Grader grass (Themeda quadrivalvis)

Assessment ID: 1068
Jurisdiction: North Territory
Methodology: Northern Territory Weed Risk Management System - terrestrial
Management area: Darwin and Katherine Regions

Notes: 

Status: PUBLISHED
Last updated: 21/8/2025 4:56:01 pm AEST

Questions answered: 39 / 47

Weed Risk: 239.69 (Very high)
   Invasiveness (raw/adjusted): 8.00 / 6.664
   Impacts (raw/adjusted): 10.00 / 5.260
   Potential distribution (raw/adjusted): 13.00 / 6.838

Feasibility of Control: 34.95 (Low)
   Control costs (raw/adjusted): 5.00 / 4.545
   Current distribution (raw/adjusted): 1.00 / 1.000
   Persistence (raw/adjusted): 10.00 / 7.690

Result: Targeted control (including biocontrol), protect priority sites

Invasiveness

A1. What is the ability of the plant to establish amongst intact native environments?
Answer: Very High

Comments: 
Can invade native pastures or grassland (Smith 2002).

Listed as a ‘naturalised exotic; naturalised in native plant ecosystems’, and a severe threat to both natural and pastoral areas in the Top End (Smith 2001).

This study of pastures in central Queensland in the late 1970s showed that most grader grass was found in native pasture (rather than sown grass or legume pastures) (Anderson et al. 1983).

In the Mackay area, on the central Queensland coast, grader grass inhabits eucalypt open forest as well as disturbed areas such as roadsides or cleared vegetation (Batianoff & Franks 1998).

Primarily a weed of overgrazed pastures or disturbed areas such as roadsides (Groves 1991).

Capable of invading both native and improved pastures, competing with useful pasture species in over-utilised or disturbed areas (Pitt 1998).

Often occurring as a weed in moist disturbed areas such as road verges, railway enclosures, and waste places, from where it invades degraded native grasslands and sown pastures as well as some arable areas (Parsons & Cuthbertson 2001).

A2. What is the reproductive ability of the plant?

(a) Time to seeding
Answer: 1 year or less

Comments: 
Flowering occurs within 5 to 6 weeks of germination, with ripe seed being present at 10 weeks (Bishop 1981, Mitchell & Hardwick 1995, Parsons & Cuthbertson 2001).

Ripe seed appeared at 9 weeks in irrigated potted plants grown in Charters Towers, north Queensland (A. Keir [NT Weeds Management Branch] personal obs.).

(b) Annual production of viable seed /m2 or /plant
Answer: High

Comments: 
This study recorded a germinable seed bank of >10 seeds per 1-inch diameter soil core under dense infestations. This equals approximately 20 000 seeds per m2. The same study also suggests that viability of seed in the soil declines to almost zero within 15 months, so this number represents at most two year’s seed production (Sillar 1969).

Seeds are produced in prolific numbers (Smith 2002).

States that seed production is not ‘prolific’ (less than 2000 per m2) (Pacific Islands Ecosystems at Risk 2006).

(c) Vegetative reproduction
Answer: None

Comments: 
No reproduction by vegetative fragmentation (Pacific Islands Ecosystems at Risk 2006).

A3. Do propagules of the plant have properties that allow them to be dispersed long-distance by natural means?

(a) Flying animals (birds, bats)
Answer: No

Comments: 
Propagules not bird dispersed (Pacific Islands Ecosystems at Risk 2006).

(b) Other wild animals
Answer: Yes

Comments: 
No specific information available.

(c) Water
Answer: No

Comments: 
Grader grass has poorly developed mechanisms for the natural movement of seeds over long distances (Bishop 1981).

Seeds… do not normally travel great distances by natural means (Smith 2002).

Grader grass seeds are not adapted in any way for dispersal by wind or water. The major proportion fall close to the parent plant… (Parsons & Cuthbertson 2001).

(d) Wind
Answer: No

Comments: 
Grader grass has poorly developed mechanisms for the natural movement of seeds over long distances (Bishop 1981).

Seeds… do not normally travel great distances by natural means (Smith 2002).

