Eurasian Watermilfoil

Daniel Kelly | Fondriest Environmental

Like other aquatic invasive species, Eurasian watermilfoil was accidentally introduced to North America. It originates from Europe, and made the leap in the 1940s.

By some accounts, aquarium owners are to blame for its spread, as some are believed to have released the contents of their tanks into local waterways. But others point to ships, whose propellers could have easily gotten tangled up in watermilfoil and taken stems with them to new ports.

Dense Myriophyllum spicatum, Eurasian watermilfoil, canopy at lake surface. Cayuga Lake, Ithaca, New York, August 1989. (Credit: Robert L. Johnson)

Regardless of its method of entry, Eurasian watermilfoil was difficult to stop once it got in. There was much less public awareness in the 1940s of the threat of invasive species, so it was met with little resistance. And given its natural tendency to expand prolifically, watermilfoil quickly took hold in new waterways.

Its expansion was aided by its stem-and-leaf system that produces seedling runners that cling to animals or vehicles for easy transport to new areas. It only takes a single segment of stem and leaves to take root and form a new watermilfoil colony.

Distribution of Eurasian watermilfoil in the continental United States. (Credit: U.S. Department of Agriculture)

The detrimental effects that Eurasian watermilfoil has often come from the way it grows into dense beds. The thick sections can reduce the amount of light penetrating through lakes or ponds, which shades out native plants. They also provide more hiding spaces for smaller fish, possibly diminishing food supplies available to larger fish and pushing the ratio between predators and prey out of balance.

Prevent Its Spread

With well-established populations of native plants in lakes and waterways, Eurasian watermilfoil has difficulty expanding into new areas. This marks the importance of having good invasive species controls already in place.

Regularly inspecting boat propellers, keels or rudders for the presence of watermilfoil can help to keep it in check. This goes along with common boat and gear maintenance tips following use – clean, drain and dry everything before heading out to new waterways.

Though difficult to remove once it is established, water managers have found success with aquatic herbicides, including Sonar brand, to eliminate Eurasian watermilfoil. Selective herbicides 2, 4-D and triclopyr-TEA have also shown promise in managing watermilfoil infestations. In addition, use of the milfoil weevil, a biological control, could prove to be a valuable management tool.

Sources:

Eurasian Watermilfoil

Prevent Its Spread

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