Invasiveness Assessment - Scotch thistle (Onopordum acanthium) 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 Scotch 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: Scotch thistle
Scientific name: Onopordum acanthium

Question	Comments	Reference	Rating
Establishment
Germination requirements?	“Seeds germinate at any time of year”.	P & C (1992 p. 217)	H
Establishment requirements?	Occur in open areas e.g. pastures.		ML
How much disturbance is required?	“Favours clover and Lucerne pastures and fertile river flats more than areas of unimproved native vegetation”.	P & C (1992 p. 217)	MH
Growth/Competitive
Life form?	Annual or biennial herb. Other.	P & C (1992 p. 216)	L
Allelopathic properties?	No Allelopathic properties described.		L
Tolerates herb pressure?	“The weed is rejected by stock because of the above spines”.	P & C (1992 p. 218)	MH
Normal growth rate?	“It is a competitive weed of Australian pastures”. “In New South Wales, Scotch Thistle occurs with the closely related Illyrian thistle and some infestations in the State are a mixture of the two species plus various intermediate taxa”. (P & C 1992 p. 218).	P & C (1992 p. 216)	MH
Stress tolerance to frost, drought, w/logg, sal. etc?	Assumed tolerant of frost (occurs in S. Tas.) and drought (occurs in C. Vic. & NSW).	P & C (1992 p. 216)	ML
Reproduction
Reproductive system	“Reproducing by need”. “There can be some local spread of severed root pieces”.	P & C (1992 p. 216) P & C (1992 p. 217)	H
Number of propagules produced?	“A prolific seeder and a single plant may produce over 20,000 seeds”.	P & C (1992 p. 218)	H
Propagule longevity?	“Buries seed is long lived and germinates when brought near the surface hence, plants may appear on recently cultivates areas where there has been no seeding for several years”.	P & C (1992 p. 218)	MH?
Reproductive period?	Annual or biennial herb.	P & C (1992 p. 216)	L
Time to reproductive maturity?	Annual or biennial herb.	P & C (1992 p. 216)	H
Dispersal
Number of mechanisms?	Equipment, wool, clothing, wind, animals (internal) and possibly birds.	P & C (1992 p. 217)	MH
How far do they disperse?	“Seeds remain viable after passing through the digestive tracks of sheep”.	P & C (1992 p. 217)	MH

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