Cabomba (Portuguese-Brazil), Carolina water-shield, Fanwort, Fish grass, Green Cabomba, Washington grass, Washington-plant

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

Environmental	Socioeconomic	Beneficial

Cabomba caroliniana has formed monocultures in Kasshabog Lake, Ontario (Hosgsden et al. 2007 Wilson et al. 2007). The main difference between native macrophyte beds and beds of C. caroliniana in this location is significantly reduced light penetration (Hogsden et al. 2007).

Dense stands of C. caroliniana disrupts fish habitat and replaces native foods sources; which can alter predator/prey relationships among the fish populations (ENSR International 2005, OISAP 2005, PA DCNR 2011, Program 2013).

Large infestations can affect the oxygen concentrations, pH, and organic content of the nearby water and soil (ENSR International 2005, PADCNR 2011). Furthermore, dieback and decomposition could alter nutrient cycling, potentially reducing dissolved oxygen levels and increasing manganese levels (Wilson et al. 2007).

Potential:
After an analysis of invasive species by the U.S. Army Corps of Engineers, the predicted expansion of C. caroliniana was so extensive that this species could pose a severe threat to ecosystems in Minnesota (Madsen 1999).  Warmer winter temperatures and lower water levels may aide in the continued northward expansion of C. caroliniana (Hudon and Carignan 2008).

Cabomba caroliniana mats can trap detritus and increase sedimentation which could alter the hydrology or even clog freshwater streams and drainage canals (ENSR International 2005, Forest Health Staff 2006, U.S. EPA 2008). 

Morrison and Hay (2011) found that in response to direct feeding activity, C. caroliniana is capable of inducing a chemical defense to suppress herbivory.  Cabomba caroliniana extracts also inhibited growth of 5 different microbes by 20-90%, suggesting that C. caroliniana has an anti-microbial defense at feeding scar sites (Morrison and Hay 2011). Due to its ability to induce a chemical defense, the establishment of C. caroliniana could have implications for herbivore fitness and trophic interactions, as well as important microbial activities (Morrison and Hay 2011).

Cabomba caroliniana has a moderate socio-economic impact in the Great Lakes.
Realized:
Cabomba caroliniana's dense mass of underwater leaves and stems provide a tangling hazard for swimmers, boats, fishing lines, and other recreational water users (Ensbey and Oosterhout 2010, Schooler et al. 2006, Wilson et al. 2007). Infestations of this species can cause the water to become stagnant will can cause it to become dark and foul-smelling; ultimately reducing the aesthetic value (Ensbey and Oosterhout 2010). Limitations on water uses can negatively impact real estate values (ENSR International 2005).

Dense mats of C. caroliniana clog streams, drainage canals, and drinking water intakes and interferes with agricultural water uses (WI DNR 2012). Cabomba caroliniana is capable of significantly reducing water storage capacity and tainting/discoloring drinking water supplies, potentially increasing water treatment costs (Lui et al. 2010).

At Kasshabog Lake, Ontario, C. caroliniana has become a nuisance for residents and recreational users, discouraging swimming and boating and reportedly affecting the aesthetic value of shoreline property (Wilson et al. 2007).  

Potential:
If C. caroliniana spreads from Kasshabog Lake to the Trent-Severn Waterway and Great Lakes system, power generation, aquaculture, and other water-based industries could be impacted (Wilson et al. 2007). For instance, Wilson et al. (2007) predicted that C. caroliniana establishment could be detrimental to Canadian populations of wild rice (Zizania palustris L.), a commercially important plant with similar ecological requirements to C. caroliniana.

An estimated $500,000 a year was spent on control of C. caroliniana in Australia as of 2003 (ADEH 2003, Schooler et al. 2006).

