Quick Facts

Quick facts

• Johnson Grass (Sorghum halepense) is a perennial tussock forming grass growing to 2 m high.
• It is a common weed found throughout Australia along roadsides, edges of creeks and in crops and pastures.
• It spreads mostly by seed but also from rhizomes.
• It causes severe crop losses due to direct competition, chemical inhibition of the growth of other plants and by acting as a host to crop pests and diseases. It can also be toxic to livestock.
• An integrated approach to control of Johnson Grass is the most likely to be effective, including chemical control, grazing, mowing, cultivation, crop rotation and use of competing crops.

What Does It Look Like?

What is it?

Johnson Grass (Sorghum halepense) is a tussock forming perennial grass growing to 2 m high, with upright stems arising from a creeping, branched, purple-spotted, scaly underground stem (rhizome). The leaves are more or less hairless, 20–50 cm long and 0.5–2 cm wide, with a ragged membranous structure called a ligule at the junction of the leaf-sheath and blade. The leaves are flat, with a prominent mid-rib and roughened margins (Paterson 1992; Parsons & Cuthbertson 2001).

The seed-head is 10–35 cm long, pale green to purplish, with loosely spreading branches and branchlets which bear the flower clusters (spikelets). Often there are a few hairs at the junction of these branches. The clusters are arranged in pairs or triplets at the ends of the branchlets and one of each pair or triplet is unstalked and fertile and the others are stalked and sterile. The fertile cluster is ovoid (egg-shaped), hairy, 4.5–5.5 mm long and often with a bent bristle 1–2 cm long. The sterile clusters are narrower and 5–7 cm long (Paterson 1992; Parsons & Cuthbertson 2001). There are about 35–350 clusters in each flowering structure. (Howard 2004). The seeds are reddish brown to black, egg-shaped, 3–4 mm long and finely lined on the surface (Paterson 1992; Parsons & Cuthbertson 2001).

For further information and assistance with identification of Johnson Grass contact the herbarium in your state or territory.

Flower colour

Purple, Green

Growth form (weed type/habit)

Grass

Where it currently grows? Preferred habitat

Johnson Grass occurs in tropical to temperate regions in wetter areas and is a common weed along roadsides and edges of creeks and in crops and pastures (Parsons & Cuthbertson 2001; Cotton Catchment Communities CRC 2007)

Are there similar species?

Johnson Grass is easily confused with other Sorghum species, especially Columbus Grass (Sorghum x almum). The flower clusters and seeds are very difficult to tell apart in mixed samples. The Johnson Grass cluster has a more long-pointed shape than that of Columbus Grass but as clusters are frequently found with broken ends, the difference is not always apparent (Scher 2005). Columbus Grass has a slightly larger seed than Johnson Grass but this difference is usually masked by the normal range of sizes in biological populations (Parsons & Cuthbertson 2001).

Why Is It A Weed?

What are its impacts?

Agriculture: Johnson Grass is considered to be one of the ten worst weeds in the world (Parsons & Cuthbertson 2001; Washington State NWCB Undated). It causes severe crop losses due to direct competition, chemical inhibition of the growth of other plants and by acting as a host to crop pests and diseases (Parsons & Cuthbertson 2001) It readily invades arable land, especially in areas of high summer rainfall, and has seriously reduced crop yields in New South Wales and Queensland (Parsons & Cuthbertson 2001). It is also a host for the Sorghum Midge (Contarinia sorghicola), as well as the aphid-transmitted sugarcane mosaic virus which causes dwarf mosaic disease in Maize and Sorghum. It also provides a pollen contaminant of nearby cultivated Sorghum (Sorghum bicolor) (Cotton Catchment Communities CRC 2007).

