Pacific Island Ecosystems at Risk (PIER)


Salvinia molesta


RISK ASSESSMENT RESULTS: High risk, score: 29


Australian/New Zealand Weed Risk Assessment adapted for Hawai‘i.

Research directed by C. Daehler (UH Botany) with funding from the Kaulunani Urban Forestry Program and US Forest Service

Information on Risk Assessments
Original risk assessment

Salvinia molesta (giant salvinia, aquatic watermoss, kariba weed)

Answer

1.01

Is the species highly domesticated?

y=-3, n=0

n

1.02

Has the species become naturalized where grown?

y=-1, n=-1

y

1.03

Does the species have weedy races?

y=-1, n=-1

n

2.01

Species suited to tropical or subtropical climate(s) (0-low; 1-intermediate; 2-high) – If island is primarily wet habitat, then substitute “wet tropical” for “tropical or subtropical”

See Append 2

2

2.02

Quality of climate match data (0-low; 1-intermediate; 2-high) see appendix 2

2

2.03

Broad climate suitability (environmental versatility)

y=1, n=0

y

2.04

Native or naturalized in regions with tropical or subtropical climates

y=1, n=0

y

2.05

Does the species have a history of repeated introductions outside its natural range? y=-2

?=-1, n=0

y

3.01

Naturalized beyond native range y = 1*multiplier (see Append 2), n= question 2.05

y

3.02

Garden/amenity/disturbance weed y = 1*multiplier (see Append 2)

n=0

y

3.03

Agricultural/forestry/horticultural weed y = 2*multiplier (see Append 2)

n=0

y

3.04

Environmental weed y = 2*multiplier (see Append 2)

n=0

y

3.05

Congeneric weed y = 1*multiplier (see Append 2)

n=0

y

4.01

Produces spines, thorns or burrs

y=1, n=0

n

4.02

Allelopathic

y=1, n=0

n

4.03

Parasitic

y=1, n=0

n

4.04

Unpalatable to grazing animals

y=1, n=-1

n

4.05

Toxic to animals

y=1, n=0

n

4.06

Host for recognized pests and pathogens

y=1, n=0

n

4.07

Causes allergies or is otherwise toxic to humans

y=1, n=0

n

4.08

Creates a fire hazard in natural ecosystems

y=1, n=0

n

4.09

Is a shade tolerant plant at some stage of its life cycle

y=1, n=0

y

4.1

Tolerates a wide range of soil conditions (or limestone conditions if not a volcanic island)

y=1, n=0

4.11

Climbing or smothering growth habit

y=1, n=0

y

4.12

Forms dense thickets

y=1, n=0

y

5.01

Aquatic

y=5, n=0

y

5.02

Grass

y=1, n=0

n

5.03

Nitrogen fixing woody plant

y=1, n=0

n

5.04

Geophyte (herbaceous with underground storage organs -- bulbs, corms, or tubers)

y=1, n=0

n

6.01

Evidence of substantial reproductive failure in native habitat

y=1, n=0

n

6.02

Produces viable seed.

y=1, n=-1

n

6.03

Hybridizes naturally

y=1, n=-1

6.04

Self-compatible or apomictic

y=1, n=-1

6.05

Requires specialist pollinators

y=-1, n=0

n

6.06

Reproduction by vegetative fragmentation

y=1, n=-1

y

6.07

Minimum generative time (years) 1 year = 1, 2 or 3 years = 0, 4+ years = -1

See left

1

7.01

Propagules likely to be dispersed unintentionally (plants growing in heavily trafficked areas)

y=1, n=-1

y

7.02

Propagules dispersed intentionally by people

y=1, n=-1

y

7.03

Propagules likely to disperse as a produce contaminant

y=1, n=-1

y

7.04

Propagules adapted to wind dispersal

y=1, n=-1

y

7.05

Propagules water dispersed

y=1, n=-1

y

7.06

Propagules bird dispersed

y=1, n=-1

n

7.07

Propagules dispersed by other animals (externally)

y=1, n=-1

y

7.08

Propagules survive passage through the gut

y=1, n=-1

n

8.01

Prolific seed production (>1000/m2)

y=1, n=-1

n

8.02

Evidence that a persistent propagule bank is formed (>1 yr)

y=1, n=-1

y

8.03

Well controlled by herbicides

y=-1, n=1

y

8.04

Tolerates, or benefits from, mutilation, cultivation, or fire

y=1, n=-1

y

8.05

Effective natural enemies present locally (e.g. introduced biocontrol agents)

y=-1, n=1

n

Total score:

29

Supporting data:

Source

Notes

1.01

No evidence

1.02

It is a serious weed in New Guinea, Australia, Mauritius, Africa, India, Sri Lanka, Ceylon, New Zealand, and elsewhere. In the US it has been observed in South Carolina (eradicated), Texas, and Louisiana.

