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Invasiveness Assessment - False yellowhead (Dittrichia viscosa) 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 False yellowhead.

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: False yellowhead
Scientific name: Dittrichia viscosa

Question
Comments
Rating
Confidence
Establishment
Germination requirements?‘Germination generally takes place following rainfall and can be quite prolific when fire or mechanical disturbance create bare ground’ (CRC for Australian Weed Management 2003). Opportunistic germinator.
H
M
Establishment requirements?Requires light to establish (Doussi & Thanos 1997).
ML
H
How much disturbance is required?‘ .. occasionally found in swamps but mainly occurs in highly disturbed areas such as roadsides, railway lines, fire breaks and walking trails ’ (CRC for Australian Weed Management 2003). Can establish in minor disturbed natural ecosystem.
MH
M
Growth/Competitive
Life form?Perennial soft-wooded shrub (CRC for Australian Weed Management 2003). Life form – other
L
M
Allelopathic properties?‘.. known to release substances that inhibit the germination of nearby plants’ (CRC for Australian Weed Management 2003). Allelopathic properties seriously affecting some plants.
MH
M
Tolerates herb pressure?Known to be toxic to stock (CRC for Australian Weed Management 2003). Favoured by heavy grazing as not eaten by animals/ insects.
H
M
Normal growth rate?Insufficient documented evidence to determine growth rate.
M
L
Stress tolerance to frost, drought, w/logg, sal. etc?‘ ..can grow and flower in saline conditions’. Has been found in swamps – tolerant to waterlogging (Curadi et al 2005). May be susceptible to drought and / or frost but insufficient information.
M
L
Reproduction
Reproductive systemReproduces by seed only. Not known if self or cross-pollination or both (CRC for Australian Weed Management).
L
M
Number of propagules produced?‘.. a prolific seed producer’ (CRC for Australian Weed Management 2003). ‘By estimation a medium sized plant may produce an average of 600-700 flowers per year each giving rise to about 50 viable seeds’ (Mifsud 2005).
H
M
Propagule longevity?‘Seeds of the closely related stinkwort Dittrichia graveolens are viable for about three years’ (CRC for Australian Weed Management 2003). No documented evidence on viability of D. viscosa propagules.
M
L
Reproductive period?Perennial shrub. Plant produces viable propagules for more than 3 years (CRC for Australian Weed Management 2003).
MH
M
Time to reproductive maturity?Insufficient information to determine time to reach reproductive maturity.
M
L
Dispersal
Number of mechanisms?Spread by wind, water, attached to machinery (CRC for Australian Weed Management 2003). Very light wind dispersed seeds.
H
M
How far do they disperse?‘Seed dispersal is aided by the ‘pappus’ .. which catches the wind and can assist flotation’ (CRC for Australian Weed Management 2003). Very likely that some propagules will disperse greater than 1 km.
H
M


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