P. crispus is an herbaceous, submersed aquatic species that typically grows with stem up to 1m long. Its sessile, linear leaves are light to dark-green. They are typically from 1.2-9 cm long, 4-10 mm wide and are spirally arranged on flattened cauline stems. Leaves are homophyllous, often undulate, with obtuse apices and 3-5 veins. Margins are finely serrate. Lacunae are conspicuous and occur in rows of 2-5 along the midrib of the leaf. Stipules are not fused to the leaf and persistent, though inconspicuous. Leaves and stem are lax;the plant is either entirely submersed or nearly entirely submersed with some leaves floating at the surface. Nodal glands in this species are entirely absent. Inflorescences are unbranched and emersed, generally terminal (Flora of North America Editorial Committee, 1993). Flowers are tiny, with four petal-like lobes on spikes 1-3 cm long on stalks up to 7 cm long (Washington State Department of Ecology, 2008). Sessile reddish-brown single-seeded fruits are unkeeled and measure 6 x 2.5 mm. Fruits have a small recurved beak that measures 2-3 mm. Embryo has full spiral. Short, bur-like hardened turions, in which internode length is extremely shortened, measure 1.3-3 by ~2 cm, are common and can be either apical or axillary (Flora of North America Editorial Committee, 1993;USACE, 2002).
Formal aquatic plant surveys are generally necessary for the early detection of this species.
Similarities to Other Species/Conditions
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P. crispus is easily distinguished from other pondweeds by leaf and fruit morphology, phenological characteristics, and turion production (Iida et al., 2004). P. crispus is unique in that its leaf margins are finely serrate. Difficulties in identification may occur very early or late in the growing season, when turions are germinating. At these times, the plant develops a winter growth form with very slender, limp, blue-green leaves (Bolduan et al., 1994). Serrations are present in the winter growth form, though are not as conspicuous. However, members of the genus Potamogeton hybridize readily, and produce individuals with intermediate morphological characteristics (Kaplan and Fehrer, 2004).
Prevention and Control
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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Prevention
The vegetative propagules of this species are very easy to spread. Therefore, educational programs are usually necessary to decrease this form of human-mediated spread. Teaching users how to clean equipment in a way that decreases the chance of transmission is one way to lessen the impact of the human vector. Several of the USA states have legislated regulation of the purchase, transportation, and introduction of this species.
Rapid Response
This species produces turions prolifically, and because the turions can stay dormant yet viable for at least 2 years (Tomaino, 2004), rapid response to decrease turion deposition is integral to successful management.
Public Awareness
Numerous educational campaigns have been directed at informing the public about the danger of aquatic invasive species. Agencies in areas in which P. crispus is particularly problematic commonly distribute informational materials about its identity as well as how to report new invasions. Other educational campaigns have been directed towards informing the public about how to clean equipment in order to prevent the transportation and spread of invasive species.
Eradication
No reports of eradication exist in the literature.
Control
Cultural control and sanitary measures
Turions are easily transportable and can remain dormant for up to 2 years. Thus, it is extremely important to decrease the instances of accidental introduction by addressing humans as a vector. By establishing guidelines on how to properly clean equipment, dispose of water, and identify target plants, it is likely that instances of accidental transportation and release will be fewer.
Physical/mechanical control
Mechanical harvesting may be used to obtain some nuisance relief, but reviews of efficacy of control are mixed. In Michigan, USA the dominance of P. crispus was only reinforced by harvesting at the expense of natives (Bolduan et al., 1994), whereas it has been shown elsewhere that early season cutting at the sediment surface prevented turion production (ISSG, 2006). Some have used winter drawdowns as a means of control, but the literature reports no significant impact of overwinter drawdown on P. crispus (Nichols and Shaw, 1986). Shallow dredging also has mixed reviews, at times there seems to be little effect, and in some cases lasting control has been achieved (Tobiessen and Snow, 1984;Tomaino, 2004).Other mechanical methods including benthic barriers, hand removal, rotovation and shading have been reported as successful (USACE, 2002).
Movement control
Screening has been used to stop the movement of turions. However, because plants can spread via fragments, much attention has been given to decreasing human-mediated dispersal. The plant is on a number of state noxious lists. Some states have put in place legislation to regulate the sale, transportation and introduction of P. crispus.
Chemical control
P. crispus is sensitive to 2,4-D, especially during early spring (Wolf and Madsen, 2003;Belgers et al., 2007). P. crispus is susceptible to endothall-based herbicides (Skogerboe and Getsinger, 2002). It is also suggested that treatments occur in early spring in order to lessen the impacts on the native plant community (ISSG, 2006). The herbicides fluridone and diquat have also been used and in general, chemical treatments provide relief for one growing season (ISSG, 2006).
Related invasive species
- Potamogeton crispus
Related Farm Practice
- Ecology
- Light
- Flora
P. crispus is a productive, submersed macrophyte that is non-native and invasive in temperate areas of North America, New Zealand, and southern South America (Kaplan and Fehrer, 2004). The species is listed as a noxious or prohibited weed in several areas of the USA (USDA-NRCS, 2008). The species is a cold weather strategist, which allows it to establish early in the growing season (Nichols and Shaw, 1986). Unlike most macrophytes, P. crispus plants typically die back by early summer and lie dormant until temperatures decrease again in autumn (Bolduan et al., 1994). It is also a productive species that tends to form monocultures, thereby decreasing the amount of light available to other species (Engelhardt, 2006). However, its impact on native species is disputed in the literature. Some authors state that early emergence helps P. crispus out-compete natives, while others aver that its characteristic summer die-back removes it from such competition (Bolduan et al., 1994). However, this documented summer senescence is problematic, as the inevitable decay of organic material and resultant nutrient release can stimulate algal blooms and lead to dissolved oxygen crashes. Additionally, this species is particularly hard to control due to its prolific production of turions (Yeo, 1966).
Given this species’ tendency to grow in monocultures with high productivity, it has been reported to cause decreases in biodiversity by out-competing native plants (Tomaino, 2004). However, it should be noted that the impact of this species on the native community is disputed, with some authors concluding that because the plant acts like a winter annual it does not negatively impact native species (Bolduan et al., 1994). It can be productive, but is not generally reported as a nuisance in its native range.