http://tncweeds.ucdavis.edu/alert/alrtsalv.html

1.03

No evidence

2.01

Salvinia molesta is native to southeastern Brazil.

http://tncweeds.ucdavis.edu/alert/alrtsalv.html

2.02

S. molesta establishes itself extremely successfully and rapidly in tropical, sub-tropical, and warm temperate areas of the world. It is found in ditches, ponds, lakes, slow moving rivers, and irrigation canals.  

http://www.wapms.org/plants/salvinia.html

2.03

(1)Wide latitudinal range. It is native of Southeastern Brazil and grows was found to grow in coastal North Carolina. - 'The United State Geological Service anticipates that S. molesta could potentially establish within Zone 8 of the USDA Plant Hardiness Map. Giant salvinia has successfully overwintered along coastal North Carolina at a latitude of 34.4 degrees north (USDA Zone 8) and in Texas at 33 degrees north (USDA Zone 7b). (2)It is very adaptable and will survive in many climates, although low temperatures will reduce its growth rate. It can withstand the occasional frost

(1)http://www.wapms.org/plants/salvinia.html (2)http://www.agric.nsw.gov.au/reader/5381

2.04

(1)It is a serious weed in New Guinea, Australia, Mauritius, Africa, India, Sri Lanka, Ceylon, New Zealand, and elsewhere. In the US it has been observed in South Carolina (eradicated), Texas, and Louisiana. (2)Salvinia molesta is native to southeastern Brazil.

(1)http://tncweeds.ucdavis.edu/alert/alrtsalv.html (2)http://tncweeds.ucdavis.edu/alert/alrtsalv.html

2.05

Salvinia molesta has been spread to many part of the world, perhaps initially by the aquarium and garden-pond trades.

http://tncweeds.ucdavis.edu/alert/alrtsalv.html

3.01

(1)It is a serious weed in New Guinea, Australia, Mauritius, Africa, India, Sri Lanka, Ceylon, New Zealand, and elsewhere. In the US it has been observed in South Carolina (eradicated), Texas, and Louisiana. (2)Salvinia molesta is native to southeastern Brazil.

(1)http://tncweeds.ucdavis.edu/alert/alrtsalv.html (2)http://tncweeds.ucdavis.edu/alert/alrtsalv.html

3.02

Mats impede boating, fishing, and swimming and clog water intakes for irrigation and electrical generation.

http://www.sdafs.org/reservor/news/releases/salvinia.htm

3.03

Giant salvinia clogs water intakes to interfere with agricultural irrigation and electrical generation. Many infested farm ponds in Texas lie on creeks that drain tributaries heavily depended on for agricultural irrigation.

http://salvinia.er.usgs.gov/html/identification.html

3.04

(1)This plant has been detected in several bodies of water near the Texas/Louisiana border, and along the Colorado River. It is extremely invasive--any new infestations must be reported and eradicated immediately. A Task Force has been created to deal with the lower Colorado River infestation. The plant is federally prohibited in the US, and is therefore illegal to sell or possess! (2)Giant salvinia has the potential to alter aquatic ecosystems in several ways. Rapidly expanding populations can overgrow and replace native plants. Resulting dense surface cover prevents light and atmospheric oxygen from entering the water. Meanwhile, decomposing material drops to the bottom, greatly consuming dissolved oxygen needed by fish and other aquatic life (3)A rapidly expanding infestation of Salvinia molesta at Enchanted Lakeclick to open Enchanted Lake images, Kailua, on the island of Oahu (Robert Bourke, Oceanit Laboratories), was feared to threaten the nesting habitat of three endangered water birds, the Hawa

(1)http://tncweeds.ucdavis.edu/alert/alrtsalv.html (2)http://salvinia.er.usgs.gov/html/identification.html (3)http://salvinia.er.usgs.gov/html/distribution_map.html

3.05

Four species of Salvinia (S. auriculata, S. biloba, S. herzogii, and S. molesta) share the feature of egg beater-like hairs. All can be expected to be aggressive weeds and all four are prohibited as Federal Noxious Weeds. Of the four with egg beater-like hairs, only S. molesta is presently being found in the United States.

http://agriculture.state.az.us/PSD/giant_sal1.htm

4.01

No evidence

http://salvinia.er.usgs.gov/html/identification.html

4.02

No evidence

4.03

No evidence

4.04

(1)sheep forage? (2)Owing to its high nitrogen content (CP) of 20-33% per gram dry weight, Salvinia is used as livestock forage and is fed to swine, poultry

(1)www.bath.ac.uk/~en8cdy/P2_Tech_01.doc (2) Lopez, F.S.S.Tan, B.C. 1986 Economic potentials of Salvinia molesta Mitchell. Philippine Journal of Crop Science (Philippines). 11(Supplement No. 1):56.

