Invasive Plants in PNW Ecosystems
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Experimental Comparison of Treatment Methods for Sparsely Distributed Spartina anglica Infestations.N. Kathryn Morgan, 1,3 Danelle W. Heatwole,2and Roger N. Fuller1 Spartina anglica C.E. Hubbard (common cordgrass) is an aggressive non-native plant species that has invaded estuarine ecosystems throughout northern Puget Sound, Washington. Mechanical control with heavy machinery and broadcast herbicides is effectively controlling large, monotypic cordgrass meadows. However, this treatment strategy is not effective against infestations that are sparsely distributed within native tidal marshes, and little research has been conducted to evaluate treatment practices appropriate for such conditions. In 2005, The Nature Conservancy initiated a two-year replicated experiment comparing the effectiveness, efficiency, and non-target impacts of five herbicide and manual treatments designed for widespread but low density cordgrass infestations. The study was conducted at the Conservancy’s 4,000 acre Port Susan Bay preserve, where several years of treatment and monitoring has revealed highly variable treatment effectiveness. Monitoring conducted seven weeks after treatment suggested mixed initial results for glyphosate and imazapyr herbicides, although overwinter survival is expected to expose more revealing patterns during the 2006 field season. Young plants tended to appear later in the summer, well after the herbicide treatment period. Manual digging and seedling removal proved very labor intensive and are likely inappropriate for more dense or widespread infestations. Non-target impacts to native plant species will be evaluated during the 2006 field season, but observations suggested that more trampling occurred during manual treatments. Results from this experiment are expected to provide insight into better control practices for sparsely distributed cordgrass infestations and speed the eradication of this invasive species in Port Susan Bay and elsewhere in northern Puget Sound.
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