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Invasiveness Assessment - Spiny emex (Emex australis) 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 Spiny emex.

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: Spiny emex
Scientific name: Emex australis

Question
Comments
Reference
Rating
Establishment
Germination requirements?“Seeds germinate at almost any time of year if soil moisture is adequate”.
P & C (1992)
H
Establishment requirements?Occurs in mostly ‘open habitats’. (See Habitats section).

“Grows best in the open rather than in the shade of other plants”.
(Gilbey and Weiss 1980)
ML
How much disturbance is required?Is an envil weed in “lowland grassland and grassy woodland”.

Serious weed of crops and pastures.
Carr et al (1992)
Weiss & Simmons (1979)
MH
Growth/Competitive
Life form?A semi prostrate annual herb.

Other.
P & C (1992)
L
Allelopathic properties?None described.
L
Tolerates herb pressure?Not readily eaten by stock.
P & C (1992)
MH
Normal growth rate?“It competes with cereal crops and pastures because it is fast growing”.
P & C (1992)
MH
Stress tolerance to frost, drought, w/logg, sal. etc?Tolerant of moisture stress.
P & C (1992)
Hawkes Bay RC (1995)
L
Reproduction
Reproductive systemReproducing by seed-male and female flowers separate on the same plant.
P & C (1992)
ML
Number of propagules produced?“Up to 1 100 seeds have been recorded on individual plants”.
P & C (1992)
MH
Propagule longevity?Fruit is long-lived in soil (>4 years). “On undisturbed areas, very little seed germinates after 2 years”.
P & C (1992)
L
Reproductive period?Forms dense monocultures, sometimes > 900 plants per sq. m.
P & C (1992)
H
Time to reproductive maturity?Germination mostly occurs in autumn/winter – flowering late winter/early summer – seed maturation spring and through summer.
P & C (1992)
H
Dispersal
Number of mechanisms?Fruit (with spines) attach to shoes, rubber tyres, feet of animals or containers of produce. Also contaminated fodder and water.
P & C (1992)
MH
How far do they disperse?Above mechanisms could transport seeds > 200 m.
MH


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