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Red witchweed (Striga asiatica)

Red witchweed is an introduced parasitic plant that can severely damage or destroy important crops. It was found on sugarcane properties near Mackay, Queensland, in 2013 and is a target of a national eradication program.

Key facts

Type: Weed, herb.

Native to: Tropical Africa and parts of Asia.

Established in: .

Other names: Asiatic witchweed.

Best time to act: Inspect closely during warm conditions and report plants as soon as they emerge, since they can remain hidden underground for four to seven weeks and produce seed rapidly after emergence.

Identification

  • It is an annual parasitic herb that grows close to host plants and may stay hidden underground for four to seven weeks before emerging.
  • Plants are usually 15 to 20 cm tall, though some can reach 60 cm; stems are white and round underground, and four-sided with short, hard hairs above ground.
  • The narrow green leaves are 6 to 40 mm long and 1 to 4 mm wide.
  • Small red flowers, 5 to 8 mm wide, grow near the top of the stem beside a leaf and have four or five petals.
  • The capsules mature from green to brown and contain many dust-like seeds; a plant can produce at least 50,000.
  • Look-alike: Other witchweeds, including the native Striga parviflora, may be difficult to distinguish; seek expert identification.

Where it grows

In Australia it can grow in intensive crop monocultures, especially where host crops such as sugarcane, maize, millet, rice, sorghum or legumes are present, and may also grow in grasslands, pastures or bushland.

Why it matters

  • It parasitises host-plant roots and takes nutrients, stunting or killing the host.
  • It can completely destroy crops including maize, millet, rice, sugarcane, sorghum and legumes.
  • Infested plants can show wilting and shrivelling despite moist soil, with symptoms resembling drought stress, nutrient deficiency or disease.
  • It is difficult to control and may not be noticed until the crop is already seriously affected.

How it spreads

  • Tiny sticky seeds can remain viable in soil for over 10 years and can be moved in contaminated soil on machinery, tools, footwear and clothing.
  • Seeds can also spread in contaminated crop seed or livestock feed, in livestock manure or on animal coats, and by wind or water.

Control options

  • Do not touch, treat or dispose of suspected plants yourself; report them immediately to the relevant state biosecurity agency. In NSW, call the Biosecurity Helpline on 1800 680 244.
  • In NSW, DPIRD leads the initial treatment and disposal response; follow biosecurity officers' directions and do not move affected plant material.
  • Arrange follow-up surveillance and any further treatment through biosecurity officers, because seeds can persist in soil for over 10 years.

Hygiene and washdown

  • Avoid moving soil or plant material from a suspected infestation, and clean machinery, tools, footwear and clothing before moving between sites.
  • Do not move potentially contaminated crop seed or livestock feed, and take care to prevent livestock spreading seeds in manure or on their coats.
  • 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): National weed eradication program. Targeted for eradication under the nationally cost-shared Red Witchweed National Eradication Program. Report any sighting straight away.
  • Queensland: Prohibited matter. Report it to Biosecurity Queensland on 13 25 23 within 24 hours and do not move or deal with it. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Prohibited matter. It is an offence to deal with it, and you must notify NSW DPIRD as soon as you become aware of it.
  • 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: 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: Declared weed. Property managers are required by law to control declared weeds, and their import and sale are prohibited.
  • Northern Territory: Declared weed. Weeds Australia lists it as a declared weed in the NT under the Weeds Management Act 2001. Check the NT declared weeds list for its class and what it requires.
  • 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