4.05

No evidence

4.06

(1)Patches of water-soaked lesions were observed on the pinnules and rachises of screenhouse-grown S. molesta plants in Florida, USA. Mycelia spread centrifugally from these patches and caused diseased plants to disintegrate and sink. Brown-to-black sclerotia were formed on and around the disintegrated plants. A fungus was consistently isolated from symptomatic tissues of S. molesta plants. The fungus was identified as Rhizoctonia solani.
(2)R. solani is a very common soilborne pathogen with a great diversity of host plants

(1) Rayachhetry, M. B.; Center, T. R.; Center, T. D.; Tipping, P.; Pratt, P. D.; Van, T. K. 2002. First report of the pathogenicity of Rhizoctonia solani on Salvinia molesta and S. minima in Florida. Plant Disease. Vol.86, No.7, p.813. (2)http://www.cals.ncsu.edu/course/pp728/Rhizoctonia/Rhizoctonia.html

4.07

No evidence

4.08

Probably not - an aquatic species.

4.09

'Under shade, fresh wt. increase was highest in June-July, while under full sunlight, Aug.-Sept. growth was best.

Rani, V. U.; Bhambie, S. . 1983. A study on the growth of Salvinia molesta Mitchell in relation to light and temperature. Aquatic Botany. Vol.17, No.2. 119-124.

4.1

Soil conditions not relevant - aquatic species. Regarding water pH - does not seem to be tolerant of high salinity. 'Salvinia molesta is strictly a freshwater species, not tolerating brackish or marine environments. In experimental trials, salinity above 7 parts per thousand (ppt) retarded growth and damaged plant tissues. Higher salt concentrations proved lethal. Plants maintained at 11 ppt were killed after 20 hours exposure. At 20 ppt, mortality resulted in less than 1.5 hours. Full strength seawater (34 ppt) killed plants in 30 minutes.'

http://salvinia.er.usgs.gov/html/identification.html

4.11

It is not a climber/vine but seems to have a smothering habit. - 'Mats of salvinia have been recorded to be as large as 96 square miles in area and up to 3 feet deep. These mats can block all sunlight from penetrating the infested water body thus eliminating all of the native submerged vegetation that is so important to the fish. Additionally, as the plants die and decay they can cause a decrease in dissolved oxygen in the water body. Both of these actions will severely reduce the habitat available for fish within the water body.'

http://www.saj.usace.army.mil/conops/apc/Salvinia.html

4.12

Mats of salvinia have been recorded to be as large as 96 square miles in area and up to 3 feet deep. These mats can block all sunlight from penetrating the infested water body thus eliminating all of the native submerged vegetation that is so important to the fish. Additionally, as the plants die and decay they can cause a decrease in dissolved oxygen in the water body. Both of these actions will severely reduce the habitat available for fish within the water body.'

http://www.saj.usace.army.mil/conops/apc/Salvinia.html

5.01

Family-Salviniaceae; Division-Polypodiophyta (Pteridophyta), true ferns.

Salvinia represents a single genus in this family of remarkably adapted water ferns. Floating, rootless aquatic fern.

http://salvinia.er.usgs.gov/html/identification.html

5.02

5.03

5.04

6.01

Mature plants can produce large quantities of sporocarps, which are actually outer sacs that contain numerous sporangia. However, the sporangial sacs are usually empty of microscopic spores or with only a few deformed remnants. Being a pentaploid species, Salvinia molesta demonstrates irregularities during meiosis that prevent spore formation and result in functionally sterile plants

http://salvinia.er.usgs.gov/html/identification.html

6.02

Mature plants can produce large quantities of sporocarps, which are actually outer sacs that contain numerous sporangia. However, the sporangial sacs are usually empty of microscopic spores or with only a few deformed remnants. Being a pentaploid species, Salvinia molesta demonstrates irregularities during meiosis that prevent spore formation and result in functionally sterile plants

http://salvinia.er.usgs.gov/html/identification.html

6.03

'Details of the karyotype of Salvinia molesta (2n = 45) were studied for the first time. The somatic chromosomes range between 1.6 mu m and 4.1 mu m in length. Out of the 45 chromosomes 29 are median and 14 are submedian. Two chromosomes have centromeres at the terminal regions. Five chromosomes are satellited. The chromosomes fall into 18 groups, nine groups each of three chromosomes (genome A) and nine groups, each of two chromosomes (genome B). On the basis of the above and evidence from multivalent association during meiosis, it is suggested that S. molesta is a pentaploid hybrid of a hexaploid and a tetraploid species. Study on the cytology of the putative parents would be valuable in throwing further light on the hybridity of this species.

Kuriachan, P. I. 1979. Interspecific origin of Salvinia molesta Mitchell evidence from karyotype. Indian Journal of Botany. Vol.2, No.1, pp.51-54.

6.04

6.05

Not applicable - a pteridophyte.

