RMD-13-04: Consolidated Pest Risk Management Document for pest plants regulated by Canada
Appendix 12A: Pest Risk Assessment Summary for Senecio inaequidens (South African ragwort)

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Identity of Organism

Name: Senecio inaequidens (Asteraceae) (USDA-ARS 2009)

Synonyms: Senecio burchellii (CAB International 2007)

English common names: South African ragwort, narrow-leaved ragwort (CAB International 2007), fireweed, variable groundsel (Mondragón Pichardo and Vibrans 2005)

French common names: Séneçon du Cap (CAB International 2007)

Taxonomic note: There has been considerable taxonomic confusion regarding Senecio inaequidens, which is owed to morphological variation within the species and superficial similarity between two groups of species (Senecio madagascariensis complex and Senecio lautus complex) (CAB International 2007). Traditionally, a distinction has been made between Senecio inaequidens and Senecio madagascariensis, although recent research suggests that they are conspecific and differ in ploidy level only (CAB International 2007; Lafuma et al. 2003). It was found that a tetraploid form was introduced in Europe, and a diploid form in Australia, Argentina, Mexico and possibly the U.S. (Hawaii), although both forms originated in South Africa (Lafuma et al. 2003). The tetraploid form is referred to as Senecio inaequidens, and the diploid form may actually be what has been referred to as Senecio madagascariensis.

Overall, the distinction between Senecio inaequidens and Senecio madagascariensis is still 'controversial' (CAB International 2007). For the purposes of risk assessment, they are considered to be distinct taxa in accordance with the USDA Germplasm Resources Information Network (GRIN) (USDA-ARS 2009), although some of the references consulted treated the two together. It should be noted that this distinction between taxa may disappear in the future, which would require an update to the taxonomy presented in this risk assessment. At this time, since Senecio madagascariensis possesses many of the same invasive qualities as Senecio inaequidens (Lafuma et al. 2003), the plant health risk posed by the two taxa should probably be considered concurrently. Senecio inaequidens and Senecio madagascariensis are both listed on the U.S. Federal Noxious Weed List (USDA-APHIS 2006).

Description: Senecio inaequidens is a broadleaved, herbaceous short-lived perennial shrub that reaches 100 cm in height (CAB International 2007). It has erect stems that often branch from the base, bright green alternate leaves that usually clasp the stem, and yellow flowers composed of 7 to 13 female ray florets and numerous perfect disc florets (CAB International 2007). The seeds are achenes, 2 to 2.5 mm long, with a white pappus, 2 to 3 times as long (EPPO 2006a). The specific epithet inaequidens means unequal teeth, likely referring to variation in the degree of dissection and the width of the lobes of the leaves (CAB International 2007).

Organism Status

It is not reported to occur in Canada (CAB International 2007; CFIA 2008; Scoggan 1979), with the exception of Heger and Böhmer (2006), who refer to Garcia-Serrano et al. (2004). However, there is no statement in the latter reference (Garcia-Serrano et al. 2004) indicating that Senecio inaequidens is present in Canada, so the reference appears to have been used in error (possibly because it was published in the Canadian Journal of Botany). No evidence of its cultivation in Canada was found either (CNLA 2008; Isaacson and Allen 2007). Based on this information, for the PRA area, Senecio inaequidens is considered absent.

Current Regulatory Status

It is not currently regulated in Canada. It is regulated as a federal noxious weed in the US but not regulated in any of the states.Summary of pathways for Senecio inaequidens (South African ragwort). It is not currently regulated by any European country (EPPO 2006), but is on the EPPO List of Invasive Alien Plants and is considered to impose an important threat to plant health, the environment and biodiversity in the EPPO region. Senecio madagascariensis, a very closely related taxon, is listed as a noxious weed in Hawaii (HEAR 2003), Australia (i.e., New South Wales, Western Australia, Queensland and the Australian Capital Territory (Australian Weeds Committee 2008; EPPO 2006)) and in Mexico.

