Efficacy of Rotovation in Controlling Eurasian Watermilfoil in the Pend Oreille River, Washington

Abstract

ABSTRACT Full-scale mechanical rotovation of Eurasian watermilfoil (Myriophyllum spicatum) beds was conducted at selected sites along the Pend Oreille River in eastern Washington during the fall of 1986. Fifteen hectares (36 acres) of milfoil-infested river sediments were mechanically tilled to dislodge rootcrowns from the substrate. Treatment was performed by a prototype float-mounted rotovator equipped with a 2.5 m (8-foot) wide pivoting rototiller head. Treatment effectiveness was quantitatively assessed by comparing changes in stem density of M. spicatum in the plot before and after rotovation. Milfoil stem density reductions of 63 to 90 percent were observed in the rotovated area immediately after treatment. Carryover stem density reduction of 25 to 70 percent measured in the growth season following the 1986 rotovation treatment suggested that control of M. spicatum growth for greater than the season of treatment is possible. Efficiency of milfoil root removal by rotovation was dependent on substrate type, operator skill, and adequately powered machinery. Rotovation appears to be a most promising control technology capable of achieving high rates of milfoil root removal and maintaining long-term reductions in plant growth.