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Stinkwort (Dittrichia graveolens)

Stinkwort is a widespread weed of southern Australia, affecting agricultural land and disturbed areas, and can invade some native vegetation. Its strongly scented oil can cause allergic contact dermatitis, and the plant is generally unpalatable to grazing animals.

Key facts

Type: Weed, herb.

Native to: Mediterranean region.

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

Other names: Stinkweed, Stink-weed, Camphor Inula, Khaki Weed.

Best time to act: Look for seedlings and rosettes after spring germination and treat plants while young, before flowering, which occurs mainly from March to May.

Identification

  • It is an erect, sticky, much-branched annual herb, usually 30–60 cm tall but able to grow to 1.2 m.
  • Leaves and stems have hairs and small glands that exude sticky, strongly scented oil with a camphor or kerosene-like smell.
  • The narrow stem leaves are smaller than the first leaves, which form a basal rosette.
  • Small yellow, daisy-like flower heads grow singly along leafy branches, mainly from March to May.
  • After flowering, the heads produce hairy, one-seeded fruits crowned with fine, feathery hairs.
  • Look-alike: It can resemble Aster-weed (Aster subulatus) and fleabanes (Conyza spp.), but Stinkwort’s strongly scented, glandular leaves, stems and flowering branches help distinguish it.

Where it grows

In Australia it is widespread in New South Wales, Victoria, South Australia, Tasmania and southwest Western Australia, with limited patches in the Australian Capital Territory and southeast Queensland and a single Northern Territory collection, and it grows in open disturbed sites such as roadsides, pastures, vacant lots and waterways.

Why it matters

  • It is an agricultural weed of pastures, crops, lucerne, fallows, roadsides, railways and irrigated or disturbed areas, and is also regarded as an environmental weed in some places.
  • Its oil can cause allergic contact dermatitis in some people.
  • Grazing animals generally find it unpalatable and eat it mainly when young and little else is available; the oil can taint meat and milk, and discolour wool.
  • It is considered a potential threat to dry coastal vegetation, mallee shrubland, lowland grassland, grassy woodland and dry sclerophyll forest and woodland.

How it spreads

  • Stinkwort spreads by seed only, and its seeds can survive in the soil seedbank for up to three years.
  • The fruit’s feathery hairs aid dispersal by wind and water, and fruits can also travel on machinery, vehicles, wool, skins, bags and clothing.
  • Fruits can be spread in sand and gravel used for road making.

Control options

  • Treat young plants in the rosette stage before flowering; older plants are relatively tolerant of herbicides, and plants sprayed in flower may set seed and regrow.
  • Use registered herbicides according to current directions, or hand-pull isolated plants and small patches before flowering, wearing gloves.
  • Cultivate or slash large areas before flowering, then follow up regrowth; cut plants in bud or flower can still produce viable seed and should be bagged and dumped or heaped and burned.
  • Heavy grazing by sheep when plants are young can help, and autumn or winter super-phosphate application can promote pasture growth that competes with Stinkwort.

Hygiene and washdown

  • Seed-bearing fruits can be carried on machinery, vehicles, wool, skins, bags and clothing; contaminated sand and gravel used for road making are also a pathway.
  • 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 controlled / restricted weed (varies by region). 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: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Permitted, not declared. Listed as a permitted organism in WA, so it can be brought in, but it is not a declared pest.
  • 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.

  • 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