Current research on the beneficial effects of Cabomba caroliniana in the Great Lakes is inadequate to support proper assessment.
Realized:
Because of its attractive appearance and its ability to grow quickly, C. caroliniana has been a commercially-important plant in the aquarium trade worldwide (Wilson et al. 2007). Rixon et al. (2005) documented its presence in 20% of investigated aquarium stores in the Great Lakes region, while Cohen et al. (2007) reported C. caroliniana as one of the top 10 plants in the Montreal aquarium trade. Additionally, C. caroliniana was one of the most popular aquatic plants among surveyed aquarium owners in Canada (Marson et al. 2009). However, C. caroliniana is also restricted or prohibited in some Great Lakes states (GLPANS 2008).

While the composition of algae and macroinvertebrate communities were similar between native macrophyte and C. caroliniana beds in Kasshabog Lake, both were more abundant in C. caroliniana beds, potentially because its growth morphology provided more favorable structure for habitat (Hogsden et al. 2007).

Potential:
Relative to native macrophytes, its ecological value as a source of food or habitat for wildlife is unclear (Wilson et al. 2007). However, in some instances C. caroliniana may provide cover for macroinvertbrates and spawning ground for fish (Hamel 2013, Tilt 2013).

Cabomba caroliniana is capable of sequestering lead and may be useful in reclamation efforts (Mikulyuk and Nault 2011).

Preliminary research indicated that C. caroliniana plant matter that is mechanically harvested for control purposes could be anaerobically digested to produce and harness methane-rich gas for energy purposes (O'Sullivan et al. 2010).

The Great Lakes Life & Wildlife Commission have not found C. caroliniana in their ceded territories, but recommended immediate control upon detection (Falck and Garske 2003).

Cabomba caroliniana is restricted in Ontario (regulatory amendments to Ontario Regulation 354/16 under the Invasive Species Act, 2015).

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

Control
Biological
When fed on my crayfish and snails, C. caroliniana induces a chemical defense mechanism deter both herbivores and microbes that typically attack plants via openings left by herbivores (Morrison and Hay 2011).

Grass carp, Ctenopharyngodon idella, will eat C. caroliniana, but it is not their preferred food source.  Diploid (fertile) grass carp are illegal for use in some states, such as Minnesota (MN DNR 2013a). The use of certified triploid (sterile) grass carp is allowed is New York and Pennsylvania, with the correct permits (NY DEC 2013, Shiels and Hartle n.d.)

Chemical defense also indicates that the use of biocontrol agents on invasive populations of C. caroliniana may not be a viable approach (Morrison and Hay 2011).

Physical
Cabomba caroliniana becomes brittle late in the growing season. Physical control efforts should not be tried during this time because broken pieces can develop into new plants (IISCTC 2007).

Physical cutting and removal of C. caroliniana is most effective on large infestations in closed water bodies (ADEH 2003). In areas of sufficient size and depth, this can be done with floating mechanical (CSIRO Entomology 2011). However, given the low probability of removing every plant fragment, this method is likely to only provide nuisance relief for a few weeks (ADEH 2003). Efficacy can be improved by using tools such as a venturi dredge, which acts like a vacuum cleaner to C. caroliniana fanwort fragments and the root ball (WI DNR 2012). 

Water-level drawdowns have reduced growth of C. caroliniana populations in some areas in southern Wisconsin (WI DNR 2012). Extreme drying, in which the root ball dries completely, is needed or the plant will return (Forest Health Staff 2006, IISCTC 2007).

Ensuring wash-downs of boats, trailers, and other equipment can reduce the spread of Carolina fanwort
(IISCTC 2007).

Chemical
Precise application of appropriate herbicides to submerged C. caroliniana can be problematic and should be done with great care to avoid desired species (ADEH 2003).

Herbicides containing endothall or fluridone have been effective in controlling C. caroliniana (ADEH 2003, Forest Health Staff 2006). Carolina fanwort has also been reported to be sensitive to 2,4-D (Wilson et al. 1997).

In laboratory tests, the application of diquat and flumioxazin (separately) resulted in a greater than 50% reduction in photosynthesis of C. caroliniana, however, these herbicides has not been tested in the field (Bultemeier et al. 2009).

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