Story and Photos by Alex Perret
Each year, as temperatures rise and the general appearance of the Louisiana landscape progresses from brown to green, many residents take notice that their local waterways appear to shrink. In this case we’re not talking about evaporation and lower water levels from the heat, but rather the rapid growth of aquatic vegetation that plagues many of the state’s waterbodies. Every summer, Louisiana’s public waters are covered with over 300,000 acres of nuisance aquatic weeds, including water hyacinth, giant and common salvinia, hydrilla, and alligator weed. Of course, Mother Nature is often a defining factor of how bad the plant growth will get in a given year. Multiple hard freezes during the winter months can go a long way in reducing the amount of aquatic vegetation that is present the following summer. On the other hand, a mild winter can mean an abundance of plants obstructing popular recreational areas in many waterbodies across the state.
The Louisiana Department of Wildlife and Fisheries (LDWF) is tasked with providing access to Louisiana’s public waters. The LDWF Aquatic Plant Control Program (APCP) treats approximately 60,000 acres of aquatic weeds each year in an effort to keep major public waterways open for passage and recreation. All available resources are used in conjunction to effectively control this amount of vegetation.
The APCP includes 22 spray crews located in nine districts across the state. These crews are responsible for routine herbicide applications in areas of public waterways that have chronic aquatic weed issues. They typically apply herbicides from surface drive boats, mudboats and skiffs, but occasionally use pirogues, ATVs, trailer mounted sprayers and backpack sprayers to treat shallow and forested areas. In situations where there is a large amount of vegetation in one area, or in shallow areas, private herbicide applicators are often used because of their ability to provide multiple airboat spray vessels at the same time. This allows LDWF spray crews to continue with scheduled routine treatments while the contract sprayers treat large, isolated areas of infestation. Aerial applications from helicopter-mounted equipment are also used in situations with large expanses of vegetation and few trees.
METHODS OF CONTROL
Aquatic plant control is usually accomplished with one of three different approaches. Chemical control involves application of herbicides approved by the EPA for use in aquatic environments. These herbicides go through years of rigorous testing to ensure safety to the public and the fisheries when used properly. Different herbicides are used for certain plants and are generally sprayed on floating vegetation and injected into waters containing submerged growth. Mechanical control involves physically altering or removing the plant material with harvesters, cutters, rakes, and also with water level fluctuation. Biological control is accomplished by releasing organisms whose feeding habits and life cycle inhibit the growth of certain invasive plants. Examples include grass carp for submerged vegetation, alligator weed flea beetles, and giant salvinia weevils.
INTEGRATED PLANT MANAGEMENT
With increasing plant control demands and a limited budget, LDWF has instituted a management scheme that incorporates all three approaches to aquatic weed management. In an effort to work smarter and provide more long term control, the APCP has placed an emphasis on using control methods such as drawdowns, grass carp stocking, and weevil releases along with herbicide applications. Integrated Plant Management (IPM) allows the APCP to work more efficiently and effectively, and allows for more acres to be treated without an increase in expenses. This IPM approach has been beneficial in allowing LDWF the resources to step in and treat aquatic vegetation in areas that had previously been controlled by the U.S. Army Corps of Engineers (USACE). The USACE Removal of Aquatic Growth Program lost its funding beginning in 2012, leaving LDWF with 30,000 acres of additional plant control responsibility. The successful use of IPM in lakes across the state has allowed LDWF the ability to initiate spray efforts in these former USACE controlled areas.
The IPM approach has allowed LDWF to effectively control some of the aquatic vegetation problems in Louisiana. As a result of the program, residents currently have access to some public waters that were not useable in the past because of excessive plant growth. One example of this success can be found in the fight against giant salvinia in Lake Bistineau in northwest Louisiana. In 2009, nearly 50 percent of the 17,000 acre impoundment was covered with this invasive aquatic weed, and much of the lake was unusable for recreational purposes. A drawdown was initiated that fall and water levels were dropped to 7 feet below pool stage. This dewatering stranded a large amount of giant salvinia that was located in shallow, densely forested areas of the lake that were inaccessible. Several hard freezes that winter also helped to reduce the amount of giant salvinia in the lake. Only the main channels of the lake contained water during much of 2010, and plants found in those areas were treated with herbicides.
During 2011, LDWF crews continued to respond to notifications of giant salvinia growth throughout the lake. At the same time, private spray contractors were used to treat large expanses of alligator weed that were limiting access. Currently, LDWF crews are applying herbicide to scattered giant salvinia found on the southern end of the lake while contract sprayers are being used to treat areas of coverage greater than 300 acres. Giant salvinia weevils have been stocked several times in areas with limited access, and a drawdown will be used if the lake contains greater than 1,600 acres of surface plant coverage. Presently, there are approximately 500 acres of giant salvinia coverage, most of which is in the forested and inaccessible northern portion of the lake. With the onset of warmer temperatures recently, local residents and members of the community have been able to enjoy their lake that was virtually unusable just a few years ago.
Aquatic plant coverage at Lake Bistineau has declined swiftly through more efficient use of available control methods. Other plant control successes as a result of this approach are also evident at Turkey Creek Lake and Toledo Bend Reservoir, as well as throughout the coastal marshes where weevils and herbicide applications have been successful at reducing giant salvinia populations. The hope of LDWF is to continue to find the most efficient management scheme for all of its waterbodies and to utilize all of the tools available to provide clean, healthy waterways for public enjoyment.