Invasiveness Assessment - Parthenium weed (Parthenium hysterophorus) 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 Parthenium weed.

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: Parthenium weed
Scientific name: Parthenium hysterophorus

Question	Comments	Reference	Rating
Establishment
Germination requirements?	“Seeds germinate at any time of year provided moisture is available.” Opportunistic germinator.	Parsons & Cuthbertson (2001)	H
Establishment requirements?	“Seeds exposed to light showed higher germination than those in darkness but with time this difference tended to become smaller.” Can establish without additional factors.	Tamado et al (2002)	H
How much disturbance is required?	“It occurs as a weed in disturbed areas on roadsides, railway reserves, stock yards, cultivated fields, run-down pastures and vacant lots.” “Parthenium does not compete with established perennial grasses as it requires bare soil to germinate.” Requires some disturbance or bare soil to establish.	Parsons & Cuthbertson (2001) McFadyen (1992)	ML
Growth/Competitive
Life form?	Short-lived annual. Other.	McFadyen (1992)	L
Allelopathic properties?	“The allelopathic nature of P. hysterophorus has been well documented.” It is known to inhibit the germination of a large number of trees, shrubs and crops. Examples of such species are Casuarina, Acacia, Eucalyptus, rice, wheat, barley mung beans and sorghum. Major allelopathic properties inhibiting the growth of many plants.	Evans (1997)	H
Tolerates herb pressure?	“Livestock do not normally eat the weed but hungry animals, particularly sheep, may do so if nothing else is available.” “Under continued grazing pressure, parthenium weed will completely dominate the pasture, forming pure stands over areas up to 5,000 hectares.” Even under grazing, the plant can still dominate leading to monoculture.	Parsons & Cuthbertson (2001) McFadyen (1992)	H
Normal growth rate?	“…plants commence flowering within 4 to 8 weeks of germination, 4 weeks being more likely in dry periods.” Rapid growth to flowering stage likely to exceed the growth rate of similar species.	Parsons & Cuthbertson (2001)	H
Stress tolerance to frost, drought, w/logg, sal. etc?	“Flowering… continues until drought or frost kills the plant.” Not tolerant to either drought or frost.	McFadyen (1992)	L
Reproduction
Reproductive system	Annual herb, reproducing by seed. “Self-compatibility of parthenium weed has not been observed in plants grown in isolation in Australia.” Cross-pollination only.	Navie et al (1998)	L
Number of propagules produced?	“Parthenium weed seeds prolifically, each plant producing about 15,000 seeds.” Above 2,000 seeds produced annually.	Parsons & Cuthbertson (2001)	H
Propagule longevity?	“Some field evidence exists that parthenium weed achenes can remain viable after being buried for at least 4–6 years.” Many seeds survive for a period of less than 10 years.	Navie et al (1998)	ML
Reproductive period?	Short-lived annual. Produces propagules for one growing season (i.e. annually).	McFadyen (1992)	L
Time to reproductive maturity?	Plant commences flowering within 4 to 8 weeks of germination. Reaches maturity in less than one year.	Parsons & Cuthbertson (2001)	H
Dispersal
Number of mechanisms?	“Dispersal of parthenium weed achenes occurs locally by wind and water. Wind transport is usually only in the order of a few metres.” “Most of the really long-distance spread is by animals, vehicles, farm machinery, and in mud.” Spread by wind, water, vehicles and farm machinery.	Navie et al (1998) Parsons & Cuthbertson (2001)	MH
How far do they disperse?	In the majority of cases of long distance dispersal, achenes are transported on motor vehicles or machinery, on livestock, with crop and pasture seed, or in fodder. As a result, new infestations of the weed may appear thousands of kilometres from the nearest plants.” It is quite possible that many propagules will disperse more than one kilometre.	Navie et al (1998)	H

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