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Invasiveness Assessment - Caltrop (Tribulus terrestris) 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 Caltrop.

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 - 1026 KB)
To view the information PDF requires the use of a PDF reader. This can be installed for free from the Adobe website (external link).

Common Name: Caltrop
Scientific name: Tribulus terrestris

Question
Comments
Reference
Rating
Establishment
Germination requirements?“Seeds germinate after late spring and summer rains’.
P & C (1992 p. 640)
MH
Establishment requirements?Occurs in open areas (i.e. crops and pasture).
P & C (1992 p. 640/41)
ML
How much disturbance is required?Invades pastures and crops (e.g. vineyards, irrigated cotton).

“Only in recent years has it invaded horticultural and agricultural crops and pastures”.
P & C (1992 p. 641)
P & C (1992 p. 641)
MH
Growth/Competitive
Life form?Annual herb.

Other.
P & C (1992 p. 640)
L
Allelopathic properties?“There is evidence that Caltrop has an Allelopathic effect on some plants” (e.g. grass seedlings).
P & C (1992 p. 642)
ML
Tolerates herb pressure?“They do not normally graze Caltrop when other feed is available but, in some cases there is no alternative”.
P & C (1992 p. 642)
MH
Normal growth rate?Competes with pastures and a variety of crops throughout Australia. (e.g. cereals, cotton, vines and peanuts).
P & C (1992 p. 641)
MH
Stress tolerance to frost, drought, w/logg, sal. etc?Its extensive root system allows it to survive droughts.

Its extensive distribution in Australia would allow it to tolerate some frost and likely other conditions.
P & C (1992 p. 642)
(Map p. 640)
ML
Reproduction
Reproductive system“Reproducing by seed”.
P & C (1992 p. 640)
L
Number of propagules produced?“Fruit are thus formed continually throughout the summer and autumn and according to Indian studies up to 1,000 fruit can be produced on each plant”.
P & C (1992 p. 641)
H
Propagule longevity?‘Buried seed remains viable for several years”.
P & C (1992 p. 641)
ML
Reproductive period?Annual herb.
P & C (1992 p. 640)
L
Time to reproductive maturity?“The first flowers may be formed when plants are only three weeks old and the first fruit at five or six weeks”.
P & C (1992 p. 641)
H
Dispersal
Number of mechanisms?Animals, vehicle tyres, shoes and almost any object which is placed on it.
P & C (1992 p. 641)
MH
How far do they disperse?Animals, vehicles could easily disperse seeds numerous km.
H



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