Madagascar ragwort is likely to become the most serious threat to pastoral farming in New Zealand.  

A combination of factors mean it is on a different level in terms of its invasiveness and impacts:

• Major impacts on pasture productivity and high direct control and management costs. Documented declines in carcass weights of up to 35%, and 65% losses in milk solids per hectare, where infestations have taken hold.
• Toxic and can be fatal to stock, remaining toxic even in hay or silage, with no treatment available for affected animals.  
• Stock avoid grazing near the plant creating a ‘shadow effect’ which contributes to further spread and increasing pasture loss.  
• Rapid establishment; a single adult plant can produce 10,000 seeds within 6 weeks of germination.  
• Capable of germinating all year round following any warm rain event.  
• Difficulty and cost of control; there is no single agrichemical treatment that effectively controls all life stages without damage to beneficial pasture species. Repeated, carefully timed herbicide control, combined with changes to pasture management and pasture improvement are usually required to bring well-established infestations under control.
• Wind dispersed; while most seed drops relatively close to the parent plant, some of the seed can be blown long distances.
• Wide environmental tolerance; evidence from overseas and climate modelling  indicate that most of the North Island would be susceptible as well as large areas of the South Island.   

Madagascar ragwort originates from southern Africa and is a major weed in Australia and Hawaii. It is known as ‘fireweed’ in Australia, where it is a Weed of National Significance.

It is currently only known to be in Northland. Madagascar ragwort is currently widespread in the Far North, and is spreading rapidly in the mid-north. The current southern edge for confirmed infestations is Pakaraka, Kaikohe and Waima in the Hokianga.

It's distribution is likely to be significantly underestimated. As Madagascar ragwort  looks identical to the widespread weed gravel groundsel (Senecio skirrhodon), early invasions into new areas are more likely to go unnoticed.

Evidence from overseas and climate modelling indicate that most of the North Island would be vulnerable to invasion, as well as large areas of the South Island.

Prevention early detection and intervention is the best way to protect your farm 

If you do not already have Madagascar ragwort on your property, preventing a serious infestation from establishing will prevent the worst of the impacts.  

• Don’t bring it on to your farm. Good farm biosecurity is essential. 
• Ensure your hay and other fodder products are sourced from unaffected areas. 
• Ensure any machinery coming on to the farm is clean. 
• Utilise a ‘quarantine paddock’ for new stock brought on to the farm. Avoid moving stock from heavily affected areas. 
• If you see an unknown yellow flowering plant in or near your pasture, check it out and confirm its identification.   
• Ensure everyone on the farm knows what they are looking out for. Carry bags that can be sealed on farm vehicles so that any suspect plants can be carefully bagged then and there.
• If you are unsure of the identification, place a good-sized sample with flowers in a completely sealed bag, and bring it into your local Northland Regional Council office, or to your rural supplies Technical Advisor or farm consultant. Be very careful not to disturb seed heads or spread seeds when transporting it.  

Physical control

Hand weeding (pulling or grubbing) can be highly effective when done early in newly infested paddocks with few plants.  It needs to be done regularly to prevent plants seeding, or the seed bank and infestation size can quickly become unmanageable. 

• Pull carefully so they don’t snap off at the roots, ideally while they are young and before seed forms.
• Plants should be bagged with care taken not to disturb seedheads.
• If done poorly (when plants are seeding) it can spread seed further.
• Carry a bag with you on farm vehicles.
• Plants can be burnt but do not burn in domestic fireplaces due to toxicity. 
• When there is a large infestation hand weeding becomes less effective as these paddocks would already have established a seedbank.

Manual control options for large infestations are limited and can carry significant risk of worsening the issue if done poorly. Cut plant material also becomes more palatable to stock but remains toxic, and so require withholding periods to avoid stock deaths. In addition, pruned plants can become woody and more resistant to herbicides. 

Cultivation and soil disturbance triggers germination in pastures and can rapidly worsen infestation levels so is generally not recommended. As part of a carefully managed herbicide control programme it could be used to deplete seedbanks. 

The AgResearch report ‘Review of current control methodologies of Madagascar ragwort and control trial design’ provides more information on different manual control approaches as well as discussion on other pasture renewal and cropping considerations. 

Chemical control

Despite considerable trial work overseas there is no single agrichemical control method that effectively controls all life stages without impacting on desirable pasture species. Different approaches are required depending on the age of the plants, and the size and density of the infestation and seedbank. 

A large, well-established infestation will require a sustained and ongoing programme that is carefully timed around germination peaks, uses a rotation of chemical options, and is integrated with pasture management. Trials to refine and improve control methodologies are ongoing.  

The table below summarises the agrichemical methods most commonly in use in New Zealand for Madagascar ragwort control, their efficacy on the different life stages and impact on pasture. Application rates are not included here due to off-label considerations;  please speak with your rural supplier’s Technical Advisor or contact Northland Regional Council’s Pest Plant Biosecurity team for advice on your specific situation and application rates.

Further information on other agrichemical control options can also be found in the AgResearch report 'Review of current control methodologies of Madagascar ragwort and control trial design'.

General principles: 

• Seedlings and younger plants are far easier to kill than larger plants. Woody adult plants and flowering plants are the most difficult to kill. 
• Young plants can be boom sprayed with several options including 2,4-D based mixtures. 
• Some of the recommended products and mixtures will damage clover, and some will also impact grass.
• Adult plants need to be spot sprayed with harsher chemicals that will also damage clovers and sometimes grasses. 
• For well-established infestations it may be more beneficial to trade-off damage to desirable  pasture species in the short-term to more rapidly bring an infestation under control and protect other unaffected parts of the farm.
• Control programmes should be timed around germination peaks to target newly germinated seedling and juvenile plants while they are more susceptible and before they set seed. The main peak is usually in autumn, following the first rains, but can occur throughout most of the year, especially after warm rain events. Plants will usually flower 6 to 8 weeks after germination.
• Sprayed plants can take time to die; do not graze until completely dead and browned off to reduce the risk of poisoning stock.
• To prevent resistance from evolving, unrelated chemical groups with different modes of action should be rotated between and other forms of non-chemical management should be used to drive down the weed seed bank.
• The approach taken needs to be specific to your situation. Please speak with your Rural suppliers Technical advisor or farm consultant or contact the Pest Plant Biosecurity team at Northland Regional Council. 

Pasture and grazing management 

Madagascar ragwort grows in all types of soils but has a competitive advantage in low fertility soils and pasture damaged by drought or overgrazing. 

• Rotational grazing is more effective than continuous grazing. 
• Minimise soil disturbance as this provides an avenue for seedlings to germination and establish. 
• Sheep and goats can graze Madagascar ragwort – they are about ten times less susceptible to its toxins than cattle, however they can still be impacted by prolonged or high levels of exposure and milk can be affected.
• Cattle and horses are extremely susceptible to Madagascar ragwort poisoning. While cattle learn to avoid the plant, poisoning can still occur especially when plants are young and stock are unfamiliar with the weed, when it is in contaminated hay, or following control operations when cut or chemically treated material becomes more palatable. 

Biocontrol 

Biocontrol research on Madagascar ragwort has been underway in Australia for a significant period, however no suitable agents have been identified to date.  A  Biocontrol feasibility study for New Zealand was commissioned in 2022 which outlines the next steps for research, which includes genetic analysis to identify the original source population for the Madagascar ragwort in New Zealand, and further surveys in the native range to identify potential agents. Northland Regional Council is funding the genetic analysis as the first step in this process.