Curled Pondweed

General: Herbaceous, partially or entirely submersed aquatic species.

Flowers: Small and reddish-brown, with 4 petal-like lobes, arranged in a dense spike on a curved 2.5 – 5 cm stalk. Flower spikes often emerge above the water surface.

Stems: Light green or yellowish-white, branched and flattened. Stems can be over 1 m tall in deeper waters.

Turions: Bur-like, prickly buds that form along the stem just above the site of leaf attachment. Turions break free and form new plants; they can stay viable for up to two years.

Leaves: Lance-shaped and somewhat translucent. They appear reddish-green when submerged, but green out of the water. Leaves are 0.5 – 1.5 cm wide and 3 – 10 cm long, wavy (lasagna-like) and arranged in a spiral along the stem.

Native to Eurasia, Africa and Australia. Introduced to the USA in the mid-1800s, likely unintentionally, through fish stocking operations.

Curled pondweed is generally found in ponds, rivers, wetlands, lakes, streams and brackish waters 1 – 3 m deep. This plant prefers alkaline and eutrophic waters. It can be found in disturbed sites and various substrates, like gravel, fine sand, loamy mud and clay. It can also survive over winter under ice.

Ecological: 

• Outcompetes native aquatic vegetation by limiting the light available for photosynthesis.
• Can cause algal blooms and ultimately eutrophication in water bodies, which may result in the death of fish and other aquatic species due to hypoxic conditions.

Economic:

• Decreases the real estate value and the aesthetic appeal of a waterbody.
• Negatively impacts tourism by impeding recreational activities such as boating, fishing, and swimming.

Cultural

Benthic barriers made from a variety of materials (such as heavy, opaque plastic) can be placed over an infestation to prevent sunlight from reaching the plants and restrict upward growth. The installation should occur during spring to prevent the plants from exceeding 0.5 m tall and greatly increasing their biomass.

However, keep in mind that benthic barriers affect all vegetation, not just the undesirable curled pondweed.

Mechanical

Raking and hand-cutting curled pondweed is a relatively effective mechanical control method but should be performed early in the season. Ensure that as many plant fragments are removed as possible, as any left could produce new plants. Cutting at the sediment surface has been shown to reduce turion production.

Mechanical methods generally need to be repeated for several years, and monitored thereafter to ensure the plant doesn’t re-establish.

Chemical

Herbicides cannot be applied in aquatic environments in Canada. Herbicide control is not recommended for this species.

Biological

Sterile triploids of the white amur grass carp (Ctenopharyngodon idella) can be used to control curled pondweed infestations, as they are a relatively non-selective herbivorous species. Careful monitoring of feeding impacts is necessary, as the fish might also consume desirable aquatic vegetation.