Invasiveness Assessment - Cobblers pegs (Bidens pilosa) in Victoria
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Plant invasiveness is determined by evaluating a plant’s biological and ecological characteristics against criteria that encompass establishment requirements, growth rate and competitive ability, methods of reproduction, and dispersal mechanisms.
| Each characteristic, or criterion, is assessed against a list of intensity ratings. Depending upon information found, a rating of Low, Medium Low, Medium High or High is assigned to that criterion. Where no data is available to answer a criterion, a rating of medium (M) is applied. A description of the invasiveness criteria and intensity ratings used in this process can be viewed here. |
The following table provides information on the invasiveness of Cobbler's pegs.
A more detailed description of the methodology of the Victorian Weed Risk Assessment (WRA) method can be viewed below:
Victorian Weed Risk Assessment (WRA) method (PDF - 630 KB)
Victorian Weed Risk Assessment (WRA) method (DOC - 1 MB)
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Common Name: Cobbler's Pegs
Scientific name: Bidens pilosa
| Question | Comments | Rating | Confidence |
| Establishment | |||
| Germination requirements? | Optimum temperature for germination is between 20 and 35oC. Day-time temperatures below 15oC and above 45oC are unfavourable for germination (Reddy & Singh 1992). Requires natural seasonal disturbances for germination, e.g. Spring/Summer temperatures | MH | H |
| Establishment requirements? | In one study, shading by the leaf canopy was shown to be effective in inhibiting germination of B. pilosa, (Fenner 1980) and in another study, no seedlings survived in a shade environment typical of that found in a rainforest understorey (Pattison, Golstein & Ares 1998). Can grow in partial shade (ESC 2002) but unable to establish under a moderate canopy. Requires access to light to establish (Holm et al 1977). | ML | M |
| How much disturbance is required? | Documented as invading grassland, heathland and forest (Weber 2003) as well as ‘remnant grassy vegetation’ in NSW (ESC 2002). Disturbance need only be minimal for B. pilosa to invade (SSC 2003). Establishes in only minor disturbed natural ecosystems, e.g. grasslands. | MH | MH |
| Growth/Competitive | |||
| Life form? | Erect annual or short-lived perennial shrubby herb to 150 cm in height (Smith 1985; Holm et al 1977). Lifeform: Other | L | MH |
| Allelopathic properties? | Several studies have shown Bidens pilosa to have strong allelopathic influences. Leaf or root extracts significantly suppressed germination and seedling growth of a number of crops, including, soya beans, mung beans, rice, maize, radish, cucumber, lettuce, sorghum and ground nuts (Bhatt, Tomar & Misra 2001; Zeng & Luo 1995; Stevens & Tang 1985; Singh & Hazarika 1996). It has also been suggested that the allelopathic compounds remain active in the dried parts of the weed and are released during decomposition (Singh & Hazarika 1996). Allelopathic properties seriously affect some plants. | MH | H |
| Tolerates herb pressure? | In one study, regular manual ‘topping’ of B. pilosa plants increased the shoot and leaf yield of plants, with more regular 2 weekly harvesting producing greater yields. Plants harvested 9 times, at 3 weekly intervals, demonstrated development of flower buds (Norman 1994). Plants are likely to exhibit a similar response to herbivory. Species recovers quickly, and capable of flowering under moderate herbivory pressure. | MH | MH |
| Normal growth rate? | This species will out-compete native species on exposed margins and in revegetation sites (SSC 2003). Found to grow three times faster than a species of similar life-form, Bidens sandwicensis (Pattison, Golstein & Ares 1998). Moderately rapid growth that is likely to equal competitive species of the same life form or exceed some other species of the same life form. | MH | MH |
| Stress tolerance to frost, drought, w/logg, sal. etc? | Tolerates arid conditions (GCW 2001), dry infertile soils and is often most prolific on warm north facing rocky slopes (ESC 2002). It will survive all but the most extreme droughts (Labrada 2001). Above ground parts are killed by heavy frosts but plants will grow back quickly from roots. It can withstand temperatures down to –15oC (Labrada 2001) and known to grow at an altitude of 3,600 m in Peru (Becker et al 1998). Occurs in wetlands (Calflora 2007) and wet dune slacks (Moreno-Casasola P & Vazquez G 1999). It is not fire tolerant but quickly invades burnt areas (Smith 1985). Evidence suggests it is moderately tolerant of drought, water logging and frost but is susceptible to fire. The level of tolerance is not clear from the information available so a medium rating has been assigned. | M | M |
| Reproduction | |||
| Reproductive system | Sexual (self and cross pollination) (Grombone-Guaratini, Solferini & Semir 2004). | ML | H |
| Number of propagules produced? | A single plant may produce 3,000-6,000 seeds per year (Weber 2003). Produces above 2,000 propagules. | H | MH |
| Propagule longevity? | Seeds were found to survive for 3-4 years in the soil seedbank (Voll et al 2001). Seeds survive less than 5 years. | L | H |
| Reproductive period? | Forms dense stands that cover large areas eliminating native vegetation (Weber 2003). Evidence suggests that species forms self-sustaining monocultures. | H | MH |
| Time to reproductive maturity? | In Argentina, the majority of a population was found to start flowering 4 months after germination (Gurvich et al 2004). Reaches maturity and produces viable propagules in under a year. | H | H |
| Dispersal | |||
| Number of mechanisms? | Seeds are widely dispersed by adhering easily to clothes and animal fur (Weber 2003) and are also spread by wind, water and soil (SSC 2003; ESC 2002). | MH | MH |
| How far do they disperse? | ‘The aggravating little needles will embed themselves in your clothing by the dozens every time you brush past the stems’ (Floridata 2007)’. Seeds are widely dispersed by adhering easily to clothes and animal fur (Weber 2003). Due to the ease of seed attachment to clothing and fur, it is very likely that at least one propagule will disperse greater than one kilometre. | H | M |
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