Johnson grass (Sorghum halepense)

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Johnson grass is a clumping perennial grass up to 2 m tall. It invades cropping land and is a host of crop pests and diseases.

This plant should not be sold in parts of NSW

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How does this weed affect you?

Johnson grass:

competes with crops, reducing yields, including sugarcane and soybeans
is a host of crop pests and diseases
can contaminate seed crops including grain sorghum
is poisonous to livestock (contains cyanogenetic glycoside and high levels of nitrates).

What does it look like?

Johnson's grass is an erect perennial grass up to 2m tall.

The leaves have a pronounced mid-vein and rough margins. They are 2–50 cm long and 0.5–2 cm wide.

The seedhead is 10–35 cm long, green to purplish, with loose spreading branches.

Where is it found?

In NSW, Johnson's grass is widely distributed across NSW except for in the Western region.

It originates from the Mediterranean region.

Johnson grass grows in tropical, subtropical and temperate climates. It is common in wet areas such as irrigated paddocks and crops, along waterways and roadsides.

Maps and records

Recorded presence of Johnson grass during property inspections (Map: Biosecurity Information System - Weeds, 2017-2026)
These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.

How does it spread?

Johnson grass produces seeds which are spread by wind, water, sticking to wool and fur and in contaminated produce. Seeds can also spread stuck in mud attached to vehicles or machinery.

Plants can grow from rhizomes, which are spread by cultivation and roadside grading.

References

Parsons, W.T., & Cuthbertson, E. G. (2001). Noxious weeds of Australia. 2^nd edition. CSIRO publishing.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved from https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Sorghum~halepense

More information

Control

Pasture management

Maintain strong, competitive pastures to prevent new infestations.

Slashing and mowing

Repeated, slashing or mowing can prevent seeding, reduce growth rates and allow other species to compete with the Johnson grass. .

By hand

For small infestations, dig out individual plants when the soil is moist and roots are less likely to break.

Herbicide control

Spray actively growing plants. Seedlings and young plants are very susceptible to herbicide treatments applied before seedheads appear. Check labels for the best spraying times.

Cover all of the foliage with the herbicide mixture.

Herbicide options

WARNING - ALWAYS READ THE LABEL
Users of agricultural or veterinary chemical products must always read the label and any permit, before using the product, and strictly comply with the directions on the label and the conditions of any permit. Users are not absolved from compliance with the directions on the label or the conditions of the permit by reason of any statement made or not made in this information. To view permits or product labels go to the Australian Pesticides and Veterinary Medicines Authority website www.apvma.gov.au

See Using herbicides for more information.

Flupropanate 745 g/L (Various products)
Rate: 200 mL per 15 L of water
Comments: Knapsack spray when plants are actively growing and not less than 30 cm high. Spray thoroughly to the point of run-off.
Withholding period: Spot spray: Do NOT graze or cut for stock feed for at least 14 days. Blanket spray: Do NOT graze, or cut for stock feed for at least 4 months. If stock are grazed in treated areas after required time has passed, remove stock from treated areas and do NOT slaughter or milk for human consumption until they have been on clean feed for at least 14 days.
Herbicide group: 15 (previously group J), Inhibition of very long chain fatty acid synthesis (VLCFA inhibitors)
Resistance risk: Moderate

Flupropanate 745 g/L (Various products)
Rate: 1.0 L per 100 L of water
Comments: High volume spot spray when plants are actively growing and not less than 30 cm high. Spray thoroughly to the point of run-off.
Withholding period: Spot spray: Do NOT graze or cut for stock feed for at least 14 days. Blanket spray: Do NOT graze, or cut for stock feed for at least 4 months. If stock are grazed in treated areas after required time has passed, remove stock from treated areas and do NOT slaughter or milk for human consumption until they have been on clean feed for at least 14 days.
Herbicide group: 15 (previously group J), Inhibition of very long chain fatty acid synthesis (VLCFA inhibitors)
Resistance risk: Moderate

Glyphosate 360 g/L (Various products)
Rate: 1.0 L per 100 L of water
Comments: Spot spray with a handgun. Apply to actively growing plants at the early head stage.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

Glyphosate 360 g/L (Various products)
Rate: 6.0 L/ha
Comments: Boom spray actively growing plants at early head stage.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

Glyphosate 360 g/L (Various products)
Rate: 1.0 L glyphosate per 2 L of water
Comments: Wiper equipment a minimum of 10 cm above the crop or pasture. Weeds should be at least 15 cm above the crop or pasture. Speed of travel 8 km/h or less. Best results are achieved at lower speeds and where two applications are made in opposite directions.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

Imazapyr 750 g/kg (Various products)
Rate: 2 kg/ha
Comments: Boom spray application of soluble granule herbicide for pre- and post-emergent control.
Withholding period: Do not graze or cut for stock food for 8 weeks after application.
Herbicide group: 2 (previously group B), Inhibition of acetolactate and/or acetohydroxyacid synthase (ALS, AHAS inhibitors)
Resistance risk: High

Biosecurity duty

The content provided here is for information purposes only and is taken from the NSW Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area	Duty
All of NSW	General Biosecurity Duty All pest plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
Central West	Regional Recommended Measure * (for Regional Priority - Asset Protection) Land managers should mitigate the risk of the plant being introduced to their land. Land managers should mitigate spread of the plant from their land. A person should not buy, sell, move, carry or release the plant into the environment. Land managers should reduce the impact of the plant on assets of high economic, environmental and/or social value.
	*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

For technical advice and assistance with identification please contact your local council weeds officer.

Reviewed 2025