Brazilian watermilfoil, parrot’s feather, parrot-feather, parrotfeather, parrot feather watermilfoil, Enydria aquatica (Vell.), Myriophyllum brasiliense (Camb.), Myriophyllum proserpinacoides (Gillies ex Hook. and Arn.)

The submersed shoots, similar to those of Eurasian watermilfoil (M. spicatum), are comprised of whorls of four to six filamentous, pectinate leaves, 1.5 to 3.5 cm long, arising from each node (Mason 1957, Washington State Department of Ecology 2011). Submersed leaves are reddish orange. When the submersed shoots reach the water surface, plant growth changes and begins to creep along the water surface with extensive branching from nodes followed by vertical growth of emergent stems (Moreira et al. 1999).

Small, white flowers occur in the leaf axils on the emergent shoots and are approximately 1/16 inch long (Washington State Department of Ecology 2011). Parrot feather lacks structures for storage, dispersal, and perennation (e.g., tubers, turions, and winter buds), and therefore stolons serve all these functions (Sytsma and Anderson 1993).

Parrot feather is a dioecious species, however only pistillate (female) plants are found outside of South America. Staminate (male) plants are rare even in native populations of South America (Orchard 1981). For this reason, seed production is not known to occur (Aiken 1981) and reproduction is exclusively vegetative in North America (Orchard 1981). Reproduction occurs by fragmentation of emergent and/or submersed shoots, roots, rhizomes, or attached plant fragments (Center for Aquatic and Invasive Plants, UF/IFAS 2010; Les and Mehrhoff 1999; Mabulu 2005).

Parrot feather has an annual growth pattern, forming shoots in spring from overwintering rhizomes as water temperature increases. Rhizomes provide support for adventitious roots and buoyancy for emergent summer growth. Flowers usually appear in spring, or in fall for some plants. The plant usually dies back to its rhizomes in the autumn (Mabulu 2005).

Potential pathways of introduction: Natural dispersal through waterbody connections; Hitch-hiking or fouling of recreational gear, boat structures, fauna, or other objects entering the Great Lakes from surrounding region; Unauthorized intentional release from live trade; Accidental introduction to Great Lakes by escapees.

With established nonindigenous populations in states adjacent to the Great Lakes, parrot feather has potential to be introduced to the Great Lakes from nearby water bodies. So far, a fragment of parrot feather was found floating in the Detroit River in 2016. No additional parrot feather has subsequently been found in the Detroit River (pers. comm William Keeper). Additional populations have been found inland above the high water mark have been observed in Michigan, Ohio, and Indiana (pers. comm. William Keeper, Mark Warman, Wersal and Madsen 2011). Fragments of this plant can be transported by river currents and could also become attached to or entangled with recreational boats (e.g., propellers, trailer tires) or fishing gear. Its rhizomes are very tough and can be transported long distances on boat trailers, surviving for up to a year when kept moist and cool (Washington State Department of Ecology 2003). 

Parrot feather has been an ornamental favorite in hanging baskets, fountains, and aquaria for more than a century due to its blue-green color, feather-like leaves, oxygenating properties, and cascading pattern of growth (Les 2002, Les and Mehrhoff 1999). Often sold under incorrect names, introductions of this species are usually attributed to the water garden and aquarium trades (Davis 1996, IFAS 2010, Les 2002, Les and Mehroff 1999). It has escaped cultivation through mechanical fragmentation and unintentional plantings, readily taking root. In a Great Lakes regional study, this aquatic plant was found in 25% of the stores surveyed in Michigan and Ontario, near Lake Erie, between 2002 and 2003 (Rixon et al. 2005). Moreover, water garden plants are often left outside to overwinter, which can lead to unintentional escape during spring flooding. The locations of Ontario water gardens identified by 2006 survey respondents suggests that many of these gardens are within the coastal regions of four of the five Great Lakes, though if these were also flood-prone areas was not determined (Marson et al. 2009b).

Myriophyllum aquaticum has a moderate probability of establishment if introduced to the Great Lakes (Confidence level: Moderate).

Parrot feather is a hardy species with broad environmental tolerances (see Ecology above). It occurs as a floating plant in the deep water of nutrient-enriched lakes like the Great Lakes (Washington State Department of Ecology 2011). It is known to tolerate freezing temperatures in California’s Bay area winters (Aiken 1999). However, this plant can be killed by extended periods of frost (WNDR 2011) and so may benefit from warmer winters predicted to result from climate change.

Parrot feather grows vigorously and quickly following invasion in new habitats, forming dense canopies that occupy large amounts of space and block sunlight and oxygen exchange. As a result, this species outcompetes and replaces native flora that might be of more value to fish and wildlife (Stiers et al 2010, WNDR 2011).