6.06

Salvinia molesta effectively reproduces through vegetative means. Stems fragment spontaneously as plants mature. New branches develop from apical and lateral buds. Each node harbors up to five serial lateral buds (Lemon and Posluszny 1997), adding to the high potential for growth and dormancy.

http://salvinia.er.usgs.gov/html/identification.html

6.07

[Since the plant does not reproduce by sexual means I have considered the doubling time as minimum generative time] - 'One reason is that S. molesta can double its numbers every 2.2 days under ideal conditions. If you consider this doubling rate and add just one plant to a water body, you will have over 8,000 plants within the first month. In a large water body, this amount may not be noticed, but after 2 months you will have more than 67,000,000 plants and by 4 months after the initial introduction, there could be over 4,500,000,000,000,000 plants!'

http://www.saj.usace.army.mil/conops/apc/Salvinia.html

7.01

(1) boat propellers,docking lines, fishing gear, and other equipment (2)Plants can be carried overland on anything entering infested waters.

(1)http://pi.cdfa.ca.gov/weedInfo/SALVINIA2.html (2)http://www.sdafs.org/reservor/news/releases/salvinia.htm

7.02

Probably yes - it is grown in home aquariums and koi ponds. 'Salvinia molesta was most likely introduced through the aquarium and landscaping trades. ...One possible route of infestation is that an individual may dump it in a nearby canal, pond, ditch or lake when it overgrows the home aquaria or koi ponds.'

http://www.saj.usace.army.mil/conops/apc/Salvinia.html

7.03

Contaminants in other plant shipments that have been introduced for the aquarium trade.

http://netenergy.dpie.gov.au/content/output.cfm?ObjectID=D2C48F86-BA1A-11A1-A2200060B0A03950

7.04

dispersed by wind and water.

http://www.hear.org/pier/samol.htm

7.05

dispersed by wind and water.

http://www.hear.org/pier/samol.htm

7.06

[not as food]

7.07

Probably yes- if pieces of the plant get caught in the feet of water birds that visit an uninfested waterbody.

7.08

8.01

(1)Sporocarps in long straight secund chains, hairy, about 1 mm in diameter, containing mostly empty sporangia." (2)the sporangial sacs are usually empty of microscopic spores or with only a few deformed remnants. Being a pentaploid species, Salvinia molesta demonstrates irregularities during meiosis that prevent spore formation and result in functionally sterile plants

(1)http://www.hear.org/pier/samol.htm (2)http://salvinia.er.usgs.gov/html/identification.html

8.02

(1)Some protected dormant buds of mat-form plants can survive dry conditions for long periods, up to 2 years in one case. (2)Plants will withstand periods of stress, both low temperature and dewatering, as dormant buds.

(1)http://pi.cdfa.ca.gov/weedInfo/SALVINIA2.html (2)http://agriculture.state.az.us/PSD/giant_sal1.htm

8.03

1)The most straightforward control is by preventing additional infestations. Salvinia reproduces so rapidly that infestations rapidly become impossible to eradicate using manual methods! A biocontrol has been developed (Cyrtobagous salviniae) and may be effective in the near future. Until then chemical control may be the only viable option available.
(2)Chemical: Several chemicals are effective, and are described in Parsons and Cuthbertson (1992).

(1)http://tncweeds.ucdavis.edu/alert/alrtsalv.html (2)http://www.hear.org/pier/samol.htm

8.04

(1)Easily regenerates from fragments, benefiting from cultivation (2)Salvinia molesta will withstand periods of stress, both low temperature and dewatering, through latent buds.

(1) http://www.ceris.purdue.edu/fedweb/0107/24/0001.html (2)http://salvinia.er.usgs.gov/html/identification.html

8.05

[plant has become a serious pest in Hawaii] (1)The salvinia weevil, Cyrtobagous salviniae, is a proven biocontrol agent for Salvinia molesta (Thomas and Room 1986b; Cilliers 1991). This tiny insect causes immense damage to plants by tunneling through rhizomes and feeding on terminal buds. Such feeding acts to greatly reduce large infestations of S. molesta and to maintain low plant population levels (Sands et al. 1983; Sands and Schotz 1985; Room et al. 1981).
The salvinia weevil ranges naturally in southeastern Brazil, Bolivia, Paraguay and northern Argentina (Wibmer and O'Brien 1986; Calder and Sands 1985). The weevils experimentally released October 2001 by USDA/ARS in Texas and Louisiana were imported under permit from Australia, where they are reared and used for biological control of Salvinia molesta.
(2)Biological: "Biological control is the most effective method of removing salvinia. Spectacular results have been obtained in parts of Australia and it seems likely that they will be repeated elsewher

(1)http://salvinia.er.usgs.gov/html/salvinia_weevil.html (2)http://www.hear.org/pier/samol.htm


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