FWC seeks input on cattail and torpedo grass management

Posted 1/20/22

The Florida Fish and Wildlife Conservation Commission is seeking input on the management of cattail and torpedograss ...

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FWC seeks input on cattail and torpedo grass management

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The Florida Fish and Wildlife Conservation Commission (FWC) is seeking input on the management of cattail (Typha sp.) and torpedograss (Panicum repens) on Lake Okeechobee. 

Cattail project overview

Several areas in the marshes of Lake Okeechobee have been identified where cattail management would benefit the littoral health of the lake. FWC would like to prioritize up to 800 acres of cattail for management in spring 2022. Herbicide will be applied to cattail in April or May 2022 followed by prescribed fire 3-6 months later. Prescribed fire will open the area up quickly for wildlife use, and it will also consume the dead organic material, so that it does not drop to the bottom of the lake as it decays. Prescribed fire following pre-treatment with selective herbicide extends the efficacy of the herbicide treatments and reduces the amount of herbicide used over time. Cattail management with selective herbicides and prescribed fire is part of an integrated management approach in coordination with other state and federal agencies on Lake Okeechobee.

Potential project areas are:

  1.  First Point and Pleasure Island (Northwest Marsh) – 46.7 and 17.9 acres, respectively. Low water levels in the early 2000s allowed for “scrape” projects, which removed heavy vegetation growth and organic sediment (i.e. muck) in the northwest marsh. These areas have remained cattail-free for almost two decades, and they are often full of dense lily or spikerush stands. Recent encroachment and expansion by dense cattail in these areas makes them a management priority.
  2. Tin House Slough (Northwest Marsh) – 223.5 acres . Adjacent to an area that was managed (herbicide only) in 2020 and a large willow stand that may be used by wading birds and snail kites. It is located directly west of Buckhead Ridge canal. A 200 ft. buffer will be left between the management area and the canal. Treatment of this site will complete management on the south side of the trail.
  3. South Bay (Southern Marsh) – 505 acres. This marsh at the southeastern end of Lake Okeechobee is composed primarily of large cattail stands. Historically, expansive areas of lilies and spikerush were in this area. There have been no recent projects led by FWC staff in this area of the lake. Opening these areas for other native plant species may bring additional wildlife and recreational activity to the area.

Management Techniques:
FWC wants to target 800 acres of cattail using imazamox (Clearcast®; herbicide registered with U.S. Environmental Protection Agency and Florida Department of Agriculture and Consumer Service for aquatic use) and methylated seed oil (MSO; adjuvant labeled for aquatic use). Imazamox will be applied at the recommended label rate of 32 ounces/acre with MSO at 32 ounces/acre at a “12.5-gallon-per-acre” mix rate. At this application rate, imazamox is selective for cattail and will not affect bulrush, spikerush, willow, aquatic grasses (e.g., “Kissimmee grass” and maidencane), lilies, and spatterdock. The Commission Contract Manager will be on-site throughout the treatment process to ensure the contractor is treating within project boundaries and meeting the specifications set forth in the scope of work. FWC will also be monitoring refueling activities. Because of the limited accessibility and large size of some of these management areas, helicopters are the only efficient way to apply herbicide. Approximately 3-6 months after herbicide, prescribed fire will be applied to the management areas.

Benefits of management:
The management, removal, or thinning of dense, monotypic cattail stands can improve native plant diversity, water quality, and recreational opportunities on Lake Okeechobee. The reestablishment of a native and diverse aquatic plant community enhances foraging habitat for birds and spawning and nesting habitat for fish. Cattail management using herbicide and prescribed fire prevents the buildup of organic material, thereby increasing dissolved oxygen levels and water flow within the littoral areas of the lake. Cattail removal can also improve lake access for recreational users (anglers, hunters, wildlife watchers, pleasure boaters, etc.) for many years post-treatment. Previous cattail management efforts led to the largest Everglade snail kite nesting event ever recorded on Lake Okeechobee. Furthermore, documentation shows extensive use of these newly opened areas by wading birds and waterfowl.