Probability of Entry

Although natural dispersal is an important pathway of introduction in its current range, natural dispersal is unlikely to be means of introduction for into Canada (Table 1). However, there are a number of potential unintentional pathways for introduction of Senecio inaequidens into Canada including wool imports, contaminated hay or grain, and as a generalist contaminant on travelers or on surfaces.

Table 1: Summary of pathways for Senecio inaequidens (South African ragwort)
Type of pathway Specific Pathways
Natural dispersal
  • wind is a pathway for dispersal and can carry the seeds long distances
  • water is considered a possible means of dispersal
The risk of natural dispersal into Canada is low because there are no populations near Canadian borders.
Intentional IntroductionNone identified
Unintentional Introduction
  • as a seed contaminant on wool imports
  • as a seed contaminant in hay, grain, ornamental plants, soil, or on the surface of containers
  • seed contaiminant on clothes and shoes, livestock, building materials, or on tires

These unintentional pathways are low risk.

Probability of Establishment

It native to southern Africa (Lesotho, South Africa, Swaziland, Mozambique, Botswana, and Namibia) and is naturalized elsewhere (CAB International 2007) (Figure 1 ). Its reported range is variable among sources due to the taxonomic confusion mentioned above. It is currently found in many European countries, from Spain to Poland, and including the northern countries of Norway and Sweden (CAB International 2007; Heger and Böhmer 2006). Although it has been reported in Finland, it does not appear to have established there (Heger and Böhmer 2006). It was also recently discovered in Taiwan (Jung et al. 2005). Reports of Senecio inaequidens from Mexico, Argentina (Figure 1), and possibly Colombia, may refer to S. madagascariensis (Lafuma et al. 2003).

Figure 1: Distribution map of Senecio inaequidens (South African ragwort)

Figure 1. Description follows.
Description of Figure 1:

This image shows the distribution map of Senecio inaequidens (South African ragwort). You can see a map of the world under which there is a legend that is subdivided into two sections: national records and subnational records. Under national records there is a yellow square with a filled in red circle inside it symbolizing that records are present. Secondly, there is a yellow square inside which there is a red outline of a circle signifying that it is present only in some areas. Subnational record also has two symbols: a yellow square with a green filled in circle denoting present records on the subnational level and a yellow square with an outline of a green circle inside it signifying that they are only present in some areas. Southern Africa is covered in yellow containing filled in red circles in regions such as: Lesotho, South Africa, Swaziland, Mozambique, Botswana, and Namibia. Moreover, a great many European countries ranging from Spain to Poland extending to Norway and Sweden are covered in yellow while most contain complete red circles, Ireland and the United Kingdom have green full circles. Argentina and Mexico also contain complete red circles.

Source: EPPO 2008

In southern Africa, Senecio inaequidens grows in grasslands at high elevations (1400-2800 m), along the margins of periodically flooded streams, and in ruderal habitats (CAB International 2007). In Europe, this species establishes in a wide variety of habitats and on a wide range of soils, although it prefers warm, dry disturbed sites with well-drained soils (CAB International 2007). Habitats include railway lines, roadsides, the dividing strips of highways, river ports, flat roofs, flower tubs, logging areas, storm-damaged forests, burnt land industrial sites, disused quarries, rocky sites, coastal dunes, crops and pastures from sea level to approximately 600 m (EPPO 2006; Heger and Böhmer 2006).

There is potential for Senecio inaequidens to establish in Canada due to its opportunistic nature and its ability to establish in temperate climates. An EPPO datasheet on Senecio inaequidens describes it as hardy and well adapted to zone 7 (EPPO 2006) (likely referring to USDA Plant Hardiness Zone 7). Based on the results of the NAPPFAST System, it appears capable of establishing in zone 6 as well, based on records from Norway, Sweden (GBIF 2008) and Switzerland (Heger and Böhmer 2006). In Canada, zone 6 and above includes coastal British Columbia and Vancouver Island, a small area in extreme southern Ontario, and some of the coastal areas of Nova Scotia and Newfoundland (Figure 2).

Figure 2: Potential distribution of Senecio inaequidens (South African ragwort) in Canada

Note: As predicted by the NAPPFAST system. The red shading corresponds to areas at risk which represent global plant hardiness zones 6 and above.

