Hoary cress (Lepidium draba)

Also known as: white weed

Hoary cress is a deep-rooted perennial herb. It is a major crop weed and is widespread throughout most of temperate Australia’s cropping regions.

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How does this weed affect you?

Hoary cress is an invasive plant of pastures, cereal crops, horticultural crops, roadsides and neglected areas. In cropping systems, hoary cress can significantly reduce crop yields, interfere with harvesting and is a grain contaminant. As it is part of the Brassica family, it poses a major problem when canola is part of the cropping rotation, as it cannot be controlled in-crop. In grazing situations, it can taint the meat and milk of animals that eat it.

Where is it found?

A native to the eastern Mediterranean, through to central and southern Asia. Hoary cress is a weed in Europe, the Middle East, South Africa, New Zealand and the USA.

Thought to have entered the country as a grain contaminant. It is now present at various locations and densities throughout the cropping areas of New South Wales, Victoria, South Australia, Tasmania, southeast Queensland and southern Western Australia. 

How does it spread?

Hoary cress can reproduce by seed, although most new plants arise from its spreading roots and broken root segments. The well developed lateral roots produce new shoots from buds that occur along its length. Cultivation is a common cause of root spread. Thousands of seeds are produced per year by each plant, with around 80% viability. Seeds can be spread by contaminated soil, hay, grain, vehicles and equipment.

Lifecycle

Seeds germinate in autumn. New growth from root buds will also occur in autumn. Seedlings grow and develop during the winter and spring.  Flowering stems begin to emerge from early spring, with flower heads developing through to late spring. It is uncommon for plants that have germinated from seed to flower in their first year.  Instead they use their energy to develop a deep and extensive root system.  Stems die back in summer after flowering and remain dormant until autumn. 

What does it look like?

Hoary cress is an erect perennial herb capable of growing to 90 cm tall, but more commonly reaches heights of 75 cm.

Stems

• upright
• branched near the top
• covered in fine hairs
• has ribs that run the length of the stem

Leaves

• covered in soft, fine hairs
• greyish green or bluish green in colour
• occur alternately along the stem
• variable shape from oblong to wedge-shaped
• lower leaves occur on short stalks, are long and narrow (up to 10 cm long) with toothed edges
• the base of upper leaves clasp the stem

Flower

• white, 4–6 mm in diameter
• 4 small petals, up to 4 mm long
• occur at the end of branches in dense flat-topped clusters
• fragrant

Fruit

• heart-shaped capsule
• 2–4 mm long and 3–5 mm wide
• separates into 2 parts when mature
• contains 1–2 seeds
• mature fruit has a network of veins on surface

Seed

• reddish-brown in colour
• about 2 mm long
• oval

Roots

• woody taproot reaches to about 2 m deep
• branched lateral root system, producing shoots at irregular intervals

What type of environment does it grow in?

Hoary cress prefers warm, temperate conditions with an annual rainfall over 400 mm.  It can grow in a variety of soil types, but prefers alkaline loams. It will thrive in loose, rich soils that allow rapid lateral root growth.

References

Department of the Environment (2011) Weeds in Australia: Lepidium draba. Australian Government. Available at: http://www.environment.gov.au/biodiversity/invasive/weeds/identification/index.html 

Hosking JR, Sainty GR, Jacobs SWL & Dellow JJ (in prep) The Australian WeedBOOK.

Lamp C and Collet F (2004) Field guide to weeds in Australia, Inkata Press, Melbourne.

Parsons, WT and Cuthbertson, EG (2001) Noxious weeds of Australia, CSIRO Publishing, Collingwood.

More information

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Control

To control hoary cress, property hygiene practices should be in place to restrict movement of roots and seed into clean areas.

Avoid using cultivation as broken root pieces can increase infestations or spread the weed to new locations.

Herbicides

Herbicides should preferably be applied when the plant is in its rosette form, is actively growing and before flowering. This is usually from winter to autumn.

Herbicide can be applied as a spot spray or boom spray application, depending on the herbicide chosen.

Follow up treatments will be required.

Herbicide options

See Using herbicides for more information.

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2,4-D amine 625 g/L (Various products)
Rate: 1.1–1.7 L/ha
Comments: Boom spray application, at rosettes to pre-flowering.
Withholding period: 7 days withholding for grazing
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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2,4-D LV ester 680g/L (Estercide® Xtra)
Rate: 1.7 to 2.1 L/ha
Comments: Boom spray application, from late rosette to pre-flowering
Withholding period: Do not graze or cut for stock food for 7 days after application.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

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Glyphosate 360 g/L (Various products)
Rate: 500 mL per 100 L of water
Comments: Spray actively growing plants with a handgun. For maximum long term reduction, apply from late July to September when plants are in late rosette to flowering stage.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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Glyphosate 360 g/L (Various products)
Rate: 1.5 L/ha
Comments: Boom spray actively growing plants. For maximum long term reduction, apply from late July to September when plants are in late rosette to flowering stage.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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Glyphosate 360 g/L (Various products)
Rate: 75 mL per 15 L of water
Comments: Spray actively growing plants with a knapsack. For maximum long term reduction, apply from late July to September when plants are in late rosette to flowering stage.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

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Biosecurity duty

The content provided here is for information purposes only and is taken from the 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.

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Reviewed 2024