Torpedograss project background:

The northwest marsh of Lake Okeechobee is currently dominated by extremely dense monocultures of torpedograss (Panicum repens), which has been classified by the Florida Exotic Pest Plant Council as a Category I invasive wetland species. This prolific grass is outcompeting native wetland plant species and limiting foraging capabilities of fish and wildlife, including the endangered Everglades snail kite. Previous torpedograss management efforts, using large-scale herbicide treatment (broadcast application) followed by small-scale spot management (direct application by airboat or swamp buggy), have greatly reduced torpedograss coverage and promoted growth of native marsh vegetation. To date, over 1,500 acres of torpedograss have been managed and are being maintained.

Management History:
In March 2019, FWC and the South Florida Water Management District (SFWMD) conducted prescription burns on an estimated 3,000-5,000 acres of the interior northwest marsh between Pearce Canal and Indian Prairie canal, which included at least 1,500 acres of torpedograss. In May of 2019, an agricultural
boom/spreader truck was used to broadcast herbicide over 1,140 acres of torpedograss, which included a portion of the prescribed burn area. The torpedograss in this area encompassed almost 100% of total vegetative cover. Post-management monitoring in April 2020 showed 25-50% re-growth of torpedograss throughout the management area. Through a combination of broadcast and spot-treatments, another 1,243 acres of torpedo grass was managed in May 2020. No broadcast treatments were conducted in the 2020-2021 fiscal year. However, spot-treatments were conducted in the two management areas from the previous fiscal years. The second round of spot-treatment reduced torpedograss regrowth to approximately 20%.

Observed management benefits:
In the years following torpedograss treatment, monitoring of management areas in the northwest marsh documented an increase in coverage of native wetland plants, including spikerush, bulrush, cattail, pickerelweed, duck potato, smartweed and marsh lilies. Drier lake conditions and sparser torpedograss coverage resulted in a prolific wildflower bloom in the spring of 2020. Thousands of wading birds, such as ibis, egrets, and spoonbills, were seen foraging in the newly reclaimed marsh habitat, along with dozens of snail kites. In 2021, one of the densest snail kite nesting areas was adjacent to a torpedograss management area. Waterfowl hunters heavily utilized the managed areas in the winter.

Proposed management area:
A total of 1,500 acres of torpedograss will be managed in Spring 2022. The proposed management area is located approximately 100 yards south of the Herbert Hoover Dike and directly northeast of the Indian Prairie Canal levee. The management area will be accessed by the Herbert Hoover Dike (no public access). The new acreage will be located adjacent to the former 1,500-acre management area.

Proposed management methods:
Broadcast application: An agricultural boom truck will be used to broadcast herbicide over 1,500 acres of torpedograss in the Northwest Marsh of Lake Okeechobee. Imazapyr, labeled and approved for aquatic use by the U.S. Environmental Protection Agency (EPA) and the Florida Department of Agriculture and Consumer Services (FDACS), will be applied at the recommended label rate of 64 oz/acre. Imazapyr is a broad-spectrum, systemic herbicide that can effectively eliminate torpedograss. The Commission Contract Manager will be on-site throughout the treatment process to ensure the contractor is meeting the specifications set forth in the scope of work. The truck and boom will be equipped with a GPS that tracks when and where herbicide is sprayed.

Direct application: Airboats or swamp buggies (dependent on water levels) will be used to manage up to 300 acres of torpedograss by “direct application” or “spot treatment”, a precise application of herbicide to control the target species (i.e., torpedograss) and to preserve surrounding desired vegetation. Spot treatments will occur in previously managed areas to control torpedograss regrowth. Although torpedograss will be the only plant species targeted, herbicide application may damage proximal native vegetation. Management via direct application allows for the use of less-selective herbicides, like imazapyr, with reduced risk to non-target vegetation.

Additional management may be conducted as needed if time and funding allow. The Commission Contract Manager will be on-site throughout most of the project to ensure the contractor is meeting the specifications set forth in the scope of work.

Project manager contact information:

Alyssa Jordan
Email: Alyssa.Jordan@myfwc.com
Cell: 863-697-2181

Christy Soldo
Email: Christy.Soldo@myfwc.com
Cell: 863-697-0815

 Comments and concerns regarding preferred management sites, areas of the lake to avoid, management areas to postpone for future years, project size, or project timing are welcome. Please direct comments or inquiries to project managers Alyssa Jordan or Christy Soldo.  

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