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   Potamogeton crispus (aquatic plant)     
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      Photo: courtesy of USDA NRCS Wetland Science Institute. - Click for full size   Robert H. Mohlenbrock @ USDA-NRCS PLANTS Database - Click for full size
    Taxonomic name: Potamogeton crispus Linnaeus, 1753
    Common names: curly pondweed (English), curly-leaved pondweed (English)
    Organism type: aquatic plant
    Potamogeton crispus is an aquatic plant that grows in fresh and slightly brackish waters. It becomes invasive in some areas because of its tolerance to low light and low water temperatures. These tolerances allow it to outcompete native plants in the spring. Using this life cycle, P. crispus can be controlled best in spring or early summer when native species are still dormant and temperatures are low enough for endothal herbicides to be effective.
    Potamogeton crispus “is a submerged, perennial aquatic plant easily identified by lanceolate, reddish-green, wavy leaves with finely toothed margins. The leaves are 0.5-1.5cm wide and 3cm to 10cm long. Stems are branched and somewhat flattened. P. crispus flowers are small, somewhat inconspicuous, and arranged in a dense spike on a curved, 2.5cm to 5cm stalk” (DECFW et al., 1998). Plants can grow to 4m in deep water, with stunted rosette forms of the plant occurring in very shallow water < 0.3m (NIWA, 2004).
    Similar Species
    Potamogeton spp.

    Occurs in:
    estuarine habitats, lakes, water courses, wetlands
    Habitat description
    Potamogeton crispus is found in freshwater lakes, ponds, rivers and streams, and in slightly brackish waters. It is tolerant of low light, low water temperatures, and is a species of alkaline or nutrient-rich waters. P. crispus will invade shallow as well as deep water areas (DECFW et al., 1998).
    General impacts
    Potamogeton crispus can grow in dense beds which outcompete native aquatic plants. The dense surface mats may also interfere with water-based recreational activities (DECFW et al., 1998).
    Crowell (UNDATED) states that “in some lakes, P. crispus coexists with native plants and does not cause significant problems. In other lakes, it becomes the dominant plant and causes significant problems.” These problems include interfering with late spring and early summer recreation due to the formation of dense mats and an increase in phosphorus concentrations causing an increase in algae blooms and a pile up of dying P. crispus along the shore, both due to its mid-summer die back.
    According to USDA-NRCS (2002), P. crispus tends to increase oxygen levels at day-time and produce substantial organic material in aquatic environments. This pondweed shelters small fish and aquatic insects that provide food for larger fish and amphibians.
    Geographical range
    Native range: Eurasia, Africa, Australia and North America (Global Compendium of Weeds).
    Known introduced range: All of the continental United States except Maine and South Carolina (USDA-NRCS 2002) and Ontario in Canada (CWS, 2003); New Zealand (NIWA, 2004).
    Introduction pathways to new locations
    Floating vegetation/debris: According to Crowell (UNDATED), P. crispus can spread by plant fragments attached to boats and equipment that are not properly cleaned.
    Ignorant possession: According to Crowell (UNDATED), P. crispus can spread by plant fragments attached to boats and equipment that are not properly cleaned.

    Local dispersal methods
    Boat: According to Crowell (UNDATED), P. crispus can spread by plant fragments attached to boats and equipment that are not properly cleaned.
    Water currents: According to Crowell (UNDATED), these ‘turions’ disperse by water movement.
    Management information
    Preventative measures: Curlyleaf can spread from plant fragments, so it is important to clean all vegetation off boats and equipment before leaving water access.

    Physical: Curlyleaf pondweed has a unique lifecycle which influences management options for its control. It is the first pondweed to come up in spring and dies back during mid-summer. When most aquatic plants are growing, curlyleaf plants are dying back. Before they die, they form vegetative propagules called turions (hardened stem tips) that disperse by water movement. Turions lay dormant during the summer when native plants are growing, and most germinate when most native vegetation has died back. Long-term management of curlyleaf will require the reduction or elimination of turions to interrupt its life cycle. Management activities should be undertaken in spring or very early summer to have the maximum benefit. Mechanical control includes raking, cutting or harvesting vegetation. Raking and hand cutting generally remove the plants at the sediment surface while harvesting removes the top 5 ft of the plant. Mechanical methods control plants in the specific areas where they are causing a nuisance, and there is immediate relief from the nuisance. There is some evidence that early season cutting of pondweed at the sediment surface can prevent turion production (McComas and Stuckert, 1996).

    Chemical: According to APIS (2002), chemicals that can be used to control include the herbicides diquat (Reward, Weedtrine-D), endothall (Aquathol, Hydrothol 191), and floridone (Sonar A.S., Sonar SRP). Corwell recommends endothall-based herbicide, such as Aquathol K, because it is effective in 15 degrees C (60 degrees F) water allowing for earlier treatment.

    DECFW et al. (1998) states that “Potamogeton crispus is a species of alkaline or nutrient-rich waters.”
    According to DECFW et al. (1998), “Potamogeton crispus spreads primarily by burr-like winter buds called ‘turions’ which are hard and prickly. One plant may produce hundreds of turions, which are then dropped to the sediment to germinate the following year. According to Crowell (UNDATED), these ‘turions’ disperse by water movement.
    It also reproduces vegetatively from rhizomes and stem fragments. P. crispus can also spread by plant fragments attached to boats and equipment that are not properly cleaned.
    Seed is set and seedlings are commonly found at field sites. In shallow water it may also set seed and behave more like an annual, whilst deeper water plants persist as perennials (NIWA, 2004).
    Reviewed by: Dr Tom Madsen. Department of Plant Ecology, University of Aarhus Nordlandsvej 68, DK-8240 Risskov Denmark
    Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
    Last Modified: Friday, 31 March 2006

ISSG Landcare Research NBII IUCN University of Auckland