Invasiveness Assessment - St. Barnaby’s thistle (Centaurea solstitialis) 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 St Barnaby's thistle.

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: St. Barnaby’s thistle
Scientific name: Centaurea solstitialis

Question	Comments	Reference	Rating
Establishment
Germination requirements?	Seeds germinate in autumn.	P&C (1992)	MH
Establishment requirements?	Can establish under moderate canopy - occurs orchards, vineyards, oak woodlands.	Woo et al (1999) Maddox et al (1985)	MH
How much disturbance is required?	Invades crops & pastures.	P&C (1992) Maddox et al (1985)	MH
Growth/Competitive
Life form?	Annual/biennial erect herbs - ‘Other’.	P&C (1992)	L
Allelopathic properties?	Allelopathic compounds restrict growth of other species & also decrease germination of its own seeds.	P&C (1992)	MH
Tolerates herb pressure?	Not readily eaten by stock except when it is very young, due to the presence of spines.	P&C (1992)	MH
Normal growth rate?	Competes with pastures and crops. Yellow star thistle germinates & grows more rapidly than many of its competitors under a variety of conditions (Larson et al 1997).	P&C (1992)	H
Stress tolerance to frost, drought, w/logg, sal. etc?	Tolerant of drought (occurs in semi-arid rangeland), fire (although not continued burns), some salinity and frost.	Woo et al (1999) DiTomaso et al (1999) Larson et al (1997)	MH
Reproduction
Reproductive system	Reproducing by seed → not sure if cross &/or self pollination	P&C (1992)	ML
Number of propagules produced?	More than 10,000 seeds have been recorded on some plants but the average is much less	P&C (1992)	H
Propagule longevity?	Most seeds germinate the following year, but some seeds can last 10 years or more in the soil.	Calihan et al (1993) Woo et al (1999)	ML
Reproductive period?	Forms monocultures (dense infestations) →see pic P&C (1992) p.203. Densities of 5-7 m plants/ha have been recorded.	P&C (1992) Callihan et al (1993)	H
Time to reproductive maturity?	Annual	P&C (1992)	H
Dispersal
Number of mechanisms?	Seeds – wind, water, contaminant of agricultural produce including commercial seed, vehicles, machinery, wool & fodder. Also by birds (Woo et al 1992). However, is not the primary dispersal mechanism. Seeds not ingested by birds, but rather attach to bird feathers (Callihan et al 1993). In addition, dispersal by birds not noted in Australia by P&C (1992). CONTRADICTS During seed dispersal, birds feed heavily on yellow star thistle achenes… Birds have been implicated in both long & short distance dispersal of weed seeds. (See Roche 1992 p.64)	P&C (1992)	MH
How far do they disperse?	Plumed seeds can disperse 1.5 m by wind and many seeds disperse over longer distance in fur, feathers or human activity.	Woo et al (1999)	ML

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