Efficacy of rotovation in controlling Eurasian watermilfoil in the Pend Oreille River, Washington

  • Published source details Gibbons M.V. & Gibbons H.L. (1988) Efficacy of rotovation in controlling Eurasian watermilfoil in the Pend Oreille River, Washington. Lake and Reservoir Management, 4, 153-160.


Action: Physically remove problematic plants

A before-and-after study in 1987–1987 in a river in Washington, USA (Gibbons & Gibbons 1988) reported mixed effects, on non-target macrophyte species, of tilling plots invaded by Eurasian watermilfoil Myriophyllum spicatum. Unless specified, statistical significance was not assessed. Along Transect 1, vegetation was initially composed of Eurasian watermilfoil (43 stems/0.1 m2) with some pondweeds Potamogeton spp. (1 stem/0.1 m2). Ten months after tilling, Eurasian watermilfoil density was significantly lower (32 stems/0.1 m2). No pondweeds were present. Along Transect 2, the vegetation was initially dominated by water-crowfoot Ranunculus sp. (44 stems/0.1 m2), with some other native species (24 stems/0.1 m2) plus Eurasian watermilfoil (9 stems/0.1 m2). Ten months after tilling, the vegetation was dominated by Canadian waterweed Elodea canadensis (45 stems/0.1 m2). There were 24 stems/0.1 m2 of other native species – including one not present before tilling: shortspike watermilfoil Myriophyllum exalbescens. There were only 3 stems/0.1 m2 of Eurasian watermilfoil. Methods: In October 1986, fifteen hectares of watermilfoil-invaded sediments were rototilled. Barge-mounted blades disturbed the sediment up to 15 cm depth, uprooting macrophytes and reducing their density. Vegetation was surveyed before tilling (October 1986) and 10 months after (August 1987), in 5–10 quadrats (0.1 m2) along each of two transects.

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