Feature Article January 8, 2003
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Invasive species: Eurasian watermilfoil Invasive plants and animals have been brought here through human activities ever since the first immigrants came to this continent. There are house sparrows and starlings that were brought from Europe. Many of our common weeds originally came from there as well. In recent years weve heard about zebra mussels and spiny waterfleas that have invaded lakes in our area. Environmentalists expressed concern about the spread of purple loosestrife in the 1980s and 90s; and the West Nile virus is spreading quickly throughout the US and into Canada. Earthworms are not natives to this area, and some scientists are concerned about their long-term impact on our northern forests. Introduced species often lack natural competitors and force out native species. Although a new equilibrium is eventually established, our environment is changed forever.
During the coming months Ill present several articles about individual invasive species, their impact, and the efforts to control their spread. At this time let me start by discussing Eurasian watermilfoil. This submersed plant is in lakes throughout our region. It clogs boating channels and invades swimming areas. The plants form dense mats and provide poor habitat for waterfowl, fish and other wildlife. The masses of plants decrease oxygen and increase water temperature. Finally, when they decompose they increase phosphorous and nitrogen levels in the water. Eurasian watermilfoil is a perennial waterweed with finely dissected feather-like leaves. The leaves are arranged in whorls around the stem at each node. Milfoil is an extremely adaptable plant, able to tolerate and even thrive in a variety of environmental conditions. It appears to be spread primarily through boating activity. The weed establishes roots in water depths from 1 to 10 meters (regularly reaching the surface while growing in water 3 to 5 meters deep). It was first collected from a pond in Washington, DC in 1942. The plant was discovered in Ontario and Quebec in the 1960s. By 1985, it had been found in 33 states and the Canadian provinces of British Columbia, Ontario, and Quebec. Chemical and physical controls have been used with limited success. Because this plant spreads readily from stem pieces, mechanical controls such as cutting, harvesting, and rotovation (underwater rotortilling) are largely ineffective. Using these mechanical controls will tend to increase its rate of spread. You can control it in a local area (in swimming areas and around docks) by covering the sediment with an opaque fabric which blocks light from the plants. However, before embarking on any chemical or mechanical controls, coordinate with the appropriate authorities (MNR, MOE, Conservation Authority or DFO) to ensure you have the necessary approval. Biological controls may hold more promise. The North American weevils feed on milfoil and are located throughout our region. Recent studies have found the insect is associated with declining populations of plants. In 1999 the Kawartha Fisheries Association and Parks Canada began studying the effectiveness of weevils to control milfoil. During the summer of 2000, they studied the population of milfoil weevils on Pigeon Lake. The weevils were most numerous in areas within one metre from the shore. Sites that were developed and lacked natural vegetation had fewer weevils. This research is ongoing, but it appears that milfoil weevils have some potential in controlling Eurasian watermilfoil. Toward that end maintaining a natural shoreline to increase the weevil population may hold the key to effective control.
