Evaluation of a New Biological Control Pathogen for Management of Eurasian Watermilfoil

This technical note describes the results of an aquarium study to evaluate the effectiveness of a potential fungal pathogen in managing the nuisance submersed plant Eurasian watermilfoil Myriophyllum spicatum L. (Eurasian watermilfoil; hereafter called milfoil) was first documented in the United States in 1942 but its introduction could have taken place much earlier (Couch and Nelson 1985). It now occurs in lakes, ponds, reservoirs, or rivers in 48 states (excluding Wyoming and Hawaii) and in the Canadian provinces of British Columbia, Ontario, and Quebec. Herbarium records indicate that there could have been multiple introductions, as early reports came from widely separated locations including Washington DC, the Midwest, and Arizona and California (Smith and Barko 1990). Milfoil spreads naturally by fragmentation and stolons, and anthropogenically on boating equipment. Like other aggressive invasive species, milfoil displaces native species, thereby reducing biodiversity. Its ability to grow at low temperatures allows it to quickly reach the water surface, forming a canopy that shades out other aquatic vegetation (Madsen et al. 1991). Excessive growth adversely affects recreational activities such as swimming, boating, and fishing and degrades the aesthetic appeal of a water body. Additionally, excessive growth results in clogged intakes of industrial and power-generating facilities, lowered dissolved oxygen, and increased mosquito breeding sites (Bates et al. 1985). Traditionally milfoil has been controlled with mechanical removal or herbicide applications. According to Sorsa et al. (1988), the former is cost prohibitive and the latter potentially controversial due to real or perceived threats to human health and the environment. Biological control has been studied as an option for milfoil management for over 40 years.