Reproduction and dispersal of parrot feather in North America occurs by vegetative fragmentation, which is an effective method for short-range, but not long-range, dispersal (Les and Mehrhoff 1999). Although parrot feather’s natural dispersal potential is limited, this species is widespread outside its native range (Moody and Les 2010). Parrot feather has expanded its range mainly in the southern United States and may be relatively innocuous in the northeast due to a smaller number of occurrences (Hoyer et al. 1996). Nonetheless, this species has survived in southern New England and caused serious local infestations (Becker and Wong 2023, WIDNR 2011). The rapid spread of parrot feather is correlated with its widespread cultivation and the transport of fragments by waterfowl or vehicles. When transport agents are not present, the threat of its escape and establishment depends more on the number of localities where it is grown. Unfortunately, parrot feather remains widely available from sources of cultivated water plants and dealers occasionally plant it intentionally to propagate a local supply (Aiken 1981, Les and Mehrhoff 1999).

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic	Beneficial

The U.S. EPA (2008) predicted that parrot feather could have a high impact and spread rate in the Great Lakes, as it is adaptive to a variety of environments. According to Les and Mehrhoff (1999), rapid spread has been relatively common in this macrophyte’s North American invasion history (Les and 1999).

Dense infestations of parrot feather can rapidly overtake small ponds and sloughs, changing their physical and chemical properties, including impeding water flow, which can result in increased flood duration and intensity. The spread of aquatic nonindigenous plants into a waterbody can also lead to increased rates of evapotranspiration and water loss (Rosa et al. 2009).

Furthermore, parrot feather can dramatically alter ecosystems by shading out algae, pondweeds, and coontail on which waterfowl feed (Ferreira and Moreira 1994, Washington State Department of Ecology 2011). Floating mats of parrot feather have been measured at up to 26 kg of fresh weight in Europe and are capable of reducing the oxygen content (Fonseca 1984 cited in Moreira et al. 1999, Hussner 2008 in Hussner 2009). In Germany, the infestation of these mats created anoxic, shaded conditions in shallow waters, and appeared to be correlated with a decline in native macrophyte diversity (Hussner 2008 in Hussner 2009).

A laboratory study indicated that parrot feather will outcompete native species in high-nutrient sediment (Xie et al. 2010). Furthermore, a mesocosm experiment sugggested that parrot feather has an advantage over algae species when nitrogen levels are elevated (Wersal and Madsen 2011).Stiers et al. (2011) compared Belgian lake sites and found that native species richness was 57% lower in heavily invaded sites relative to uninvaded sites. Parrot feather cover was also negatively correlated with invertebrate species richness and abundance, possibly due to dense mats of parrot feather reducing oxygen levels(Stiers et al. 2011). Utricularia vulgaris (rare in Belgium, native to the Great Lakes region) and Hydrocharis morsus-ranae (a vulnerable IUCN Red List species in Belgium and invasive in the Great Lakes) were absent in heavily invaded sites but present in semi-invaded sites (Steirs et al. 2011).

Parrot feather can also alter the cycling of heavy metals in aquatic systems. Cardwell et al. (2002) found that parrot feather accumulated the highest overall levels of metals (zinc, cadmium, copper, and lead) in its tissues of all 15 aquatic plants that underwent testing. The consumption of parrot feather by grazers could increase the bioaccumulation of heavy metals in the food web.

Myriophyllum aquaticum has the potential for high socio-economic impact if introduced to the Great Lakes.

Parrot feather infestations have been reported in both natural and man-made water bodies, including lakes, ponds, canals, drainage and irrigation ditches, and lagoons. Plants and floating mats of vegetation are sometimes uprooted, choking waterways, inhibiting navigation, and potentially blocking pumps or drainage (Engineer Research and Development Center 2007, Sheppard et al. 2006). Dense growth can also diminish the recreational value and seriously affect the perceived aesthetic qualities of infested waterways (Banfield 2008, Washington State Department of Ecology 2011).

Parrot feather monocultures provide prime mosquito habitat; higher parrot feather density has been correlated with higher mosquito egg and larval abundance (Orr and Resh 1992), which may lead to increased prevalence of mosquito-born diseases.

One account by South African farmers also reported that tobacco crops gained a red tint (reducing the sale value of the crop) when irrigated with water from an area colonized by parrot feather roots (Cilliers 1999).

Myriophyllum aquaticum has the potential for moderate benefits if introduced to the Great Lakes.

Assessment protocols have been developed using parrot feather as a primary indicator species of sediment toxicity in potentially polluted areas (Feiler et al. 2004, Knauer et al. 2008).

Parrot feather is an important species in the aquarium trade and can be found in shops in both the American and Canadian Great Lakes regions (Marson et al. 2009a, Rixon et al. 2005). It is reportedly sold as an “oxygenating plant” in Europe (Sheppard et al. 2006).

Parrot feather may provide cover for some aquatic organisms (Washington State Department of Ecology 2011). Parker et al. (2007) found that beavers (Castor canadensis) in Georgia fed on M. aquaticum to the extent that invasive populations were reduced, although no strong preference for this plant species over others was documented.

