Milfoil and Other Invasive Aquatic Plants in Maine

 

What are the watermilfoils? Watermilfoils are rooted, submerged aquatic weeds found naturally in lakes and streams. Five varieties of watermilfoils are native to Maine and are part of the natural lake ecosystem. Two non-native watermilfoils threaten the quality of Maine fresh waters; Variable leaf milfoil (myriophyllum heterophyllum) is already present in 27 Maine lakes and streams. Eurasian watermilfoil (myriophyllum spicatum), the more aggressive colonizer of the two, has been found in one Maine water body.

Variable Leaf Milfoil in the Songo River in 2006

Where they come from and how do they spread? Most aquatic invasive plants began as aquarium plants; many were brought overseas from Southeast Asia. When aquaria were emptied into lakes or streams, the plants proliferated. Eurasian watermilfoil was first noticed in the 1970’s in the Great Lakes. Since then it has gradually spread, lake by lake, across North America. Variable leaf milfoil is native the Southeastern and Midwestern United States. It was introduced into Connecticut as an ornamental in 1932 and has proliferated in the Northeast. Many aquatic plants reproduce by fragmentation, so when a motorboat or jetski passes through a colony of plants, the chopped up pieces are each capable of forming a new plant. Invasive aquatic organisms can also travel in ballast water aboard ships. This is one of several ways that plants and animals are being dispersed globally into ecosystems foreign to them.

Eurasian Milfoil

Why are non-native plants so bad? Economic and Recreational Impacts Much of Maine’s economy is based on recreation and tourism; Maine’s lakes bring in $2.3 billion dollars annually into Maine’s economy. The visitors to those lakes spend a total of $3.5 billion in Maine each year, $1.8 billion of which goes directly to the income of Maine residents at 50,000 jobs statewide. As the quality of the waterways decline people are less likely to visit them as a recreational resource and put money into local economies. Additionally, a 2001 Maine DEP report stated that if Maine suffers infestations even of a ‘fraction’ of those in Vermont than lakefront landowners can expect a property value loss of $12,000 each on average. Ecological Impacts Ecological impacts of invasive plants are difficult to enumerate. The most obvious impact they have upon native communities is out competition of indigenous plants. Invaders are free of the checks and balances that accompany co-evolution between native plants and competing and predacious organisms in the native’s ecosystem. Because of this, they may have a competitive edge for resources over native species. The implications of the loss of native plants are far reaching. Native plants act as both a food source and habitat to form the backbone of the aquatic food web. By changing the available habitat and food source invasive plants can drastically alter that delicate balance. A 2004 study even suggest that changes in an aquatic food web are able to influence species interactions in the adjacent terrestrial habitat, meaning that milfoil infestations can also affect the ecosystems near the infested water body as well.
	Eurasian Milfoil
	Hydrilla

Control Methods

There are a variety of methods available to control the populations of invasive aquatic plant infestations. The goal of management is not always to eliminate the invaders but also to preserve or alleviate the pressure upon the quality of a water body as a recreational, economic, or ecologically viable area.

• Mechanical Removal
• Physical Removal
• Biological Control
• Chemical Control
• Further Readings

What can you do about the threat of milfoil?
If you are concerned about the threat of milfoil, there is something you can do. Start by taking the following steps:

• Educate yourself.
• Read our milfoil web page or visit some of the links below.
• Educate others. Tell everyone you know about the threat, especially if they are a boater who might inadvertently spread the plant.
• Volunteer to work in LEA’s milfoil prevention program. We are looking for people who can volunteer at boat launches during the summer educating boaters and checking their boats for milfoil. We are also looking for volunteers “weed-watchers” to survey local lakes for milfoil. Link to Volunteer Opportunities. Hours are very flexible. Call the LEA office for more information.

Milfoil Links

Maine Center for Invasive Aquatic Plants

Universtiy of Florida (Eurasian Milfoil)

United States Department of Agriculture (Variable Leaf Milfoil)

New Hampshire Variable Milfoil Control Research Project

 

Hydrilla Links

University of Florida, Center for Aquatic Plants Hydrilla Verticillata "The Perfect Weed"

Universtiy of Florida, Center for Invasive Aquatic Plants and Sea Grant

University of Florida, Article on Hydrilla Verticillata