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)
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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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