Nymphaea odorata can be controlled by cutting, harvesting, covering with bottom barrier materials and aquatic herbicides. After control treatments dead and decomposing leaves and rhizomes may form floating mats in the lake. Removing all dead materials from the water is recommended (Washington Department of Ecology 2005).
Mechanical: Persistent picking of emerging leaves every other day during two to three growing seasons will eventually kill the plants. Localized control (in swimming areas and around docks) can be achieved by covering the sediment with a opaque fabric which blocks light from the plants (bottom screening). Managers of reservoirs and some lake systems may have the ability to lower the water level as a method of managing aquatic plants, but the response of the N. odorata to water level draw down has been variable (Washington Department of Ecology 2005, and Washington Department of Ecology, 2003).
Cutting is less efficient than harvesting because cut plants must then be removed from the water. Harvesters both cut and collect the plants. Cutting and harvesting must occur several times a year in order to be effective (Washington Department of Ecology, 2003).
Underwater rototilling (called rotovation) was successfully used to remove N. odorata from a small Seattle area lake where the drowning of two people was attributed to the presence of dense plant beds. Rotovation dislodges the large, fleshy N. odorata rhizomes which can then be removed from the water. Experimentation has also occured using a barge-mounted backhoe to excavate N. odorata rhizomes from the sediment. Both methods result in permanent removal of the plant, but require a number of environmental permits before proceeding (Washington Department of Ecology, 2003).
Chemical: Glyphosate reportedly is an excellent herbicide to control N. odorata and it can be directly applied to floating leaves. Two applications of glyphosate will most likely be required to achieve control. Control has also been obtained with endothall dipotassium salt and fluridone, but must be applied to the water (Washington Department of Ecology, 2003).
Location Specific Management Information
Approximately 2.32 acres of wetlands were filled in Eastlake, Ohio to construct a residential housing development. In accordance with Section 404 of the Clean Water Act, wetlands mitigation was performed to compensate for these impacts. To satisfy mitigation requirements, existing wetlands were enhanced by excavating a two-acre, deep-water marsh. The wetlands had previously been dominated by Phragmites australis (common reed), a non-native nuisance species that thrives in disturbed urban wetlands. The mitigation wetlands were excavated to depths varying between 1.5 and 4 feet. Nuphar advena (spatterdock), Nymphaea odorata (fragrant water-lily), Pontederia cordata (pickerelweed), and Utricularia vulgaris (common bladderwort) were planted. Golden shiner (Notemigonus crysoleucas) and mud minnow (Umbra limi) were introduced in the deep-water wetlands. Bird boxes and a bat house were installed to attract wildlife. Birds, bats, mud minnows, and bladderwort, a carnivorous plant, provide a multi-level control program for larval and adult mosquitoes and nuisance insects. The enhanced wetlands, existing natural wetlands, and upland buffer provide a 10-acre park-like open space within this residential housing project (Wise et al. 1999).
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