Invasiveness Assessment - Perennial ragweed (Ambrosia psilostachya) in Victoria (Nox)

Back | Table | Feedback

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 Perennial ragweed.

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)
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: Perennial ragweed
Scientific name: Ambrosia psilostachya

Question	Comments	Reference	Rating
Establishment
Germination requirements?	Reproduces from seed and vegetatively. “Seeds germinate in autumn and plants develop rapidly over winter and spring. Plants… redevelop from adventitious root buds in autumn.”	Parsons & Cuthbertson (2001)	MH
Establishment requirements?	In North America, A. psilostachya most commonly grows in grasslands, savannas and woodlands, while in Australia it occurs on semi-arid grasslands, and along roadsides, in uncultivated fields, vacant lots and waste places. “A buildup of 3 to 5 inches (8–13 cm) of grass mulch on a lightly grazed rangeland delayed western ragweed growth in the spring.” Requires access to direct light and rainfall in open situations.	Pavek (1992) Parsons & Cuthbertson (2001)	ML
How much disturbance is required?	In Australia, it occurs on semi-arid grasslands, and along roadsides, in uncultivated fields, vacant lots and waste places. Occurs in disturbed ecosystems.	Parsons & Cuthbertson (2001)	ML
Growth/Competitive
Life form?	Geophyte	Pavek (1992)	ML
Allelopathic properties?	“Extracts from aerial growth are allelopathic, inhibiting germination and early seedling growth of several plant species.” “Western ragweed root exudate significantly inhibited the formation of nodules on legume roots, which decreases their ability to fix nitrogen.”	Parsons & Cuthbertson (2001) Pavek (1992)	MH
Tolerates herb pressure?	“It is not grazed by stock.” “The foliage and stems contain cinnamic acid and sesquiterpene lactones that deter herbivores.” But, in the U.S., it is a moderately important food source for ungulates. May be eaten by cattle and horses.	Parsons & Cuthbertson (2001) Pavek (1992)	MH
Normal growth rate?	“Perennial ragweed is a strongly competitive plant, often growing densely to the detriment of crop and pasture.” Rapid growth rate.	Parsons & Cuthbertson (2001)	H
Stress tolerance to frost, drought, w/logg, sal. etc?	“Aerial stems are killed by frost. Western ragweed is not drought tolerant.” Roots are not affected by frost, and the deeper set roots are not affected by fire.	Pavek (1992)	ML
Reproduction
Reproductive system	Reproduces vegetatively and sexually.	Parsons & Cuthbertson (2001)	H
Number of propagules produced?	No data available on seed production. From available photographs it appears that each plant would produce < 1,000 seeds. Fruits are achenes (single seed).	Parsons & Cuthbertson (2001)	ML
Propagule longevity?	“…seeds are able to survive many years in the soil, as is demonstrated by the reappearance of a patch of perennial ragweed ate Speed, Victoria, several years after all existing plants had been eliminated.” More than 25% of seeds survive 5–10 years in soil.	Parsons & Cuthbertson (2001)	ML
Reproductive period?	“Differing sets of seral stages have been suggested for secondary succession in prairie ecosystems, and western ragweed has been reported to occur in all of them and in climax communities. In old field succession, western ragweed was present as a principal forb in stands aged 0–5 years and was present with 4 to 15 percent cover after 23 to 29 years.” It appears that A. psilostachya is long lived.	Pavek (1992)	H
Time to reproductive maturity?	“Once seeded into an area, western ragweed may not set fruit until the second year.” Produces seed between 1 and 2 years after germination. However, new growth from roots will occur annually.	Pavek (1992)	MH
Dispersal
Number of mechanisms?	“Perennial ragweed spreads widely because the fruit is well adapted to tangle in wool and stick to furred animals, clothing, bags and other fibrous materials. Spread also occurs when the seeds, n mud, stick to animals, farm machinery and vehicles of all kinds. It is also commonly spread when contaminated soil and gravel are moved during road grading and road-making, and when such soil is used as garden topdressing.” Cultivation can spread root fragments that grow to new plants.	Parsons & Cuthbertson (2001)	MH
How far do they disperse?	Dispersal due to road grading and road-making, removal of soil could spread propagules more than 1 km, but most dispersal is likely to be less than this.	Parsons & Cuthbertson (2001)	MH

Feedback

Do you have additional information about this plant that will improve the quality of the assessment?
If so, we would value your contribution. Click on the link to go to the feedback form.

Page top