Invasiveness Assessment - Ragwort (Senecio jacobaea) in Victoria (Nox)

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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 Ragwort.

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: Ragwort
Scientific name: Senecio jacobaea

Question	Comments	Reference	Rating
Establishment
Germination requirements?	“Seeds have no inherent dormancy and germinate at any time of the year, but mostly in autumn shortly after seed fall”.	P & C (1992 p. 299)	H
Establishment requirements?	“While scattered populations occur in shade it is mostly found in open, sunny locations”.	Muyt (2001)	MH
How much disturbance is required?	Invades undisturbed vegetation e.g. heathland and heathy woodland. “Invasive on the margins of sub alpine lakes in Central Tasmania”.	Carr et al (1992) Muyt (2001 p. 113)	H
Growth/Competitive
Life form?	Erect biennial or perennial (rarely annual) herb. Other.	P & C (1992 p. 299)	L
Allelopathic properties?	No Allelopathic properties described.		L
Tolerates herb pressure?	“Cutting, grazing or ineffective chemical control stimulates regeneration from the crow, thereby converting biennial plants to perennials”.	P & C (1992 p. 300)	MH
Normal growth rate?	“When firmly established, ragwort dominates an area almost to the exclusion of all other plants…maintaining a vigorous pasture helps reduce, but not prevent, ragwort invasion”.	P & C (1992 p. 301)	MH
Stress tolerance to frost, drought, w/logg, sal. etc?	Tolerant of frost (occurs in sub alpine areas of Tasmania). Assumed tolerant of some drought (occurs in central Victoria, WA and California).	Muyt (2001 p. 113) P & C (1992) Bassard et al (2000)	ML
Reproduction
Reproductive system	“Reproducing from crowns, roots and by seed”.	P & C (1992 p. 299)	H
Number of propagules produced?	“It has been estimated that a well developed multi-stemmed ragwort plant produces about 250,000 seeds per year of which about 80% may be viable”.	P & C (1992 p. 301)	H
Propagule longevity?	“Can remain viable for at least 8 years and germinates when brought to the surface”.	P & C (1992 p. 301)	ML
Reproductive period?	Biennial or perennial (if aerial growth stimulated by cutting, grazing etc).	P & C (1992 p. 300)	ML
Time to reproductive maturity?	“Only very rarely do plants flower in their first summer…some plants flower in the second summer but many more may be as much as 5 years old before developing flowering stems”. (P & C 1992 p. 299).		MH
Dispersal
Number of mechanisms?	Water, animals, vehicles, clothing, hay and chaff, wind.	P & C (1992 p. 300)	MH
How far do they disperse?	See ‘dispersal’ in P & C (1992 page 300 & 301). Very descriptive.		H

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