Red witchweed (Striga asiatica) is a parasitic plant that grows attached to the roots of certain commercially important grasses and summer cereals, including sorghum, corn (maize), rice and sugarcane. It has the potential to reduce crop yields by up to 70%.
Red witchweed (Striga asiatica) was first detected on a sugar cane property in Mackay on 11 July 2013. Extensive surveillance following this detection identified a total of eight infested properties.
The Queensland government has undertaken response activities since red witchweed was first detected, including treatment, surveillance, on-farm biosecurity restrictions and research activities.
In July 2015 the National Management Group (NMG) agreed on a ten year national response plan to eradicate red witchweed. The response plan was endorsed by the Agriculture Ministers’ Forum (AGMIN) in April 2016, with continuation beyond the intensive three year treatment period subject to an independent efficacy review.
In August 2017, the Red Witchweed Consultative Committee endorsed the continuation of the treatment phase until 30 June 2019. This proposal was endorsed by the NMG in July 2019.
After four years of treatment there has been a 99% reduction in the number of red witchweed detections and a demonstrated 85% decline in the soil seedbank.
An independent efficacy review of the response program was completed in April 2019. The review panel made several recommendations and concluded that eradication remains technically feasible, subject to an extension of the treatment period and increased resourcing.
On 12 December 2019 the Red Witchweed Consultative Committee met to discuss the progress of the Red Witchweed Eradication Program and endorsed a revised response plan, subject to minor amendments. This plan was approved by NMG on 5 June 2020 and allows for response activities to continue until June 2025, with the provision of a cost-shared budget of $5.25 million.
About red witchweed
A number of Australia’s trading partners consider red witchweed a quarantine pest for a range of our seed and grain exports, with conditions in place to address the risk of red witchweed contamination.
Red witchweed is a parasitic plant that grows attached to the roots of suitable hosts then survives by taking the host plant’s nutrients and water. Symptoms of red witchweed infestation include stunting, wilting and chlorosis of the host plants.
Host plants include sugarcane, sorghum, maize and rice. Research has identified wheat and barley are potential hosts. Red witchweed can survive in a range of soils but generally prefers sandy or gravelly soils in tropical or subtropical climates.
Red witchweed is approximately 10 – 40 cm tall and the leaves are arranged in opposite pairs along the stem. The seeds are tiny and dust like and spread primarily within soil. A single plant can produce between 25,000 and 200,000 seeds.
The National Red Witchweed Eradication Response Program is cost shared between affected government and industry parties, that crosses both animal and plant-based industries.
The Red Witchweed Consultative Committee provides technical and scientific advice on the Queensland red witchweed eradication response. The Committee is chaired by the Australian Chief Plant Protection Officer. Membership is comprised of representatives from the Commonwealth, state and territory governments and affected plant and animal industry organisations.
NMG is the decision-making body for national plant pest eradication programs, including agricultural weeds. It is chaired by the Secretary of the Department of Agriculture, Water and the Environment. Membership comprises senior officials from Commonwealth, state and territory governments and affected industry organisations that are signatories to the Emergency Plant Pest Response Deed and the Emergency Animal Disease Response Agreement. This incident, however, is being managed under a deed-like arrangement.
The AGMIN delegated its decision-making authority to the NMG in January 2020, for the life of the red witchweed eradication program. The Red Witchweed Consultative Committee and the NMG will continue to oversee the red witchweed eradication program in Queensland.
What you need to do
Good biosecurity practices are vital to stopping the spread of weed seeds and other plant pests and diseases.
Please watch Biosecurity Queensland’s red witchweed video. It will show you how to identify red witchweed, and what you can do to stop it spreading.
Importantly if you see red witchweed on your property or in public areas (such as on roadsides) report it to Biosecurity Queensland on 13 25 23 or through the Exotic Plant Pest Hotline on 1800 084 881.
Farmers and graziers
For producers who suspect they have red witchweed:
- Report the plant immediately to Biosecurity Queensland on 13 25 23.
- Take photos of the infestation and store them until you are contacted by Biosecurity Queensland.
- Do not attempt to remove any flowering plants, as this may allow the weed to spread tiny, dust-like seeds.
- Don't move off-site any soil, machinery or products (including mulch) that might contain soil. This will help avoid spread of seeds to other properties.
- Seeds are tiny and can easily drop into the soil, enabling its spread. Therefore, keep the weed in place until Biosecurity Queensland can investigate.