Witchweeds are parasitic herbs that grow on the roots of host plants. They are serious weeds of maize, millet, rice, sugarcane, sorghum and legume crops.
Witchweeds are parasitic plants that:
Parasitic weeds like witchweed are among the most destructive and difficult-to-control weeds in agriculture. Worldwide, at least 11 species of witchweed are known to harm crops. The most damaging witchweed species are:
All Striga species except for the native Striga parviflora are Prohibited Matter in New South Wales (NSW). This native species can damage sugar cane and maize crops.
Witchweeds are annual parasitic herbs. They grow near the base of their host plants and can’t be seen until they emerge from the soil. This may take four to seven weeks for some witchweeds. They can flower and produce seed rapidly once they emerge. Most witchweeds are only 15-20 cm tall when fully grown, but some are up to 60 cm.
Host plants are often stunted, with symptoms resembling severe drought stress, nutrient deficiency or disease. The symptoms can appear before and after witchweeds emerge. A key sign of witchweed is host plant leaves shrivelling and wilting, despite moist soil.
Exotic witchweeds are not known to occur in NSW. Red witchweed (Striga asiatica) was found growing on several sugarcane properties near Mackay, Queensland, in 2013 and is the target of a national eradication program. It is a weed in 35 countries, including the United States.
Most witchweeds are native to tropical Africa, India, the Middle East and China. Even in their native range, witchweeds are troublesome and cause significant crop losses.
One native witchweed Striga parviflora has occasionally been found in woodlands on the north coast and central western slopes of NSW. This native witchweed has been found on sugar cane and maize crops in Queensland.
Witchweeds usually grow in intensive agricultural monocultures. However, they can also grow in grasslands, pastures and bushlands if their host plants are present.
Witchweeds grow best in well-drained soils, although some will tolerate wet areas.
Each plant can produce at least 50,000 tiny sticky seeds. The seeds can live in the soil for over 10 years. The tiny seeds are hard to detect during inspections and can easily be spread to new places by:
Witchweed seeds only germinate when exposed to certain chemicals produced by host plants. Witchweed seeds do not germinate when temperatures are below 20°C. The ideal temperature for germination of purple witchweed, red witchweed and cowpea witchweed is 30–35°C.
Please do not attempt to treat or dispose of this weed yourself. Report this plant if you see it anywhere in NSW by calling the helpline listed at the top of this page immediately. NSW DPI will lead an initial response for the treatment and disposal of the plant to stop it from spreading.
Do not touch the plants as they can be covered in small sticky seeds that are easily spread to new locations.
See Using herbicides for more information.
PERMIT 9907 Expires 31/03/2025
Fluroxypyr 333 g/L (Starane™ Advanced)
Rate: 300 to 600 mL in 100 L of water
Comments: Spot spray application
Withholding period: Do not graze failed crops and treated pastures or cut for stock food for 7 days after application. See label for more information.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate
The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.
|All of NSW||General Biosecurity Duty
All plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
|All of NSW||
A person who deals with prohibited matter or a carrier of prohibited matter is guilty of an offence. A person who becomes aware of or suspects the presence of prohibited matter must immediately notify the Department of Primary Industries
All species in the Striga genus are Prohibited Matter in NSW, except the native Striga parviflora