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Crassula helmsii (aquatic plant, succulent) |
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Management Information
Preventative measures: Several measures can be taken to prevent the establishment of Crassula helmsii. Its sale should be restricted in gardens centers, supermarkets, aquarists, and other retailers. Public awareness campaigns should provide information on the environmental and economic impacts of C. helmsii with focus on key groups associated with its import and sale. Removal of domestic plantings in ponds and aquariums and replacement with native species should be encouraged. If established, mesh netting can be used to prevent the spread of C. helmsii to uninvaded bodies of water (Kelly & Maguire, 2009; Berwick, 2009).
Physical removal: Hand pulling of Crassula helmsii is considered to be ineffective as regrowth is very rapid. Mechanical removal of C. helmsii is not recommended because small fragments released into the water column can travel downstream to colonize new sites or recolonize the treated area. Dredging material can be effective for emergent and submerged material as C. helmsii is shallow rooted however it could potentially damage the natural seed bank. Creating shaded areas by covering with black plastic of UV sheeting for up to 6 months has been successful and is very effective when combined with herbicide treatment. Burial with more than 20 cm of soil can result in 100% mortality but is labor intensive and causes much disturbance (Berwick, 2009; CEH, 2004; Bridge, 2005).
Biological control: Grass carp (Ctenopharyngodon idella) feed on C. helmsii, although it is not their preferred food source. A large scale trial confirmed the some control of C. helmsii accompanied by an increase in macrophyte species diversity. However, C. idella are reported to not survive well in waters with a high fluctuations of dissolved oxygen, which is associated with dense C. helmsii populations. Additionally C. idella is also an invasive species that may establish and cause a ecological impacts of its own (Berwick, 2009; Dawson & Warman, 1987). Chrysomelid and curculionid beetles have also been suggested as potential biological controls (Gassman et al, 2006).
Chemical control: Diquat alginate (Midstream) has been found to be the most effective chemical control of C. helmsii with a 95% kill rate and is the only chemical that can effectively kills submerged plants. However, it has been removed from the EU list of acceptable herbicides and has been determined unsafe for aquatic use. Dichlobenil (Casoron G or Midstream GSR) is also recommended but it too will soon be withdrawn from the market. Glyphosate (Roundup biactive) has a 50% kill rate and is the recommended method of treating emergent C. helmsii. Glysophate is most successful when treating before and after mechanical removal or on a new infestation and can be combined with adjuvant TopFilm to increase effectiveness (Berwick, 2009; CEH, 2004; Kelly & Maguire, 2009).The use of Waipuna hot foam, a biodegradable organic compound of coconut and corn sugar which breaks down the cellular structure of the plant, has a 50% kill rate, but primarily kills only the top layers of the plant. Waipuna foam has several advantages over herbicides. It is not weather dependent and can be used in breezy conditions and light rain. Unlike herbicide treatments there is no requirement for special safety equipment. The foam can be applied with accuracy and without damage to adjacent plants. It is also non-toxic to other wildlife (Berwick, 2009; Bridge, 2005).
Integrated management: The combination of methods physical removal, shading, and herbicide treatment has been found to be the most effective means for controlling C helmsii populations. The spraying of plant material with herbicide followed by covering with black or UV sheeting or physical removal are both effective and may be repeated until eradication is obtained (CEH, 2004; Kelly & Maguire, 2009).
Location Specific Management InformationEngland
A management study conducted in the Lound Lakes tested several methods of controlling Crassula helmsii. Although none appear to be capable of complete eradication, control with glyphosate and Waipuna hot foam, a biodegradable organic compound of coconut and corn sugar which breaks down the cellular structure of the C. helmsii, has been used to reduce populations which threaten pillwort (Pilularia globulifera). Researchers also prevent its spread by installing mesh netting around invaded bodies of water (Berwick, 2009).
Glyposate, Waipuna hot foam, and burial were used in a similar management project in the Old Moor Royal Society for the Protection of Birds Reserve. Glyphosate and Waipuna hot foam caused 50% mortality. Burial yielded 100% mortality but was very labor intensive and caused significant disturbance (Bridge, 2005). The use of Reglone (Diquat) was employed to control C. helmsii in at the Dungeness RSPB Reserve, Kent England and achieved 70% mortality. Follow up spraying was required to manage re-growth. Eradication was not possible but manageable control was obtained (Gomes, 2005).
In The Lodge Royal Society for the Protection of Birds (RSPB) shading using black polythene was conducted on C. helmsii populations for six months. The treated population was killed but recolonization by outlying, untreated plants quickly resulted (Wilton-Jones, 2005). Florida (USA)
Crasulla helmsii is a class 1 prohibited aquatic plant in Florida (USDA-NRCS, undated). Germany
No management for Crassula helmsii has been carried out in Germany yet. Ireland
An Invasive Species Action Plan has been developed for Crassula helmsii in Ireland. Preventative measures include restriction of its sale and planting and increase of public awareness about its environmental and economic impacts. Management plans include formulating a comprehensive baseline distribution followed by prioritized eradication efforts with a goal of complete eradication. These efforts will consist of integrated use of cutting, shading, and spraying herbicide glyosophate (Kelly & Maguire, 2009). North Carolina
Crasulla helmsii is a class A noxious weed in North Carolina (USDA-NRCS, undated). Scotland
Crassula helmsii meets criterion 2 of the Scotland's Species Action Framework as an invasive non-native species which presents a great risk to biodiversity. It has also recently been added to Schedule 9 of the Wildlife and Countryside Act (1981), as amended, making it an offence to deliberately introduce this species to the wild. Plantlife Scotland have produced a leaflet highlighting species that are a problem when planting out ponds, including C. helmsii. It is also included in the Plantlife Flora Guardian programme for Scotland, using volunteers to record its spread (SNH, 2009). Washington
Crasulla helmsii is under wetland and aquatic weed quarantine in Washington (USDA-NRCS, undated).
Management Resources/Links
1. Berwick, Holly. 2009. Crassula helmsii at Lound Lakes Management Options. Broads Authority - The broads, a member of the National Park family. Essex and Suffolk Water. 5. Dawson, F. H. 1996. Crassula helmsii: Attempts at elimination using herbicides. Hydrobiologia. 340(1-3). 1996. 241-245. 8. Gassmann, Andre, Cock, Matthew J. W., Shaw, Richard, Evans, Harry C. 2006. The potential for biological control of invasive alien aquatic weeds in Europe: a review. Hydrobiologia. 570 OCT 15 2006. 217-222. 11. Linton, S & R. Goulder., 2000. Botanical conservation Value related to origin and management of ponds Aquatic Conser 6: Mar. Freshw. Ecosyst. 10: 77–91 (2000) 12. Manchester Sarah, J & James M. Bullock, 2000. The impacts of non-native species on UK biodiversity and the effectiveness of control. Journal of Applied Ecology 2000, 37, 845±864 14. Sheppard, A.W.; R.H. Shaw & R. Sforza., 2005. Top 20 environmental weeds for classical biological control in Europe: a review of opportunities, regulations and other barriers to adoption. Weed Research 2006 46, 93–117 17. Wilton-Jones, G. 2005. Control of New Zealand pygmyweed Crassula helmsii by covering with black polythene at The Lodge RSPB Reserve, Bedfordshire, England. Conservation Evidence (2005) 2, 63 Results Page: 1
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