprayed.  The herbicides to be used are glyphosate (tradenames: AQUANEAT or RODEO) and 2,4-D Amine (tradename = WEEDAR 64), which are the same chemicals many homeowners use to treat weeds in their yards.

             The Florida Fish and Wildlife Conservation Commission's Division of Freshwater Fisheries has selected a total of 1,024 acres of dense vegetation for herbicide treatment as part of the Lake Istokpoga Fish Management Area (FMA) aquatic habitat enhancement program.  Areas to be treated by airboat range along the shoreline from Highlands Park Estates to Istokpoga Canal.  Areas to be treated by helicopter include Big Island marsh, Bumblebee Island marsh, and Grassy Island, areas within Henderson’s Cove, and south of Istokpoga Canal.  Depending on weather conditions, the airboat treatment is scheduled to begin on October 6 (Monday) through October 30 (Thursday).  The helicopter treatment is scheduled to begin on October 27 (Monday) and continue through October 30 (Thursday).  Maps showing treatment areas will be posted at Istokpoga's public boat ramps and local fish camps.  Please try to avoid these areas during the spray operations.  For additional information, contact Beacham Furse or Larry Davis at (863) 462-5190.