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Penny cress (Thlaspi arvense)

Penny Cress is uncommon in Australia and has been recorded only on a handful of occasions, but it is a declared weed in Western Australia. Its leaves and seeds can be toxic to livestock.

Key facts

Type: Weed, herb.

Native to: Temperate and tropical Asia, Macaronesia and Europe..

Established in: .

Other names: Frenchweed, Fanweed, Field Pennycress, Stinkweed.

Best time to act: Look for flowering plants from late spring through summer and early autumn in Australia; the species can also germinate in winter crops.

Identification

  • It is a hairless, erect annual herb, occasionally biennial, growing up to 60 cm tall.
  • Lower leaves are oblong to lance-shaped, slightly toothed and up to 5 cm long; upper leaves get smaller and clasp the stem.
  • The flowers have four small white petals, up to 4 mm long.
  • The strongly flattened, nearly circular fruits are 12–22 mm across, with two broad, thin wings and a deep notch at the end.
  • Each fruit contains several small purplish-brown seeds when ripe, and the crushed plant has an unpleasant odour.
  • Look-alike: Some native and exotic Lepidium species may be mistaken for Penny Cress, but their fruits are smaller, up to 9 mm wide, and contain only two seeds.
  • Look-alike: Shepherd's Purse has triangular or almost heart-shaped fruits; Hoary Cress is densely covered in fine soft hairs and has inflated, upside-down pear-shaped fruits.

Where it grows

In Australia it occurs in south-east Queensland, on the Northern Slopes and Tablelands of New South Wales, and at Pawtella in Tasmania; it has also been recorded at Leongatha South in Victoria, where it is now believed to be absent.

Why it matters

  • It is a serious weed of crops, gardens, pastures, disturbed sites and waste areas in temperate and subtropical regions of the world.
  • In North America it is an important weed of grain, oilseed and forage crops.
  • Its seeds and leaves can be toxic to livestock, and can taint milk and meat with unpleasant flavours when present in hay or other fodder.
  • Poisoning, death and abortion have occurred in cattle in western Canada after they ingested hay containing high quantities of Penny Cress.

How it spreads

  • Penny Cress reproduces by seed and Canadian studies report up to 15,000 seeds per plant.
  • Its thick seed coat enhances dormancy, and seeds can remain viable for up to 20 years.
  • Seeds are most often spread as a contaminant of agricultural produce.

Control options

  • Herbicides can provide effective control.
  • Use registered herbicides and consult the Australian Pesticides and Veterinary Medicines Authority for chemical information.
  • Plants resistant to Group B/2 herbicides have been found in Canada.

Hygiene and washdown

  • Because seeds are most often spread as contaminants of agricultural produce, check produce for contamination before moving it.
  • 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: Not declared. Not declared under the Catchment and Land Protection Act 1994. Other Victorian laws may still apply.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Declared pest (C1), prohibited. C1 Exclusion: to be kept out of WA, or out of the parts of WA where it is not established. Report any sighting to DPIRD. It must not be brought into WA (prohibited organism).
  • Tasmania: Not declared. Not a declared weed in Tasmania. Other laws may still apply.
  • 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.

Sources