Grader grass seeds are not adapted in any way for dispersal by wind or water. The major proportion fall close to the parent plant… (Parsons & Cuthbertson 2001).

A4. How likely is long-distance dispersal by human-assisted means?

(a) Deliberate spread by people
Answer: Unlikely

Comments: 
Used to produce hay in native India (Thaware & Jadhav 1989).

In Madhya Pradesh, India, it has some fodder value and is used for thatching (Skerman & Riveros 1990).

Deliberate planting in the NT unlikely as it is a declared species (A. Keir [NT Weeds Management Branch] personal obs.).

(b) Accidentally by people and vehicles
Answer: Common

Comments: 
Most seeds are transported over long distances through introduced means, e.g clothing, soil, machinery (Parsons & Cuthbertson 2001).

New infestations over long distances usually result from the transport of seed by introduced carriers such as vehicles, machinery or human activities (Bishop 1981).

(c) Contaminated produce
Answer: Common

Comments: 
Spread as a contaminant in pasture seed or hay (Parsons & Cuthbertson 2001, Smith 2002, Wheaton 1994).

It is spread by removal of soil, contaminated fodder, crop and pasture seed (Mitchell & Hardwick 1995).

Grader grass appears to have been introduced to Australia in contaminated straw packing or stuffing (Bishop 1981, Chapman 1969).

Several authors report it being introduced into the NT in 1967/68 as a contaminant in pasture seed (Groves 1991, Miller & Harrison 1982, Parsons & Cuthbertson 2001, Pitt 1998, Smith 2002).

This paper reports an accidental introduction of grader grass into Kansas, USA as a contaminant in imported birdseed. The authors then examined a number of commercial thistle seed samples and found all to be contaminated with T. quadrivalvis seed (Towne & Barnard 2000).

(d) Domestic/farm animals
Answer: Occasional

Comments: 
No specific information available.

Impacts

B1. What is the plant's competitive potential?
Answer: High

Comments: 
This study compared germination of 19 common grass species of the seasonally dry tropics of northern Australia, including grader grass. It showed that grader grass germinated the fastest of these species, which could give it a significant competitive advantage during establishment (McIvor & Howden 2000).

Grader grass is capable of competing with useful pasture species in heavily grazed or disturbed areas (Wheaton 1994).

Forms virtual monocultures, excluding almost all other plants’ and prevents seedling establishment by strangling/choking seedling plants (Earthworks 2003).

The author states that ‘it has been demonstrated that seeds will not germinate under shaded conditions’ (Chapman 1969).

B2. What is the plant’s potential to modify the existing fire behaviour and alter the fire regime?
Answer: Some potential

Comments: 
Sometimes comparatively unpalatable introduced grasses invade grazed sites and the dry season fires are then usually more frequent and of higher intensity. The authors give the example of Themeda quadrivalvis near Mareeba, north Queensland (Stocker & Mott 1981).

Observed in the Thuringowa region of north Queensland to generate large fuel loads (Earthworks 2003).

In a grass species evaluation experiment at Mackay in 1978, grader grass yields (as a weed) of over 3000 kg per ha were recorded after 3 months growth (Bishop 1981).

In reference to grader grass growing in cane crops in central Queensland, the author states that it does not burn well in the winter months, but will burn completely in the dry summer (Chapman 1969).

Grader grass causes a fire hazard once it has matured and died (Bishop 1981).

B3. What is the plant’s potential to restrict the physical movement of people, animals, vehicles, machinery and/or water?
Answer: Low

Comments: 
No specific information available.

B4. What is the plant’s potential to negatively affect the health of animals and/or people?
Answer: Low

Comments: 
Cattle will graze on grader grass when it is young (A. Cameron [DPIF Pastures] 2015, pers comm. 19 November).

Although it can be unpalatable, grader grass is not harmful to stock (Bishop 1981).

B5. Does the plant potentially have negative effects on natural and cultural values?

(a) Reducing habitat quality for native animals?
Answer: Medium

Comments: 
No specific information available.

