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Calomba daisy (Oncosiphon suffruticosus)

Calomba daisy can dominate perennial pastures, competing with more valuable pasture plants and reducing the area available for grazing. It can also reduce cereal crop yields, and stock may taint meat and milk if they eat the unpalatable plant when other feed is scarce.

Key facts

Type: Weed, herb.

Native to: Cape Province, South Africa, and Namibia.

Established in: SA, WA.

Other names: Shrubby mayweed, Chamomile, Mayweed, Stinking daisy.

Best time to act: Look for seedlings in autumn and rosettes over winter, and hoe young plants before flowering, which occurs from September to December.

Identification

  • An upright, dense, spreading, aromatic annual herb, usually 200 to 600 mm tall but sometimes reaching 1 metre.
  • Its stout stems become woody with age and are usually unbranched below the flower heads.
  • Grey-green leaves are deeply divided into thin lobes, covered with short soft hairs, and clasp the stem.
  • Numerous small, yellow flower heads, about 3 to 5 mm across, form dense, flat-topped clusters at the ends of stems.
  • Its wedge-shaped, grey-brown fruits are about 1 to 1.5 mm long and have a small crown of white scales.
  • Look-alike: Globe chamomile (Oncosiphon piluliferum) is shorter, has shorter leaves and larger flower heads, and bears fewer flower heads per stem; its heads are globose, while Calomba daisy's are more club-shaped.
  • Look-alike: Matricaria species have ovoid flower heads and are hairless, unlike Calomba daisy, which has subglobose flower heads and hairs on the plant.

Where it grows

In Australia it is found mainly in semi-arid parts of Western Australia and South Australia, in disturbed areas such as pastures, cultivated fields, roadsides and waste areas.

Why it matters

  • It can invade and dominate perennial pastures, competing with more valuable pasture plants for water, light and nutrients and reducing grazing area.
  • It is aromatic, unpalatable to stock and has no food value; if eaten when other feed is scarce, it can taint meat and milk products.
  • It can invade crops and significantly reduce cereal yields, particularly if it germinates late in a stressed or uncompetitive crop.

How it spreads

  • Seeds tend to remain in the flower head until it breaks up; whole flower heads can be moved by wind, animals or vehicles.
  • Seeds may also be carried in fodder and produce, and in gravel and soil.
  • Most seeds germinate the following autumn, but a small proportion can remain dormant for three years or longer.

Control options

  • Use registered herbicides appropriate to the site; some populations in South Australia have evolved herbicide resistance.
  • Spot spraying is described as the most cost-effective option for small or isolated patches, and larger infestations can be treated with herbicides selected to avoid damage to crops and pasture.
  • Hoe small infestations and outlying plants while they are young.
  • Maintain good pasture cover and appropriate stocking density, and remove small patches; slashing, mowing and grazing rarely control the weed, which can regenerate after rain.

Hygiene and washdown

  • Clean vehicles and equipment after working in infested areas, as seeds can be moved by vehicles and in gravel or soil.
  • Avoid moving contaminated fodder or produce, which may carry seeds.
  • 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: 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.

  • 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