AIS Spotlight – Eurasian Water Milfoil

Every month, we will put a spotlight on an aquatic invasive species in a re-occurring monthly article. Check it out!

Eurasian Water Milfoil – The Zombie Plant

Eurasian water-milfoil (Myriophyllum spicatum) is a commonly found invader in the Winnebago Waterways system. Many boaters, anglers, and swimmers will recognize the plant even if they don’t know it’s name.

Eurasian water-milfoil

Eurasian water-milfoil (EWM) typically grows anywhere from 3-10 feet, but some plants have been measured at over 33 feet in length! That’s as long as some school buses! The plant roots into the soil of a lake in the littoral zone, where sunlight is able to reach the bottom of the lake and plants can grow. As this plant grows, it will grow toward the water surface. Once it reaches the surface, it will continue to grow and the plant will then grow horizontally at the surface! This is why EWM is often found in large beds of tangled dense plants that criss-cross each other and from dense mats at the surface of the water.

The plant will grow out of the water when it forms a flower that resembles a small pink spike. Each plant creates both male and female flowers. Each plant produces over 100 seeds, but EWM has more success reproducing through fragmentation. A fragment or portion of the plant can break off, float to a new location and settle into the sediment, grow roots, and start a new plant (this is where the plant gets its nickname of the “zombie plant”). EWM will die back during our cold Wisconsin winters but the root system allows the plant to grow back during the following year.

Eurasian water-milfoil leaf. The leaf has pairs of leaflets that grow out of the central leaf axis.

Identification: EWM has leaves that are very feather-like that can not support themselves out of water. Leaves are arranged in whorls around the stem (radiating from a single point) with four leaves per whorl. Each leaf consists of 12-21 leaflet pairs along a central leaf axis.

So how did it get here and what’s the issue?

EWM is native to Europe and Asia and first arrived in North America in the early 1900s. It was also commonly found in the aquarium and water garden trade and most likely spread over long distances through this pathway.

As one can imagine, the ability of the plant to be broken apart and each new fragment starting a new plant elsewhere is an easy way that this aquatic invasive species is spread. As boaters go through the mats of milfoil, the propeller breaks fragments off of the original plant. The ability of the plant to grow to long lengths makes it easy to get wrapped around a trailer light as boats are loaded and unloaded. As fishing line gets stuck in the dense matting of plants, anglers pulling on the line to break it free also break parts of the plant into fragments. Swimmers and other water users can break off parts of the plant as they swim or recreate around the plant bed. These scenarios can create new populations around the lake and in other lakes as boaters, anglers, and water users accidentally transport the plant.

EWM growing in lake

In addition to causing issues to recreation, the plant also causes ecological problems. It can tolerate a wide range of water conditions and tends to thrive in areas that have been recently disturbed (either naturally or man made). The large criss-crossed plants also can also stop light from penetrating through water. Native plants that grow on the bottom of the lake are then shaded-out and can die from a lack of sunlight.

EWM looks similar to a number of native plants in the Winnebago Waterways including Northern water milfoil (Myriophyllum sibiricum). Nearly identical to EWM, Northern water milfoil only has 5-11 leaflet pairs on each leaf while EWM has more than 12 leaflet pairs. Another native plant called Coontail (named appropriately as the end of the plant resembles a racoon’s tail) is also often confused with EWM. However, the leaves on the Coontail (Ceratophyllum demersum) can support themselves out of water and display a forking pattern.

Due to the similarity between EWM and Northern water milfoil, these plants are starting to hybridize. Hybrids are starting to appear more frequently around the state and are present in the Winnebago system.

In Wisconsin, EWM is classified as a Restricted Species meaning that it is already established in the state and has the ability to cause significant environmental, economic, or human health harm.

HELP PREVENT THE SPREAD!

Every time you come off the water, make sure to follow these steps to stop the spread of EWM and other aquatic invasive species:

* Inspect boats, trailers and equipment for attached aquatic plants or animals.

* Remove all attached plants or animals

* Drain all water from boats, motors, livewells and other equipment

* Never move live fish away from a waterbody

* Dispose of unwanted bait in the trash

* Buy minnows from a Wisconsin bait dealer.

* Only use leftover minnows when either 1) fishing with them on the same body of water or 2) on other waters if no lake/river water or other fish have been added to the container.

This article was written by Chris Acy, the AIS Coordinator for the Winnebago Waterways Program covering Fond du Lac, Calumet, and Winnebago Counties.

To learn more about invasive species and their impacts to Wisconsin’s waters and economy, visit DNR.wi.gov and search “Invasive Species”.

Questions? Comments? Contact Chris Acy, our Aquatic Invasive Species Coordinator at (920) 460-3674 or chris@fwwa.org!

Winnebago Waterways is a Fox-Wolf Watershed Alliance program. The Fox-Wolf Watershed Alliance is an independent nonprofit organization that identifies and advocates effective policies and actions that protect, restore, and sustain water resources in the Fox-Wolf River Basin.