Invasive Plant Species Control
Some of the invasive exotic plants known to occur in the wetland habitats on the refuge include alligatorweed ( Alternanthera philoxeroides), parrotfeather ( Myriophyllum aquaticum), purple loosestrife ( Lythrum salicaria), Paspalum spp., and Sesbania spp. Currently, only a few species are creating significant problems on the refuge, but the potential exists for others to become major problems. Control of these species can be extremely difficult. In many cases, control will only be temporary due to the extremely invasive nature of these pests. Even if species are controlled on the refuge, they can easily be re-introduced from adjacent river system during flood events. The refuge staff has not conducted a complete inventory of all known species and their locations within the refuge boundaries. Monitoring has been limited to the intensively managed wetland habitats.
The invasive nature, adaptability to various soil moisture conditions, and resistance to mechanical and chemical control of alligatorweed have resulted in a significant impact on wetland management activities within the impoundments in Duck River Bottoms. Alligatorweed was first documented in the Duck River Bottoms in 1988 with a total of four acres found within four separate impoundment nuts. Currently, it is impacting about 400 acres within the bottoms. Alligatorweed also occurs in small patches within Busseltown Bottoms. Several locations of heavy and light infestations occur on Kentucky Lake, both on and off the refuge. Most of the refuge’s invasive exotic plant monitoring and control efforts are focused on this plant within the impoundments on the Duck River and Busseltown units. Control efforts began in 1989 and continue to this date. Experiments have been conducted to evaluate mechanical (disking), water level management (keeping it as dry as possible), and herbicide (several different chemicals) treatments. Mechanical control efforts have been ruled out since disking spreads the plant, due to its ability to sprout from cuttings. Dry conditions do stress alligatorweed and allow competition from other plants, but will not eliminate it and the resulting habitat conditions are poor waterfowl habitat. Most locations where alligatorweed thrives cannot be dried sufficiently to have long-term effects. Frequent herbicide treatments appear to be the only means to gain any control over this plant. Of the herbicides tested, aquatic labeled imazapyr (i.e. Habitat) seems to produce the best results. Applications of Habitat have been done using ground equipment such as backpack sprayers, tractors and ATV mounted boom sprayers and aerially by helicopter. When possible, aerial treatments are the most feasible, due to access issues and the amount of area covered relative to the effort applied. Aerial treatments of began in 2002 with 320 acres treated. In recent years an average of 150 acres are treated annually. The preliminary result of this intensive effort seem to be reducing the density of alligatorweed but not eliminating the threat of reestablishment if control efforts are relaxed.
Parrotfeather, though known to be extremely invasive in aquatic environments, has only been documented to occupy two acres within two impoundments in the Duck River Bottoms. This plant was first found in small patches within one of the impoundments in 2002. Parrotfeather was first treated with 2,4-D in 2003, which did not prove to be very effective. A broadleaf herbicide, Renovate (aquatic labeled Garlon), was tested in 2004, however Habitat has proved to be the most effective control. Hopes are to eliminate this plant before it becomes well established.
A small colony of purple loosestrife exists on the Busseltown Unit. This colony has been present there for a number of years with little indication of expansion. Herbicide treatment with glyphosate has been attempted for several years prior to 2003. This practice may have reduced the expansion of the colony but appeared to have no other long-term impacts. Beginning in 2003, a biological control agent was released in the purple loosestrife colony. Approximately 2,500 Galerucella beetles were released with an additional 2,500 Galerucella beetles released each year since. A slow decline of this colony has been noted, however, results of this treatment have yet to be determined.
Paspalum spp. and Sesbania spp. are present in isolated patches within some of the moist-soil areas in Duck River and Busseltown bottoms. They have not currently reached unmanageable levels, but do impact moist-soil production where they occur. The refuge has applied some efforts towards controlling these plants, but with the focus on alligatorweed this effort has been limited. Where practicable , Paspalum spp. can be controlled by prolonged deep flooding during the growing season. Herbicide treatment with glyphosate is also effective. Sesbania spp. can be controlled through mechanical means (late summer disking or mowing) or herbicide treatments with glyphosate.