(b) Threatened species or communities
Answer: More than one

Comments: 
No specific information available.

(c) Sites of natural or cultural significance
Answer: More than one

Comments: 
Causes a significant reduction in diversity in native plants (Smith 2002).

B6. Is the plant presumed to have negative effects on environmental health?

(a) Soil chemistry/stability
Answer: No

Comments: 
No specific information available.

(b) Water quality
Answer: No

Comments: 
No specific information available.

(c) Hydrology
Answer: No

Comments: 
No specific information available.

Potential distribution

C1b. What is the Climatch suitability score (which indicates the proportion of the NT environment that is suitable for the plant)?
Answer: 9

Comments: 
Grader grass is native to India where it occurs as a component of perennial native pastures receiving an annual rainfall of 375 to 2000 mm. In that country, best development occurs with 500 to 875 mm rainfall (Bishop 1981).

It is a predominant species of grasslands on well-drained lateritic soils in a region of India receiving 3200 mm average annual rainfall (Thaware et al. 1989).

In this region, it also persisted in an above average year of nearly 4500 mm (Thaware et al. 1989).

In its current Australian distribution, average annual rainfall ranges from about 450 mm in inland regions to more than 2000 mm on the north-eastern tropical coast (Keir & Vogler 2006).

C2. How many broad habitat types in the NT will the plant potentially naturalise in (up to 5)?
Answer: Two

Comments: 
The two broad vegetation types in the Northern Territory that Themeda quadrivalvis will potentially naturalise in are tropical riparian areas and tropical open forests/savannah woodlands (N. Cuff [NT Herbarium] 2015, pers comm. 29 September).

Tropical riparian areas -and Tropical open forests/savanna woodlands (NT WRMS Technical Committee 2007).

C3. What is the potential of the plant to occur throughout its favoured habitat in the NT (as identified in question 2)?
Answer: Some

Comments: 
Tropical open forests/savanna woodlands is the most favoured habitat, on the basis that it needs disturbance to establish (NT WRMS Technical Committee 2007).

Control costs

A1. How detectable is the weed?

(a) Distinguishing features
Answer: Sometimes distinct

Comments: 
The two are most reliably distinguished by the size of the spikelets and the native of the hairs on their seeds heads. Grader grass has smaller spikelets (4-7 mm long) and has conspicuous, tubercle-based hairs (distinct, bulbous-based bristles) on the seed head, while kangaroo grass spikelets are 8-14 m long are either hairless or have fine hairs with only a slightly bulbous appearance (Bishop 1981, Blake 1969, Keir & Vogler 2006, Parsons & Cuthbertson 2001, Pitt 1998, Wheaton 1994, Wheeler 1992).

Erect, tufted annual or perennial grass to 2 m tall, often growing in dense patches. Mature plants golden in appearance. Stems robust. Seed with bent awns at the end, enclosed in leafy bracts (Smith 2002).

The grass is similar in appearance to the native perennial Kangaroo Grass (Themeda australis). Kangaroo grass is generally smaller (usually growing to less than 1 m in height) and has a brown rather than golden appearance when mature (Keir & Vogler 2006, Parsons & Cuthbertson 2001, Pitt 1998).

Looks similar to thatch grass (Hyparrhenia rufa). Thatch grass can be distinguished from grader grass by having finer stems, more tilers per plant a more open and more erect seed-head (Bishop 1981).

(b) Active growth period
Answer: 4-8 months

Comments: 
Grader grass usually behaves as an annual (Bishop 1981, Sillar 1969), although Harden (1993) and Smith (2002) suggested it may also survive as a perennial but did not describe the situation where this would occur (Bishop 1981, Harden 1993, Keir & Vogler 2006, Sillar 1969, Smith 2002).

(c) Height at maturity
Answer: 0.5 - 2 m

Comments: 
Grass to 2m tall (Smith 2002).

Plant height depends on the conditions but ranges from around 50 cm to over 2 m on roadsides and newly established pasture areas (Bishop 1981).

A tufted annual grass to 2 m or more in height (Wheaton 1994).

