Invasiveness Assessment - Monto vetiver (Vetiveria zizanioides) 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 Monto vetiver.

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: Monto vetiver
Scientific name: Vetiveria zizanioides

Question	Comments	Rating	Confidence
Establishment
Germination requirements?	Monto vetiver grass is regarded as sterile (Hopkins, 2002) and requires direct human intervention for vegetative spread (Truong, 2000). New populations can be established from propagules that have been deliberately split from the crown of a mature plant (Truong, 2000). Newly planted slips sometimes wash out and establish themselves down the slope and on shallow soils, and runoff may wash plants away (NRC, 2003) but these propagules were originally directly derived from human intervention. The plant requires specific factors that are not part of an annual cycle to establish by vegetative propagules.	L	MH
Establishment requirements?	Is not tolerant of shading and establishes best in open areas (Truong, 2000). The plant requires open space to establish.	ML	MH
How much disturbance is required?	For establishment to occur, the plant needs major disturbance. It is only established by human cultivation (Truong, 2000). It is also intolerant of competition at the establishment stage. Weed control, especially of broadleaved species, is recommended until the plant is established, due to Monto vetiver being intolerant of shade (Truong & Creighton, 1994). The plant requires initial and ongoing disturbance to establish.	L	MH
Growth/Competitive
Life form?	Grass species (Truong, 2000).	MH	MH
Allelopathic properties?	Cropping species are reported to easily grow right up to vetiver hedges without significant decrease in yield (Truong, 2000) and native species can establish within vetiver hedges (Chelard, 2003). It appears that in drought years, vetiver may compete with the crop for moisture, however the row immediately beside the vetiver only seems to be affected (Slinger, 2004). This evidence suggests that the decrease in yield is due to the competitive ability of vetiver, rather than allelopathy. No evidence for allelopathy was found, and is unlikely to be allelopathic, given the ability of a range of other species to grow beside and within Monto vetiver hedges.	L	MH
Tolerates herb pressure?	Old growth is often considered unpalatable, however new growth is palatable to cattle, sheep, horses and wallabies. As the growing point is below the soil surface, consumed foliage is able to regrow quickly (Truong, 2000; Truong & Creighton, 1994). In its native range, cattle and buffalo grazing it kept it in check (Greenfield, 1989). Consumed, but not preferred, and able to recover.	MH	MH
Normal growth rate?	It has the high growth rate of a C4 grass species; equal to that of sugarcane and slightly more than maize (Vieritz et al, 2003), which are fast-growing crop species. However, it is also reported as very slow growing, taking up to 25 years for a clump to grow from 0.3 m to 3 m wide and is intolerant of shade, requiring broadleaf weed control for the first year (Truong, 2002; Truong & Creighton, 1994). The plant appears to have a rapid vertical growth rate that will equal or exceed most other grass species, however, it is slow to spread horizontally and appears not to compete well with broadleaved species. Exceeds the growth rate of most other species of the same life form.	H	MH
Stress tolerance to frost, drought, w/logg, sal. etc?	Tolerant of waterlogging (Truong, 2000); able to establish and thrive under waterlogged conditions (Truong, 1997). Has a deep root system, which makes it tolerant of drought (Truong, 2000). Growth point below soil surface, which helps it tolerate fire, frost and grazing (Truong, 2000). Tolerant of pH as low as 3 and high as 10.5 (Truong, 2000). Highly tolerant of salinity, heavy metals and other pollution (Truong, 2000). Highly tolerant of salinity and also tolerant of waterlogging, drought, fire and frost.	H	MH
Reproduction
Reproductive system	Monto vetiver [regarded as a South Indian type] is regarded as functionally sterile, found in one field trial to have only produced one viable seed from 40,000 caryops [seed structures] (Hopkins, 2002) and in a series of field and glasshouse trials, to never produce seed (Truong, 2002). A nursery trial of some South Indian types [which may, or may not have included Monto strain] found sterile vetivers to have an average fertility rate of 1.2% (Tsai et al, 2004). The latter study also concluded that this sterility is due to self-incompatibility; that sterile cultivars are incapable of self-pollination. When the South Indian types from this study were pollinated by North Indian types, hybridisation produced almost 100% seed set [although, this group may or may not have included the Monto strain].	MH	MH
Number of propagules produced?	Monto vetiver is regarded as functionally sterile, found in field trials to have only produced one viable seed from 40,000 caryops [seed structures] (Hopkins, 2002). A nursery trial of some South Indian types [which may, or may not have included Monto strain] recorded an average of 20 fertile seeds per plant (Tsai et al, 2004). Less than 50 propagules are produced per flowering event.	L	MH
Propagule longevity?	Reproduction is by cultivation of vegetative propagules only (Truong, 2000).	L	M
Reproductive period?	Plants have been reported to persist for more than 40 years (Truong & Creighton, 1994). Pre-flowering plants can be broken up to planting slips of 2-3 tillers and new plants are able to be propagated from stem layering after 3 months (NRC, 2003). This suggests that vegetative reproduction is possible from plants that are less than one year old, which may reach more than 40 years of age.	H	MH
Time to reproductive maturity?	Monto vetiver is regarded as functionally sterile, found in field trials to have only produced one viable seed from 40,000 caryops [seed structures] (Hopkins, 2002). It is not reported outside of cultivation and reproduction is by deliberate cultivation of vegetative propagules only (Truong, 2000). Human intervention is required to reproduce this plant. It never reaches reproductive maturity of its own accord.	L	MH
Dispersal
Number of mechanisms?	Propagules are only capable of spread via deliberate human dispersal (Truong, 2000). Newly planted slips sometimes wash out and establish themselves down the slope and on shallow soils, and runoff may wash plants away (NRC, 2003) but these propagules were originally directly derived from human intervention.	ML	MH
How far do they disperse?	Newly planted slips sometimes wash out and establish themselves down the slope and on shallow soils, and runoff may wash plants away (NRC, 2003). Deliberate movement by human cultivation regularly transports propagules more than 1 km, as is the case in Queensland, where Monto vetiver has been established following roadworks from Byerstown Range to Split Rock, Black Mountains, Trevethan Creek Green Hills Cut and Archer Point (Hopkinson, 2002). If required, legislation could prevent deliberate human dispersal of this species, so consideration is limited to unintentional movement, which would only be over a short distance.	L	M

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