Johnson Grass

Sorghum halepense (L.) Pers.

Synonyms - Andropogon halepensis, Holcus halepensis, Sorghum bicolor ssp. halepense).

Similes. - Sorghum almum.

Family: - Poaceae.


Sorghum is from the Latin surrigo meaning to grow up referring to the tallness of some species or from the Latin surgum or suricum referring to Syrian corn.

Halepense is a combination of Allepo, a Syrian town and the Latin ense meaning from, and referring to the origin of the plant first described by Linnaeus.

Johnson grass refers to the man who introduced it to the USA around 1830, where it quickly established as a weed.

Other names:

Alleppo grass

Allepo Milletgrass

Barool (India)

Baru grass (Pakistan)

Evergreen Millet

Pangan (Indonesia)

Yah poeng (Thailand).


A tall, relatively hairless perennial grass with broad, long leaves with a prominent midrib underneath, jagged membranous ligule and erect stout stems arising from a creeping, rooting, scaly rhizome. It produces a purplish-brown pyramidal, seed head about 25 cm long in summer.






Blade - Flat, smooth, 150-700 mm long by 5-30 mm wide, parallel sided, pointed tip, obvious midrib on the lower surface. Edges are white, rough to touch and often wavy. Hairless except near junction with sheath which may be hairy. Rolled in the bud.

Ligule - Membranous and papery, 2-5 mm long, usually flat on top, jagged and fringed.

Auricles - None.

Sheath - Loose, broad, striped, ribbed. Hairless.


Slender to stout, erect, tufted, spreading, 500-1500 mm tall, occasionally to 3000 mm tall. Hairless apart from nodes which may be finely hairy. Lower nodes that are rooted are always hairy. Sometimes bent at the nodes. Arising from an extensive, creeping, rooting, white, reddish or purple spotted, scaly rhizome.

Flower stem -

Flower head:

Pale green to purplish, pyramidal panicle, 100-400 mm long by 50 to 250 mm wide. Compact to open and spreading. Often hairy at the nodes. Many, slender branches in rings or single, dividing into finer branches, bare at the base, jointed, angular, rough on the angles and hairy at the joints. Tips of the stalks cup shaped. Spikelet clusters(racemes) held close to panicle branches, 10-25 mm long, fragile, with pale hairs on the stalks and joints.


Spikelets - Usually in pairs on branches and group of 3 at the end. Two types; stalked and stalkless.

Stalkless one bisexual, jointed at the base, fall off easily, pale green or sometimes reddish, 4.5-5.5 mm long, almost pointed tip, awned or awnless, glossy.

Stalked spikelets male or sterile, pale green to reddish or purplish, narrowly egg shaped, 5-7 mm long, not shiny. Falls with stalkless spikelet.

Florets - 2 in each spikelet. Lower one reduced to an empty lemma. Upper one bisexual in the stalkless spikelet.

Glumes - On stalkless spikelet, leathery, stiff, narrowly egg shaped, all about the same size, 4.5-5.5 mm long by 2-3 mm wide. Short pale hairs becoming hairless and shiny with age. Lower glume has 5-9 ribs near tip. Upper glume, 3-7 nerved, hairy.

On stalked spikelet, outer glume, 4 times as long as wide, 7 ribbed with a pointed tip.

Palea - Hairy.

Lemma - On stalkless spikelet. Translucent with a bent awn about 7-32 mm long arising from the notch or awnless. Hairy. Lower lemma 2 nerved, upper lemma 1 nerved.

Stamens - Often in stalked spikelets.

Anthers -


Red brown to black, 3-4 mm long, egg shaped. Surface finely lined.


Creeping, rooting, scaly, branched, underground, purple spotted, rhizome to 300 mm deep. Fibrous roots extend up to 1200 mm deep and 1000 mm diameter.

Key Characters:

Rhizomatous perennial.

Pubescent lower nodes.

Culms arising from elongated rhizomes.

Racemes not in pairs, supported by a common spathe.

Inflorescence a panicle, not enclosed in the leaf sheath, comprising both bisexual and male or sterile spikelets.

Bisexual floret single.

Spikelets several, usually in pairs at least towards the base of the raceme.

Glumes of fertile spikelets not keeled, lacking pits, the 1st becoming smooth and shining.

Lemmas 2 or more, awned, 1st lemma sterile or male.

From J.M. Black and N.T. Burbidge.


Life cycle:

Perennial. Flowers November to June. Seeds germinate in spring to early summer. Initially top growth is slow as roots and rhizome develops. Flowering commences about 7 weeks after germination. After flowering rhizome grows quickly. Flowering is continuous over the summer with a peak in early and late summer. Rhizomes dormant over winter. Top growth dies after frosts in winter. New shoots emerge from rhizomes in spring. Shots from rhizomes emerge earlier and grow faster than those from seed. Rhizomes are short-lived and are produced in one season, sprout in the next season to form a new plant then die as new rhizomes are formed.


Rhizomes are drought tolerant and store starch.

It is a C4, tetraploid (2n=40) plant.

Maximum growth occurs at 30-40% full sunlight, 16 hour day lengths and 20-300C.

Growth rate starts to fall around 20% full sunlight.

Optimum temperature for rhizome and shoot growth is about 300C.

Rhizome only sprout at high temperatures with an optimum around 300C.

Rhizome buds are killed 2-3 days exposure to soil surface temperatures of 50-600C or -30C.

Rhizome and panicle formation are delayed in dense infestations. Most of the reproductive effort is devoted to rhizome production.


By seed and rhizomes and rhizome fragments.