Johnson Grass is potentially toxic to livestock. It provides useful forage but at certain developmental stages or under some adverse environmental conditions, Johnson Grass may form cyanogenetic glycosides that can poison livestock. The glycosides are present in sorghum at low levels most of the time. However, acute poisoning is most likely to occur when the plant is growing fast, such as when it rains after a dry spell, and in damp or overcast conditions, or when hungry animals eat a large amount of fresh moist grass. The glycoside when metabolised releases hydrogen cyanide into the blood stream. Cattle tend to be more susceptible than sheep (Hawkins & Lacey 2001; Howard 2004). Other reports state that Johnson Grass is most toxic to animals when it is under stress from frost, drought, when it has been sprayed with herbicide, or has been trampled, especially in young leaves and stems (Howard 2004; Cotton Catchment Communities CRC 2007). Johnson Grass may also sequester selenium (or other elements that are toxic at high doses) when growing in soils with high concentrations of toxic elements. In the Dead Sea area of Jordan, for example, selenium concentrations in Johnson Grass samples were high enough to poison livestock. Prolonged consumption of fresh Johnson Grass can cause nitrate poisoning in animals.

Native ecosystems: South of 32°S in Australia, where rainfall is lower and more evenly spread, Johnson Grass is restricted to roadsides, fence lines, waste places and channel edges; however, it will invade native vegetation, particularly wetlands, from adjoining arable lands (Parsons & Cuthbertson 2001).

Urban environments: Johnson Grass presents a safety hazard on roads by restricting visibility on curves and corners (Parsons & Cuthbertson 2001; Washington State Noxious Weed Control Board Undated).

How does it spread?

Johnson Grass spreads mostly by seed which is small, lightweight and easily dispersed by wind and water. Run-off from rain carries seed downhill into creeks and storm drains. Animals carry the grass seed on their skin and fur and the seed passes through the digestive tracts of animals and birds relatively intact. Seed may also be spread as a contaminant in agricultural produce and in mud sticking to machinery and vehicles (Parsons & Cuthbertson 2001; Brown & Brooks 2002).

Johnson Grass produces many seeds under favourable growing conditions – a single plant may produce 80,000 or more seeds in one growing season (Howard 2004) which can build up a soil seed bank. Seed can remain dormant and viable for several years, although most soil-stored seeds germinate in their 1st or 2nd year. In California, 5-year-old buried seed showed greater than 50% viability, but by age 6, viability dropped to 2% (Brown & Brooks 2002; Howard 2004).

Johnson Grass also propagates vegetatively. The production of outgrowths from the tussocks (tillers) or shoots from the underground stems (rhizomes) is responsible for each tussock's expansion. The outgrowths and underground stems may break off when disturbed, take root elsewhere and give rise to new plants (Parsons & Cuthbertson 2001; Brown & Brooks 2002). Underground stems are also somewhat drought-resistant, remaining viable after drying to 40% of initial harvest weight (Howard 2004).

What is its history in Australia?

Johnson Grass was probably introduced to Australia as a potential fodder plant in the middle of the 1800s and is recorded as being grown in the Adelaide Botanic Gardens in 1871. It was first recorded as naturalised at Gloucester, New South Wales in 1883 (Parsons & Cuthbertson 2001).

How To Manage It?

Best practice management

Control of Johnson Grass is difficult because of its ready regeneration from underground stems. Integrated control programmes, in which crop rotation, cultivation, competing crops and chemical measures are combined, usually give the best results (Parsons & Cuthbertson 2001).

Non-chemical control: For small infestations, hand-pulling Johnson Grass usually leaves rhizome pieces behind in the soil, stimulating sprouting, so best results are obtained in early spring when soil in moist and rhizomes are least likely to break. Repeated solarization treatments (using a clear polyethylene tarp to trap solar heat in the soil) can also be used (Parsons & Cuthbertson 2001; Howard 2004).

In cropping situations a consistent tillage program may provide effective control. Flooding for 3–6 weeks in early spring, before underground stems sprout, can also work. Replacing open irrigation ditches with culverts or pipes helps prevent reinfestation. Geese are sometimes used for Johnson Grass control in croplands although they only prefer young shoots, and do not graze tussocks over about 7 inches (18 cm) in height.

