Invasiveness Assessment - Fleabane (Conyza sumatrensis) 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 Fleabane / tall fleabane

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: Fleabane / Tall fleabane
Scientific name: Conyza sumatrensis (formerly/synonyms C. albida and C. floribunda)

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	C.albida (syn C.sumatrensis) was found to require temperatures between 10^o and 25^oC and light to germinate (Zinzolker et al, 1985) in a laboratory environment. Most seeds emerge in autumn but some seeds can also germinate in Spring (Thebaud et al, 1996). However Spring seedlings have a reduced survivorship compared to autumn germinants. Seed germinates within 1-4 weeks in acid, sandy soils (Case and Crawley, 2000). The species requires certain conditions such as temperature and moisture to be adequate in order to germinate.	MH	H
Establishment requirements?	The likelihood of C.sumatrensis recruitment was positively correlated with the extent of bare ground and increased disturbance (Case and Crawley, 2000). The plant has been noted as being a poor competitor against native species (Case and Crawley, 2000). The plant most commonly established in areas of disturbed open ground with access to light and minimal interspecific competition. The plant appears to require more specific requirements to establish such as open space and direct light.	ML	H
How much disturbance is required?	C.sumatrensis is a plant widely naturalised in disturbed soils (Calflora) open cultivated fields and pasture and wasteland (Everett, 2002; Walsh and Entwisle, 1996). It has been found in roadsides, disturbed wetlands and wasteland from Perth to Albany (Hussey et al, 1997) with the occasional plant often found in undisturbed bush (ESC, 2004). In France C.sumatrensis occurs in gardens, vineyards and in old fields (Case and Crawley, 2000). In the Mediterranean C. sumatrensis typically establishes and persists in old fields whose age ranges from 0-30 yr abandonment (Thebaud et al, 1996). In Greece it grows mainly in urban habitats (Economou et al, 2002) but also occurs in natural and agricultural ecosystems (Economou and Nekarios, 2003). Has been found to establish in disturbed areas of native vegetation and in natural sand dunes and grasses (Thebaud and Abbott, 1995). In Australia it is able to establish in dry coastal heath, heathland, mallee shrubland, grasslands, sclerophyll forests, woodland, riparian vegetation and freshwater wetland (Carr et al, 1992). It is a successful coloniser that can take advantage of disturbances (Case and Crawley, 2000) and can tolerate a variety of habitats and environmental conditions (Economou et al, 2002). The species requires low interspecific competition, long distance dispersal and regular disturbance for successful establishment and colonisation (Case and Crawley, 2000). The species prefers highly disturbed areas and has the capacity to establish in native ecosystems also.	ML	H
Growth/Competitive
Life form?	Winter annual-biennial herb to 2 m high (Walsh and Entwisle, 1996).	L	MH
Allelopathic properties?	The stems, leaves and inflorescence of C.albida (syn C.sumatrensis) have been recorded as having an allelopathic influence on oat growth. Oat (Avena sativa) growth was inhibited from phytotoxic activity of upper leaves and inflorescence tissues of C.albida (syn C.sumatrensis) (Economou et al, 2002).	MH	H
Tolerates herb pressure?	Case and Crawley (2000) found that rabbit grazing had strong negative effects on C. sumatrensis recruitment and survival. Unprotected plants seldom developed beyond rosette phase under such grazing conditions (Case and Crawley, 2000). The authors noted that the species cannot survive high intensity rabbit grazing. Weed is palatable to livestock and native browsers such as wallabies (ESC, 2004). In addition Thebaud et al (1996) found that herbivory weakly but significantly reduced survival to flowering. The plant tolerates grazing however potential fitness may be sensitive under extreme grazing pressure. Sensitive to extreme grazing but withstands moderate grazing pressure. Reproduction strongly inhibited by herbivory but weed may still persist.	MH	H
Normal growth rate?	Denser more competitive than other Conyza spp (C. canadensis) (Thebaud et al, 1996). The plant exhibits vigorous rapid growth (Economou and Nektarios, 2003) that exceeds species of the same life form.	H	H
Stress tolerance to frost, drought, w/logg, sal. etc?	Seedlings from the spring cohort generally experience very high post emergence mortality through desiccation in the Mediterranean region (Thebaud et al, 1996) indicating an intolerance to drought conditions. Early seedling mortality was recorded by Thebaud et al (1996) due to abiotic stresses such as autumn frosts or spring drought. Rosettes are able to flower under moderate shade (Ohtsuka, 1998) however germination requires sufficient light. The plant is killed by fire and has been described a establishing in disturbed wetlands (Hussey et al, 1997) indicating a degree of tolerance to waterlogging. Therefore the plant is defiantly susceptible to three environmental stresses, drought, fire and frost, but little information exists on its tolerance to salinity.	L	H
Reproduction
Reproductive system	The species reproduces by seed (Case and Crawley, 2000). Species are self fertile (Thebaud et al, 1996). No information was found on reproduction of this species.	ML	MH
Number of propagules produced?	A related species C. bonariensis (Pruski, 2006) plant produces on average of 110,000 seeds (Wu and Walker, 2004). One single flower head contains 190 to 550 seeds with an average of 400 per flower head (Wu and Walker, 2004). C. sumatrensis has been noted as having a prolific seed set; it produces and average of 94.6 florets per head (capitulum) (Thebaud and Abbott, 1995). Based on the above numbers and sited images of inflorescence (RBGSYD, Walsh and Entwisle, 1996) show numerous flower heads indicating that the plant produces over 2000 seeds per flowering event.	H	MH
Propagule longevity?	Seeds do not remain dormant and under laboratory conditions, seed longevity is only 2-3 years (Thebaud et al, 1996). Seeds germinate whenever conditions are ideal (Case and Crawley, 2000). In the closely related species C. bonariensis (Thebaud and Abbott, 1995) seeds were 6% viable after being buried for three years (Wu et al, 2007)	L	H
Reproductive period?	The species is a winter annual-biennial herb to 2 m high (Walsh and Entwisle, 1996) and the flowering period lasts 1-4 months (Thebaud et al, 1996). Therefore the mature plant produces viable propagules for only 1 year.	L	MH
Time to reproductive maturity?	The species is a winter annual-biennial herb to 2 m high (Walsh and Entwisle, 1996). Thebaud and Abbott (1995) recorded the average time to bolting in C. sumatrensis as 11 weeks. Subsequently the average age at flowering in the same species was recorded as 19.8 weeks (Thebaud and Abbott, 1995). In addition Cleland and Suding found that the mean day of peak flowering in C. floribunda (Syn C. sumatrensis) occurred at 120 days after germination. Therefore the plant will produce propagules in under a year.	MH	MH
Dispersal
Number of mechanisms?	C.sumatrensis seeds are very light and all bear a pappus that facilitates wind transport (Thebaud et al, 1996, Carr et al, 1992). Seeds are also dispersed by water (Carr et al, 1992) and human dispersed through vehicles and mechanical means (ESC, 2004). There is a possibility that seeds are transported by animals externally (Carr et al, 1992). The propagules are very light and mostly spread by wind but are also spread by humans, animals, water or vehicles.	H	H
How far do they disperse?	High dispersal potential (Economou and Nektarios, 2003). Very likely that at least one propagule will disperse greater than one kilometre.	H	MH

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