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Hoary cress (Lepidium draba)

Hoary Cress is a major weed of cropping across much of temperate Australia and can seriously reduce crop yields. Its persistent root system makes established infestations difficult to eradicate, and cultivation can spread it.

Key facts

Type: Weed, herb.

Native to: Eastern Mediterranean through Asia Minor to southern and central Asia.

Established in: QLD, NSW, ACT, VIC, TAS, SA, WA.

Other names: White Weed, Hoary Pepperwort.

Best time to act: It is easiest to identify when flowering from September to November; herbicide timing is critical and treatments may be needed over several years.

Identification

  • It is a perennial herb, usually erect or sometimes flat to erect, growing 150 to 900 mm tall.
  • Stems and leaves are densely covered in soft, minute hairs, giving the plant a greyish or bluish green colour.
  • White flowers form numerous dense, flat-topped clusters, with hundreds of flowers in a cluster.
  • Its inflated, heart-shaped fruits are about 3 to 5 mm long and contain one or two seeds in each of two chambers.
  • Look-alike: Shepherd's Purse is an annual and almost hairless, with triangular or nearly heart-shaped fruits.
  • Look-alike: Penny Cress is an uncommon annual weed with no hairs and larger, rounded fruits, about 10 to 20 mm long.

Where it grows

In Australia it occurs in cereal-growing areas, vegetable-growing areas, roadsides, waste places, drainage lines and irrigation ditches, and favours alkaline soils.

Why it matters

  • It competes with grain crops, pastures and horticultural crops, causing serious yield reductions and sometimes interfering with harvesting.
  • It is highly competitive, and chemicals in its roots hinder the germination and growth of companion plants, especially cereals.
  • Infestations can dominate fields and are very difficult to eradicate because of the vigorous perennial root system.
  • It is seldom grazed, but milk and meat may become tainted if stock consume it for about a week; it is also suspected of causing stock losses.

How it spreads

  • It spreads mainly through lateral roots and broken root fragments, which can rapidly produce new plants after cultivation.
  • Seeds are spread in contaminated soil, hay, grain, vehicles and equipment, and can also move with water.
  • Roadside maintenance and contaminated agricultural produce can also disperse seeds and roots.

Control options

  • Registered herbicides can be used, but application timing is critical and several years of treatment may be required.
  • Cultivation alone is not sufficient for long-term control; intensive cultivation at monthly or fortnightly intervals over several years has been described, with follow-up normally required.
  • Avoid single cultivation, combine control techniques and establish competitive species or use longer pasture phases in cropping rotations.
  • Time grazing to prevent seed production, and restrict movement of stock that have grazed mature plants.

Hygiene and washdown

  • Clean cultivation, harvesting and road-maintenance machinery after work in infested areas, as root fragments and contaminated soil can spread the weed.
  • Use hay and crop seed sourced from uninfested paddocks, because these can carry Hoary Cress seed.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Not a priority weed. Not a state or regional priority weed in NSW. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Regionally prohibited / regionally controlled / restricted weed (varies by region). Where it is regionally prohibited, landowners must take all reasonable steps to eradicate it on their land. Where it is regionally controlled, landowners must take all reasonable steps to prevent its growth and spread on their land. Where it is a restricted weed, trade in it (including the plant, its seed or contaminated material) is prohibited.
  • South Australia: Declared plant. Depending on the declaration, it can be an offence to move it on public roads or sell it, and landowners may be required to control it on their land.
  • Western Australia: Declared pest (C2), prohibited. C2 Eradication: present in limited areas and targeted for eradication. It must not be brought into WA (prohibited organism).
  • Tasmania: Declared weed. Property managers are required by law to control declared weeds, and their import and sale are prohibited.
  • Northern Territory: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Queensland: Biosecurity Act 2014 (Qld), administered by Biosecurity Queensland (13 25 23)
  • New South Wales: Biosecurity Act 2015 (NSW), administered by NSW Department of Primary Industries and Regional Development
  • Australian Capital Territory: Biosecurity Act 2023 (ACT), administered by ACT Biosecurity
  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • Tasmania: Biosecurity Act 2019 (Tas), administered by Biosecurity Tasmania
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board
  • Western Australia: Biosecurity and Agriculture Management Act 2007 (WA), administered by the WA Department of Primary Industries and Regional Development

Sources