Figure 2. Description follows.
Description of Figure 2:

This image shows the potential range of Senecio inaequidens (South African ragwort) in Canada and northern America through the use of a map. Red is used to indicate the regions in which Senecio inaequidens could survive in according to the Canadian Plant Hardiness Zones map, in this case NAPPFAST Hardiness Zones 6. In Canada, the potential range of Senecio inaequidens includes coastal British Columbia and Vancouver Island, a small area in extreme southern Ontario, and some of the coastal areas of Nova Scotia and Newfoundland. Most of the red can be found in the U.S., this includes the greater parts of the east and west coasts as well as areas located near the Great Lakes extending downwards beyond the image.

Probability of Spread

It is a prolific seed producer that is dispersed naturally by wind and unintentionally by humans in association with clothes, shoes, soil movement, road and rail vehicles, building materials, hay, grain, ornamental plants, livestock, and wool (CAB International 2007; EPPO 2006; Heger and Böhmer 2006). In Europe, its initial introduction occurred in association with sheep wool imports and then it spread rapidly along linear anthropogenic structures, especially railway tracks and highways (Heger and Böhmer 2006). It grows vigorously and is readily adaptable to a wide range of environments (EPPO 2006).

Potential Economic Consequences

From various foci of introduction in Europe, Senecio inaequidens began to spread and by the 1970s was considered invasive in many European countries (EPPO 2006). It continues to expand its range today, and tends to form very high infestation levels (EPPO 2006). Senecio inaequidens is known to colonize vineyards and to reduce the value of pastures (EPPO 2006). The plants contain pyrrolizidine alkaloids, which are toxic to livestock and humans (EPPO 2006) and may affect consumer demand for milk and honey (EPPO 2006).

Control or eradication in Europe is considered very difficult and costly (EPPO 2006). Negative economic consequences associated with herbicide resistance of Senecio inaequidens have been reported from German railways (100,000 Euros per year) (Heger and Böhmer 2006; Reinhardt et al. 2003). The EPPO Pest Risk Analysis for this species indicates that economic risks for this species are medium to high (EPPO 2006). [Note that there is a discrepancy between this source and CAB International (2007), which considers economic impacts to be minimal.] The introduction of Senecio inaequidens in the PRA areacould also threaten Canada's ability to export commodities to the United States (where it is a designated federal noxious weed) and potentially elsewhere. The achenes are similar in size to those of Senecio vulgaris L. (common groundsel), a known contaminant of forages and grasses in Canada.

Potential Environmental and Social Consequences

It is known to invade natural habitats (e.g., dunes, cliffs, temporary ponds) and may threaten biodiversity (EPPO 2006). It is considered capable of modifying landscapes and is also an "colonizer of wasteland" (EPPO 2006). The EPPO Pest Risk Analysis for this species indicates that environmental risks for this species are medium to high and social risks are low to medium (EPPO 2006). Note again that there is a discrepancy between this source and CAB International (2007), which considers environmental impacts to be minimal.

Uncertainty

It may only be marginally hardy to NAPPFAST zone 6. It is certainly widespread in zone 7 in Europe, but if it could only survive to zone 7, its potential range in Canada would be limited to coastal and southwestern BC.

Although Senecio inaequidens is considered to have negative impacts on crops and pastures, information on the severity of these impacts, or on what crop species it invades (other than vineyards) is scarce.

Conclusion

The pest risk assessment concluded that Senecio inaequidens would likely become weedy or invasive in parts of Canada, including southern and coastal British Columbia, extreme southern Ontario and parts of the Maritimes, if introduced.

Technical Issues for Consideration

Senecio taxa may be distinguished based on shorter achenes (1.5 mm to 2.0 mm) and hairs confined to the achene grooves in Senecio madagascariensis as compared to longer achenes (2.5 mm) and completely hairy achenes in Senecio inaequidens. These differences should be treated with caution as they are based on limited sampling (CAB International 2007; Radford et al. 2000).

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