Parrot feather could be used for nitrogen and phosphorus remediation (e.g., in a constructed wetland remediating nutrient runoff), but Polomski et al. (2009) found that other invasive macrophytes (Eichhornia crassipes and Pistia stratiotes) had equal or greater uptake efficiency levels relative to parrot feather. Parrot feather can also aid in environmental remediation of soil and water contaminated with chlorinated solvents, trinitrotoluene (TNT), and other nitrogenated explosive/aromatic compounds (Medina et al. 2000, Nwoko 2010).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Although parrot feather is not considered a widespread nuisance, once it becomes established in an area it is very difficult to control. Several methods, including chemical, mechanical, and biological control, have been evaluated with mixed results. Chemical and mechanical methods can provide short to medium term control of parrot feather. Herbicides have been used most often for control of parrot feather and results have been dependent upon herbicide choice. Mechanical methods are much less documented; however, their use may facilitate regrowth and further spread of parrot feather. Biological control has been evaluated; however, there are no viable options available in the United States. The most effective method to avoid infestations is likely to prevent unintentional release from water gardens.

Chemical
Parrot feather’s waxy cuticle on stems and leaves can only be penetrated with a wetting agent, making chemical control challenging—the weight of spraying may cause the plants to sink in the water, which can wash the herbicide off before it can take effect. Nevertheless, the most successful herbicides currently used for parrot feather control include those that can be applied to foliage, such as 2,4-D, triclopyr, diquat, carfentrazone, imazapyr, and imazamox. The use of 2,4-D and triclopyr as a foliar applications have resulted in consistent control of parrot feather (Hofstra 2006; Moreira et al. 1999). Glyphosate is generally not recommended as this herbicide only kills emergent shoots and plants often regrow in greater densities (Moreira et al. 1999). Diquat is a contact herbicide that will kill the vegetation it comes in contact with, but significant regrowth is common (Westerdahl and Getsinger 1988). Carfentrazone-ethyl will not control parrot feather as a foliar application (Richardson et al. 2008). The use of imazapyr and imazamox have been evaluated on small infestations with excellent to fair results, respectively (Wersal and Madsen 2007).

Subsurface herbicide applications do not result in increased control relative to foliar applications (Wersal and Madsen 2010). Carfentrazone-ethyl will not control parrot feather and is not recommended as a stand-alone treatment (Glomski et al. 2006; Gray et al. 2007). However, when carfentrazone-ethyl was combined with 2,4-D it resulted in excellent control of small parrot feather populations (Gray et al. 2007).

Multiple applications are often necessary to completely control parrot feather. The effectiveness of herbicide applications will be site specific and depend upon the environmental conditions at the time of application.

Physical

Cutting plants will only increase spread, as parrot feather reproduces vegetatively. Hand pulling and harvesting may offer temporary control, however this approach is very labor intensive as dense mats are heavy and difficult to haul out of the water (Guillarmod 1977). Raking and chaining (long chains of sharp blades pulled by tractors) may not be feasible due to the rapid biomass production of parrot feather; moreover, dense mats may damage equipment. Sebbatini et al. (1998) reported that parrot feather was tolerant to mechanical disturbance (raking and chaining) and the repeated application of mechanical techniques favored parrot feather dominance in canals. Care must be taken to remove all plant parts (emergent shoots, submersed shoots, and roots), as well as fragments created by the removal, or re-growth will occur.

Water drawdown may be a viable option for parrot feather control, but the effectiveness of this approach has yet to be determined. To be successful, a drawdown would have to be sustained long enough to completely dry the soil, as parrot feather can and will survive in moist soil. Dredging is generally very expensive and not feasible for most management situations.

Biological
Currently, the grass carp (Ctenopharyngodon idella) and a leaf feeding beetle (Lysathia spp.) have been evaluated for control of parrot feather infestations. Grass carp are not recommended for parrot feather control as fish generally avoid eating this plant due to its high tannin content (Catarino et al. 1997; WSDE 2003 in Mabulu 2005; Pine and Anderson 1991). The leaf-feeding beetle showed some promise in South Africa by significantly reducing emergent shoot biomass (Cilliers 1999; Mabulu pers. comm. 2004 in Mabulu 2005); however, this agent is not approved for use in the United States. Existing evidence supports that beaver (Castor canadensis) provides some control of M. aquaticum in the Gumby Swampland (Georgia); when beavers were excluded at certain sites, M. aquaticum abundance increased nearly 8-fold and accounted for up to 95% of the increased vegetative growth in the exclusions (Parker et al. 2007).

Cultural Control & Prevention of Spread
Parrot feather is a common component of aquatic landscaping because of its aesthetic appearance and ease of cultivation (Sutton 1985). Aiken (1981) reported observations of aquarium plant providers in the San Francisco Bay area placing of parrot feather plants into local waterways to have a convenient source of saleable material. The ease of cultivation and attractiveness as a pond plant has aided in its escape and subsequent colonization of natural areas.

Cultural prevention approaches are the best way to avoid parrot feather infestations, as this plant is almost exclusively spread by human means (e.g., propeller or fishing gear entanglement, ornamental release) (Guillarmod 1977). This species is also likely to be resilient to water level fluctuations resulting from climate change (Huessner et al. 2009).

Ultimately, to prevent the future introduction and spread of parrot feather into new areas it must be prohibited from sale by the water garden and aquaculture industries.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.