Regulations
Possession of live parrot feather is prohibited in Illinois, Michigan, and Wisconsin; regulated in Minnesota (GLPNS 2008, IISG 2011, WIDNR 2011). Note: Check federal, state/provincial, and local regulations for the most up-to-date information.
Control
Preface: 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.