A2. What is the general accessibility of infestations at the optimum treatment time?
Answer: Medium

Comments: 
Prominent along roadsides and in disturbed areas (Smith 2002).

Often occurring as a weed in moist disturbed areas such as road verges, railway enclosures, and waste places, from where it invades degraded native grasslands and sown pastures as well as some arable areas (Parsons & Cuthbertson 2001).

Primarily a weed of overgrazed pastures or disturbed areas such as roadsides (Groves 1991).

Accessibility for Grader Grass in the Darwin Region is reasonable in the early wet with the assumed equipment undertaking control in January with a follow up in early February depending on the wet season. It is also assumed that the infestations are well known as identification this early is difficult (P. Jeffery [Specialist Weed Control] 2006, pers comm).

I would suggest that gamba grass has medium general accessibility, as you often need equipment such as quads to reach the grass in woodland areas (G. McSkimming [Coomalie Weed Control] 2006, pers comm).

A3. How expensive is control of the weed in the first year of targeted control, for an infestation that has reached maximum weed density?

(a) Chemical costs
Answer: Medium

Comments: 
Two primary treatments, each at a cost of: 
4.2kg Glyphosate Bi Dry + 1.2L Uptake and 600L water per ha = ~ $42/ha. 
One follow up treatment at a cost of: 
2.1kg Glyphosate Bi Dry + 0.6L Uptake and 300L water per ha = ~ $21/ha. 
Total: $105 per hectare. 
[Note: This would place Grader grass control in the Medium ($100- 250/ha) chemical cost category. However, note that the cut off for the Low (<$100/ha) category is $100] (P. Jeffery [Specialist Weed Control] 2006, pers comm).

(b) Labour cost
Answer: Medium

Comments: 
Two primary treatments, each at a cost of: 
1 hr x 2 operators per Ha =~ $105. 
One follow up treatment at a cost of: 
1/2hrs x 2 operators per Ha =~ $52.50. 
Total: $262.5 per hectare. 
[Note: This would place Grader grass control in the High ($200-500/ha) labour costs category. However, note that the cut off for the Medium ($100-250) category is $250] (P. Jeffery [Specialist Weed Control] 2006, pers comm).

(c) Equipment cost
Answer: Medium

Comments: 
Two primary treatments, each at a cost of: 
1 x 4WD + QuikSpray @ 1 hrs = ~ $37.50. 
One follow up treatment at a cost of: 
1 x 4WD + QuikSpray @ 1/2 hrs = ~ $19. 
Total: $94 per hectare. 
[Note: This equipment would place Grader Grass control in the Medium equipment costs category] (P. Jeffery [Specialist Weed Control] 2006, pers comm).

A4. What is the general community perception of this weed within the region?
Answer: Low

Comments: 
No specific information available.

Current distribution

B1. What is the current pattern of the species’ distribution across the weed management region?
Answer: Widespread

Comments: 
No specific information available.

Persistence

C1. How long will it take to reach the maintenance period?
Answer: High

Comments: 
The soil seedbank appears to be relatively short lived (McIvor & Howden 2000, Sillar 1969, Keir & Vogler 2006).

If germination and establishment can be prevented for one season, the problem can be greatly reduced (Anonymous 1967 in Keirs & Vogler 2006, Sillar 1969).

Once an area has become infested [with grader grass] weak points in the plant’s life cycle can be targeted to achieve control. Control should therefore aim to prevent flowering and seeding by maintaining competitive pastures which will limit germination and reduce establishment the following year (Keir & Vogler 2006, Parsons & Cuthbertson 2001, Pitt 1998).

C2. What is the minimum time period for reproduction of sexual or vegetative propagules?
Answer: <1 growing season

Comments: 
Flowering occurs within 5 to 6 weeks of germination, with ripe seed being present at 10 weeks (Bishop 1981, Mitchell & Hardwick 1995, Parsons & Cuthbertson 2001).

Ripe seed appeared at 9 weeks in irrigated potted plants grown in Charters Towers, north Queensland (A. Keir [NT Weeds Management Branch] personal obs).