Flowering times:

Summer to autumn in western NSW.

November to May in SA.

November to June in Perth.

Late spring to early winter in WA.

Seed Biology and Germination:

Fresh seed won't germinate for a few months after harvest. After this, 20-40% of seed is hard or dormant and won't germinate for some years. In the soil, it may remains viable for more than 10 years and has a half life of just over 2 years. Dormancy is due to the persistent glumes and seed coat and if these are removed nearly all seed germinates including freshly harvested seed.

Germination is generally higher on sands than clays.

Seed will not germinate if the temperature is less than 150C.

Germination is greatest in light, alternating temperature, high nitrate and moist conditions.

Vernalisation(exposure to cold followed by hot conditions) increases germination.

Germination declines as depth increases beyond 25 mm deep with few emerging from more than 160 mm deep.

There is considerable variation in germination characteristics between the varieties.

Vegetative Propagules:

Rhizome and rhizome fragments sprout readily in hot conditions.


Forms many hybrids.

Columbus grass (Sorghum X almum) are the fertile hybrids between Johnson Grass (Sorghum halepense) and cultivated Sorghum (Sorghum bicolor) and some are these are useful fodders.


Release of toxins that retard surrounding plants

Population Dynamics and Dispersal:

Seed is spread by wind, water, animals and in produce. It passes in the dung of birds and stock. Rhizomes may be spread by earth moving equipment.

A 60 mm rhizome fragment can increase to nearly 600 mm and produce 100 buds in a year. Long fragments have a greater chance of survival than short fragments.

Origin and History:

Tropical areas. North Africa. Mediterranean. South west Asia.

Probably introduced as a forage grass around 1850.

In Adelaide in 1871, naturalised in NSW by 1883




Irrigation areas. Summer moist areas.


Tropical, sub-tropical and temperate areas.


Moist soils.

Plant Associations:


It is listed as one of the 10 worst weeds in the world.


Palatable fodder.

Ornamental garden plant.


Weed of crops, rotation crops, perennial crops, grass land, pastures, roadsides, irrigated areas, swamps and disturbed areas.

Aggressive weed causing severe crop losses due to competition and allelopathy.

Alternate host for pests such as sorghum midge and diseases such as sugar cane mosaic virus, which causes dwarf mosaic disease in sorghum and maize.

Crosses with sorghum producing weedy biotypes.


Toxic when stressed, frosted, wilted or stunted. Produces HCN and causes cyanide poisoning. Young shoots are probably the most toxic.

Cattle, sheep and pigs have been poisoned in Australia. Cattle appear to suffer the worst losses.

It may also contain toxic levels of nitrate and cause nitrate poisoning especially during periods of vigorous growth.


Death is usually rapid and few symptoms reported apart from blue skin and mucous membranes.


HCN poisoning.


Noxious weed of NSW and NT.

Management and Control:

Cultivation every 3-4 weeks to exhaust rhizomes is effective.

Mowing regularly is also effective if a low growing perennial is present to replace the Johnson grass.

Mulching with black or clear plastic is used in horticultural situations. Black plastic covered with soil has been used in vineyards. Clear plastic placed on top of moist cultivated soil for 30-50 days increases soil temperature and often provides control of Johnson Grass and other weeds and diseases.

A number of herbicides provide good control of Johnson grass in various crops and situations.

Best results are usually obtained with integrated programs. Rhodes Grass and Couch Grass has been a useful competitor plant because their tolerance to MSMA used to suppress Johnson Grass. MSMA is best applied at early flowering on warm (>250C) days. Crop and pasture rotations that include, cultivation, grazing and herbicides often keep Johnson Grass at low levels.

In non arable areas, burning or slashing in December and applying herbicides in February provides good control. The herbicide chosen should have the least effect on competitive companion species. In non selective situations glyphosate is usually the most cost effective.


Low levels should be controlled to prevent build up in successive crops.

Eradication strategies:

Difficult to eradicate because seed lasts in the soil for many years and rhizomes readily sprout when damaged.

Prevent seed set and control rhizomes

Herbicide resistance:

Tolerant to triazine herbicides.

Biological Control:

Several biocontrol agents have potential but require careful testing because Johnson grass is closely related to important agricultural and native species.

Related plants:

Annual Native Sorghum (Sorghum stipoideum)

Broom Millet (Sorghum dochna)

Brown Sorghum (Sorghum nitidum)

Columbus grass (Sorghum X almum) are the fertile hybrids between Johnson Grass (Sorghum halepense) and cultivated Sorghum (Sorghum bicolor) and some are these are useful fodders such as Columbus grass.

Downs Sorghum (Sorghum timorense, Sorghum australiense)

Forage Sorghum (Sorghum bicolor)

Plume Sorghum (Sorghum plumosum)

Sudan grass (Sorghum sudanense)

Wild Sorghum (Sorghum arundinaceum, Sorghum leiocladum, Sorghum arundinaceum, Sorghum verticilliflorum)

Sorghum interjectum

Sorghum macrospermum.

Plants of similar appearance:



Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P58. Photos.

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P248. Diagrams.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P72.

Ciba Geigy (1980) Grass Weeds 1. CIBA GEIGY Ltd, Basle, Switzerland. P136. Diagrams.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P139-140. Photo.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P348. plate 23-24.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P70. Photo.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #1147.6.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P989.

McBarron, E.J. (1983). Poisonous plants. (Inkata Press, Melbourne). P20. Diagram.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P125-130.

Paterson, J.G. (1977). Grasses in South Western Australia. (Western Australian Department of Agriculture Bulletin 4007). P86. Diagram.


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