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Invasiveness Assessment - Annual ragweed (Ambrosia artemisiifolia) in Victoria

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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 Annual 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 - 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: Annual ragweed
Scientific name: Ambrosia artemisiifolia

Question
Comments
Rating
Confidence
Establishment
Germination requirements?Germination is combination of light and temperature and although usually germinates in spring, can germinate at other times of year if conditions are suitable (Parsons & Cuthbertson 2001, DNRM 2005).
MH
MH
Establishment requirements?Prefers dry, sunny grassy plains, along riverbanks, roadsides, disturbed soils, vacant lots and ruderal sites (Parsons & Cuthbertson 2001). Limited growth in shade.
ML
MH
How much disturbance is required?"Primarily a plant of disturbed open areas" occurs as weed of cultivated lands, stubble fields, old pastures, wastelands" (Parsons & Cuthbertson 2001).
ML
MH
Growth/Competitive
Life form?Annual herb (Parsons & Cuthbertson 2001) – life form –other.
L
MH
Allelopathic properties?Annual ragweed ‘produces allelopathic responses in several other weed and crop species .. strongly inhibit germination of onion, oats, Lolium spp. (Parsons & Cuthbertson 2001).
MH
MH
Tolerates herb pressure?Cattle eat annual ragweed in early stages. A variegated leaf beetle and stem-galling moth are used in biological control in Queensland with the moth ‘reducing ragweed populations and seed production in warmer areas’ (Parsons & Cuthbertson 2001).
ML
MH
Normal growth rate?Serious competitor with cereal crops and vegetables in early growth stage but poor competitor in well managed pastures and legume crops. Growth rate rapid depending on environment (Parsons & Cuthbertson 2001). Most often occurs in wasteland areas so score as Medium High.
MH
MH
Stress tolerance to frost, drought, w/logg, sal. etc?Due to the locations it can be found, it appears to have saline tolerance. Susceptible to frost and fire. Drought tolerant. Can be found in flood plains but no mention of ability to withstand waterlogging (Parsons & Cuthbertson 2001).
ML
MH
Reproduction
Reproductive systemWind pollinated. A ‘self-compatible species’ (Bassett & Crompton 1975 (cited in Genton, Shykoff & Giraud). Cross and self-pollination but cannot vegetatively reproduce (Parsons & Cuthbertson 2001).
ML
H
Number of propagules produced?Annual ragweed produces an average of 3000 seeds per year (Parsons & Cuthbertson 2001).
H
MH
Propagule longevity?Annual ragweed seeds can be viable for more than 40 years (Parsons & Cuthbertson 2001).
H
MH
Reproductive period?Annual plant (Parsons & Cuthbertson 2001).
L
MH
Time to reproductive maturity?Reaches maturity in 4-5 months (Parsons & Cuthbertson 2001).
H
MH
Dispersal
Number of mechanisms?Clings to sheep, furred animals, bags, clothing, water, contaminated gravel and soil (Parsons & Cuthbertson 2001).
MH
MH
How far do they disperse?Spreads ‘readily over long distances’. Hull provides buoyancy (Parsons & Cuthbertson 2001).

Seems likely that some of the propagules will disperse greater than 1 km.
H
MH


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