Fire: Fire may be a useful as long as it is used in conjunction with follow-up herbicide treatments to control underground stem sprouts. Spring burning without further control treatments is not recommended for controlling Johnson Grass, as it is likely to promote sprouting (Howard 2004). Similarly, heavy grazing over two or more years reduces Johnson Grass by depleting underground stem reserves. Rhizome development is greatly reduced when plant height is kept to about 30 cm. Best control is offered when herbicide or winter ploughing treatments follow grazing treatments (Howard 2004). Repeated, close mowing has the same inhibitory effect on growth as grazing (Parsons & Cuthbertson 2001; Howard 2004).

Chemical control: The most effective chemical control of Johnson Grass involves using systemic herbicides that ensure the active chemicals reach the underground stems. A single application of herbicide generally does not control large infestations, and follow-up measures are needed for long-term control (Howard 2004). Spraying during the first two weeks of season's growth is recommended (Brown and Brooks 2002). Soil disturbance should be avoided. Follow up with spot spraying and seedling control is important. Different ecotypes may show differential response to herbicides (Howard 2004).

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au 

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Johnson Grass seeds germinate in spring and early summer. Three weeks after emergence, the growth rate of the leaves increases rapidly. Underground stem growth continues slowly until first flowering which occurs seven weeks after emergence and then accelerates. There are two flowering periods in early summer and late summer to autumn. New shoots from underground stems have a similar growth pattern but they emerge earlier in the season and grow faster than seedling plants (Parsons & Cuthbertson 2001). Resources are allocated to rhizomes at the expense of seeds under poor growing conditions (Howard 2004).

Johnson Grass is frost sensitive and is burnt off over winter, but plants readily re-establish in spring from last-year or primary underground stems which produce new, secondary and tertiary underground stems (Cotton Catchment Communities CRC 2007). This growth slows or stops around the time of flowering, then resumes with seed head development and peaks at seed ripening when a single plant may produce 60–90 m of underground stem. Growth and carbohydrate accumulation continues until late autumn, and then goes dormant over winter. The original primary underground stems die each autumn (Howard 2004).

Where Is It Found?

Which states and territories is it found?

NSW, NT, QLD, SA, TAS, VIC, WA

What areas within states and territories is it found?

Johnson Grass is now widespread throughout New South Wales on the North Coast and Central Coast, the Tablelands, the Western Slopes of the Great Dividing Range and the irrigation districts. It is scattered throughout the farming areas of Queensland and the irrigation districts of Victoria and South Australia. In Western Australia, it is becoming a problem in the East Kimberley irrigation district, the Geraldton area and the lower south west (Parsons & Cuthbertson 2001). It is also has a scattered distribution in other parts of these states and the Northern Territory, Tasmania and the Australian Capital Territory (Navie 2004; AVH 2008).

Where does it originate?

The smaller, narrow-leaved ecotype of Johnson Grass found in Australia originally comes from the Mediterranean. It is widely distributed throughout the Near East, North Africa and southern Europe and is naturalised in North and South America, Hawaii, New Zealand, Australia and nearby islands (Parsons & Cuthbertson 2001). A more robust tropical type extends from southern India to western Pakistan (Parsons & Cuthbertson 2001).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, NT, WA

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Sorghum halepense

Other scientific names (synonyms)?

• Andropogon halepensis (L.) Brot.
• Andropogon miliaceus Roxb.
• Andropogon sorghum f. muticus Hack.
• Andropogon sorghum subsp. halepense (L.) Hack.
• Andropogon sorghum var. halepense (L.) Hack.
• Holcus halepensis L.
• Sorghum halepense f. muticum (Hack.) C.E.Hubb.
• Sorghum miliaceum (Roxb.) Snowden

Does it have other known common name(s)?

Aleppo, Aleppo Grass, Barool, Baru Grass, Cubagrass, Egyptian Millet, Evergreen Millet, False Guineagrass, Maidencane, Neansgrass, St. Mary's Grass, Syriagrass