Invasive Aquatic Plants

 Curly-leaf pondweed (Potamogeton crispus)

Common names: Curly cabbage, crisp pondweed.

Location: Grows from the shore to depths of up to 15 feet.

Description: Leaves are somewhat stiff and crinkled, approximately 1/2-inch wide and 2 to 3 inches long; leaves are arranged alternately around the stem, and become denser toward the end of branches; produces winter buds can be confused with claspingleaf pondweed.

Hints to identify: Has small "teeth" visible along edge of leaf; begins growing in early spring before most other pondweeds; dies back during midsummer; the flower stalks, when present, stick up above the water surface in June; appears reddish-brown in the water, but is actually green when pulled out of the water and examined closely.  Easily confused with claspingleaf pondweed, which has leaves with no "teeth" around their edges.

Importance of plant: Provides some cover for fish; several waterfowl species feed on the seeds; diving ducks often eat the winter buds.

Management strategy: See DNR regulations.  Like Eurasian watermilfoil, curlyleaf pondweed is not native to the United States and often causes problems due to excessive growth. When control is necessary, herbicides and harvesting can be effective.  Grants are available for control efforts on a lake-
wide basis.

[Eurasian watermilfoil] Eurasian watermilfoil (Myriophyllum spicatum)

Eurasian watermilfoil typically has 12 to 21 pairs of leaflets.  The native northern watermilfoil, with which it is often confused, usually has 5 to 9 pairs.  Eurasian watermilfoil was accidentally introduced to North America from Europe. Spread westward into inland lakes primarily by boats and also by waterbirds, it reached Midwestern states between the 1950s and 1980s.

In nutrient-rich lakes it can form thick underwater stands of tangled stems and vast mats of vegetation at the water's surface. In shallow areas the plant can interfere with water recreation such as boating, fishing, and swimming. The plant's floating canopy can also crowd out important native water plants.

A key factor in the plant's success is its ability to reproduce through stem fragmentation and runners.  A single segment of stem and leaves can take root and form a new colony.  Fragments clinging to boats and trailers can spread the plant from lake to lake.  The mechanical clearing of aquatic plants for beaches, docks, and landings creates thousands of new stem fragments.  Removing native vegetation creates perfect habitat for invading Eurasian watermilfoil.

Eurasian watermilfoil has difficulty becoming established in lakes with well-established populations of native plants.  In some lakes the plant appears to coexist with native flora and has little impact on fish and other aquatic animals.

Likely means of spread: Milfoil may become entangled in boat propellers, or may attach to keels and rudders of sailboat.  Stems can become lodged among any watercraft apparatus or sports equipment that moves through the water, especially boat trailers.

Non-native waterlilies (Nymphaea spp.)

Appearance: Perennial aquatic herbaceous plant.

Leaves: Floating or slightly immersed in shallow water. Round with "v-shaped" opening or cleft.

Flowers: Unlike native waterlilies which have white flowers (Nymphaea odorata) or yellow flowers (Nuphar variegatum), most exotic waterlilies have brightly colored flowers including pink, purple, and red.  Exotics may also have white or yellow flowers and can be difficult to distinguish from native species. Individual flowers have numerous petals and may bloom all summer.

Seeds: Hybrid species may or may not produce viable seeds.

Roots: Fleshy, buried rhizome that can spread extensively..

Ecological Threat:  Non-native waterlilies may invade ponds and lakes.  Hardy species may expand and choke out native plants.  Non-native waterlilies are legally sold as water garden plants but are occasionally illegally planted in public waters.  Non-native waterlilies sold for water gardening may also contain "hitchhiker" exotics like harmful exotic submerged plants or zebra mussels. Therefore, even though some exotic waterlilies do not survive Minnesota winters, the more harmful "hitchhiker" exotics can be introduced to our lakes when nursery or mail order species are planted.

This plant is a regulated exotic species and is legal to purchase and possess, but may not be introduced into a free-living state, including public waters or other sites where the species is beyond control of a person.

Control Methods:  A permit is required to work in public waters

Mechanical:  Small populations can be removed by digging. Entire underground tuber must be removed.  Tubers that are not removed from the water may drift to a new location and regrow.  Hand dig isolated plants with care, root fragments can spread and sprout.

Chemical:  Non-native waterlilies are susceptible to control by aquatic herbicides.  However, to date, the DNR has not attempted herbicide control of these exotics because they grow in close proximity to native waterlilies which would also be damaged by any herbicide application

Biological:  None

Brittle Naiad (Najas minor), also called Brittle Waternymph

Appearance:  Submersed aquatic plant.

Leaves:  Leaves are opposite (leaves are in pairs along the stem), but leaves sometimes appear to be in a whorl at tip.  Leaves are 1 to 2 inches long, toothed, stiff, and pointed.

Flowers:  Small and inconspicuous. Found in leaf axils.

Reproduction:  Brittle naiad is an annual plant that spreads by seeds and plant fragments. The plant is very brittle so it easily breaks into pieces which can spread the plant to new locations. Seeds mature in summer and late fall.  Seeds germinate in the spring.

Note on identification:  Brittle naiad can be easily confused with native pondweeds and naiads.  Brittle naiad differs from coontail in that brittle naiad leaves are in pairs of two while coontail leaves are in whorls of 4 or 5.

Ecological Threat:  Brittle naiad is native to Europe and Asia and has been introduced to the United States. Brittle naiad can form dense mats that outcompete native species and can interfere with recreational activities such as boating, swimming, and fishing.  Brittle naiad is a prohibited invasive species in Wisconsin

Prevention:  Brittle naiad is reported in very few lakes in Wisconsin.  By cleaning all plant parts off of boats and  water-related equipment, we can prevent the spread of brittle naiad to additional lakes.

Mechanical or chemical:  See DNR regulations for submersed aquatic plant management strategies and  regulations. Type your paragraph here.

Lake  Mallalieu Association