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Water dropwort (Oenanthe pimpinelloides)

Water Dropwort is an invasive perennial herb and an agricultural sleeper weed with potential to spread in southern temperate Australia. It can replace pasture species and compete with native plants, and it has been reported to be poisonous in large quantities.

Key facts

Type: Weed, herb.

Native to: Western Europe and the Mediterranean region, from Morocco to the Middle East.

Established in: VIC, SA.

Other names: Meadow Parsley, Corky Fruit, Corky-fruited Water Dropwort.

Best time to act: Look for plants as rosettes in spring; herbicide treatments at stem elongation in spring, before autumn pasture sowing, are reported to provide effective short-term control, and flowering occurs from October to December.

Identification

  • An erect perennial herb, usually 30 to 100 cm tall, it produces basal rosettes in spring and a solid, striated, branching stem.
  • Its leaves are parsley-like or fennel-like, with divided basal leaves and narrower stem leaves.
  • Small white flowers form umbrella-shaped clusters at the ends of stems, 20 to 50 mm across.
  • The cylindrical fruit is about 3 mm long, strongly ribbed and may look spiny at the tip.
  • Roots have rounded tubers towards their ends.
  • Look-alike: It can resemble other parsley- or fennel-like plants in the carrot family; take extreme care not to confuse it with poisonous Cowbane (Cicuta virosa), Hemlock (Conium maculatum) or Hemlock Water Dropwort (Oenanthe crocata).
  • Look-alike: It may be confused with Yarrow (Achillea millefolium), which has large, feathery leaves.

Where it grows

In Australia it is recorded in South Australia around Meadows in the Mount Lofty Ranges, in Victoria at Shepparton State Forest and near Wonthaggi, and in northern Tasmania near the Meander River, in moist seasonal meadows, pastures, wetlands, watercourses and roadsides.

Why it matters

  • It can replace pasture species and compete with native species, particularly during summer.
  • Crops, grazing land and horticulture are among the land uses potentially at risk from its spread in southern temperate Australia.
  • It could affect natural ecosystems by out-competing native plants.

How it spreads

  • Seed is its primary means of spread; seeds can float away on water and may also be spread by wind, stock, hay and machinery.
  • Root tubers also spread vegetatively, including along watercourses and as contaminants of hay.

Control options

  • Eradication has been recommended for this Category 2 sleeper weed; larger infestations may need an integrated approach using registered herbicides where appropriate and establishing competitive species.
  • Smaller infestations can be removed by hand.
  • Maintain dense pasture: perennial grasses such as Phalaris and broad-leaved species such as white or subterranean clover can reduce seedling survival.
  • Take care around waterways and wetlands when using herbicides, and always follow the product label.

Hygiene and washdown

  • Check and clean machinery to reduce the risk of spreading seeds.
  • Avoid moving infested hay, which can carry seeds and root tubers.
  • 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: 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: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • 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.

  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board

Sources