C3. What is the maximum longevity of sexual or vegetative propagules?
Answer: <2 years

Comments: 
This study suggests that viability of seed in the soil declines to almost zero within 15 months, so this number represents at most two year’s seed production (Sillar 1969).

A germinable seed bank of over 20, 000 seeds per square meter can exist under dense infestations, but there appears to be a rapid decline in the viability of seed in the soil to almost zero with 15 months (Sillar 1969, Keir & Vogler 2006).

C4. What is the threat of reinfestation from outside the management region?

(a) Long-distance (>100m) dispersal by natural means
Answer: Rare

Comments: 
Grader grass seed is not easily spread by natural means (Keir & Vogler 2006).

Propagules not bird dispersed (Pacific Islands Ecosystems at Risk 2006).

Grader grass has poorly developed mechanisms for the natural movement of seeds over long distances (Bishop 1981).

Seeds… do not normally travel great distances by natural means (Smith 2002).

Grader grass seeds are not adapted in any way for dispersal by wind or water. The major proportion fall close to the parent plant (Parsons & Cuthbertson 2001).

Long distance dispersal occurs on fur or mud stuck to animals (Parsons & Cuthbertson 2001).

(b) Long-distance (>100m) dispersal by human means
Answer: Rare

Comments: 
Deliberate planting in the NT unlikely as it is a declared species (A. Keir [NT Weeds Management Branch] personal obs).

Most seeds are transported over long distances through introduced means, e.g clothing, soil, machinery (Parsons & Cuthbertson 2001).

New infestations over long distances usually result from the transport of seed by introduced carriers such as vehicles, machinery or human activities (Bishop 1981).

Spread as a contaminant in pasture seed or hay (Parsons & Cuthbertson 2001, Smith 2002, Wheaton 1994).

It is spread by removal of soil, contaminated fodder, crop and pasture seed (Mitchell & Hardwick 1995).

References

Anderson, E. R., Russell, F. J., Scanlan, J. C. & Fossett, G. W. (1983). Pastures under development in central Queensland. Part 1: Mackay region. Queensland Department of Primary Industries, Brisbane, Australia. Anonymous (1967). Agrostology Technical Annual Report 1967. Queensland Department of Primary Industries, Brisbane. Viewed in Keirs & Vogler (2006). Batianoff, G. N. & Franks, A. J. (1998). Weed invasion of the tropical Mackay coast, Queensland. Plant Protection Quarterly 13: 123-128. Bishop, H. G. (1981). Grader grass - a nuisance weed. Queensland Agricultural Journal 107: 235-239. Blake, S. T. (1969). Taxonomic studies and nomenclatural studies in the gramineae, No 1. Proceedings of the royal society of Queensland 80: 55-84. Chapman, L. S. (1969). Control of habana oat grass. Cane Growers' Quarterly Bulletin 33: 8-10. Earthworks. (2003). Revegetation strategy for the city of Thuringowa. Earthworks, Townsville. Groves, R. H. (1991). Weeds of Tropical Australia. In: Tropical grassy weeds, eds. F. W. G. Baker & P. J. Terry, pp. 189-196. C.A.B. International, Wallingford, U.K. Harden, G. J. (1993). Flora of New South Wales, Volume 4. New South Wales University Press, Sydney. Keir, A. F. & Vogler, W. D. (2006). A review of current knowledge of the weedy species Themeda quadrivalvis (grader grass). Tropical Grasslands 40: 193-201. McIvor, J. G. & Howden, S. M. (2000). Dormancy and germination characteristics of herbaceous species in the seasonally dry tropics of northern Australia. Austral Ecology 25: 213-222. Miller, I. L. & Harrison, P. G. (1982). Grader grass - a potential threat to Territory pastures. NT Rural News Magazine 7: 3-7. Mitchell, J. & Hardwick, G. (1995). Animal and weed pests of Cape York Peninsula, Cape York Peninsula Land Use Strategy. Office of the Co-ordinator General of Queensland, Brisbane, and Department of the Environment, Sport and Territories, Canberra. More references available on request from weedinfo@nt.gov.au.