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Water-milfoil plants in water

Arrival Date

Eurasian water-milfoil is an underwater aquatic plant native to Europe, Asia, and northern Africa. Eurasian milfoil first arrived in Wisconsin in the 1960s. By the 1990s, it was found in more than half of Wisconsin counties, including shallow bays in Lakes Michigan and Superior and Mississippi River pools. It has continued to spread - today there many efforts across the state to protect our waters from this and other invasive species.

How to Identify

This milfoil is the only non-native milfoil species in Wisconsin - seven native species are found here. It is easiest to identify when it is blooming or has fruits on it. Eurasian water-milfoil has slender stems encircled by feathery leaves in groups. The stems branch and commonly grow to lengths up to 10 feet. Eurasian water milfoil produces small, 4-parted flowers on a spike that sticks out of the water two to four inches. The flowers are either four-petaled or without petals. The fruit is a hard, capsule with four seeds. The plant stem is often reddish-brown. Look for 12-21 pairs of leaflets per leaf to help distinguish Eurasian water-milfoil from Northern water-milfoil, the most similar native milfoil. The native plant typically has 7-11 pairs of leaflets. Don't mistake the common plant called coontail for the milfoil, it does not have individual leaflets.

Habitat & Lifecycle

Eurasian water-milfoil is found in places with lots of nutrients. It likes heavily used lakes, disturbed lake beds, and lakes that get a lot of nitrogen and phosphorous runoff. Warmer lakes can cause the milfoil to flower and reproduce more often in one summer.

Freaky Fact

Like other plants, Eurasian water-milfoil uses seeds to reproduce, but it also reproduces by making fragments of the plant after fruiting once or twice during the summer. These shoots are carried downstream by water currents and spread easily. Milfoil is also spread by boats, motors, trailers, bilges, live wells, or bait buckets, and can stay alive for days if kept moist.

Effects of invasion

This invader grows quickly in spring and forms a dense leaf canopy in the water that shades out native aquatic plants. Because it can spread rapidly by fragmentation, it can block out sunlight needed for native plants to grow. This can lead to areas where all the plants are just Eurasian water-milfoil, which is not a diverse habitat. This disrupts predator-prey relationships by keeping out larger fish, and takes away nutrient-rich native plants that waterfowl need. Eurasian water-milfoil may also lead to poor water quality and algae blooms in infested lakes. Thick stands of Eurasian water-milfoil also make it hard to have fun in the water when you want to go swimming, boating, or fishing. Nobody wants to get tangled up in that long, stringy mess! The flat yellow-green mat of vegetation can also make a lake look "infested" or "dead."

Prevention & Control

Preventing milfoil from reaching a lake or spreading is extremely important. There are many ways to help:

  • Prevent nutrients from reaching lakes and feeding milfoil colonies. You can plant a rain garden in areas that run off into the lakes and streams.
  • Inspect and remove all aquatic plants from your boat, moter, trailer, and fishing equipment before you leave a lake or river.
  • Hand pull or rake the plants, but be careful to remove fragments from the water and the shore. Use the plants away from the water as garden mulch. Plant native plants in their place to stabilize the bottom, build nurseries for small fish, attract waterfowl, and prevent new milfoil invasions.

Lake managers and biologists also use these techniques:

  • Mechanical cutters and harvesters "mow" large colonies that grow at beaches and boat landing which breaks up the milfoil canopy. But this method removes all aquatic plants and creates shoot fragments.
  • Biological Control: A plant-eating weevil native to North America likes to eat the stems and leaves of Eurasian water-milfoil. Native aquatic plant species are not at risk from the weevil's introduction. Additional research is needed before we know if weevils will be effective.