Plants poisonous to horses in Australia and New Zealand

If you think your horse has eaten a poisonous plant, move it away from the source and call your vet straight away. Take a sample or photo of the plant if you can do so safely.

Horses usually avoid toxic plants when there's plenty of good feed. Trouble tends to start when feed is short, when horses are moved to unfamiliar paddocks, or when toxic plants end up in hay. The NSW Government notes that poisonings most often happen when animals are introduced to unfamiliar surroundings with toxic plants, or when other feed is scarce – and that pastures are more likely to contain toxic plants after floods, heavy rain and during drought (NSW Government – plants poisonous to livestock).

Some plants cause sudden death after a small amount. Others do damage slowly over weeks or months, and by the time signs appear the damage may be permanent. This guide covers the plants most often mentioned by Australian and New Zealand authorities. It isn't a complete list – learn what grows in your area.

Paddock weeds

Paterson's curse (Salvation Jane)

Echium plantagineum – purple, trumpet-shaped flowers in spring, common across southern Australia.

The NSW Government explains that Paterson's curse contains pyrrolizidine alkaloids, which cause liver damage that is irreversible, untreatable and ongoing. Horses are highly susceptible because they can't break down the alkaloids before they reach the liver (NSW Government). Signs can include weight loss, jaundice (yellowing of the gums or eyes), photosensitisation (sunburn-like skin damage on pale areas), and nervous signs such as blindness, wandering and head-pressing.

Ragwort

Jacobaea vulgaris (formerly Senecio jacobaea) – yellow daisy-like flowers in clusters.

Ragwort also contains pyrrolizidine alkaloids. Massey University's poisonous plants database explains that chronic poisoning builds up over weeks to months, so signs are delayed. Early signs include weight loss, poor appetite and constipation; later signs include jaundice, photosensitisation and abdominal pain. There's no specific treatment, and once signs appear the outlook is poor (Massey University – ragwort).

Massey also warns that:

• Hay-making doesn't destroy the toxin, so contaminated hay remains dangerous.
• Dead or wilted plants are still toxic and become more palatable, so sprayed plants should be removed from the paddock.

Flatweed (catsear)

Hypochaeris radicata – yellow, dandelion-like flowers on a flat rosette.

Flatweed is linked to Australian stringhalt, where the hind legs jerk upwards as the horse walks (NSW Government). Agriculture Victoria says stringhalt is most likely in autumn, especially during or after drought (Agriculture Victoria – winter care). Call your vet if you suspect it. NSW recommends removing the whole plant and taproot in small areas, using a suitable herbicide in larger areas, and building a competitive pasture.

St John's wort

Hypericum perforatum – golden-yellow flowers with black dots on the petal edges, late spring to summer.

The whole plant is poisonous to grazing animals, including horses. Repeated grazing can cause photosensitisation – sunburn on pale, unpigmented skin such as the nose and face. If you suspect it, NSW advises moving animals to a paddock free of the plant with good shade (NSW Government).

Other weeds to watch for

Agriculture Victoria lists Paterson's curse, ragwort, bracken fern, flatweed, marshmallow and St John's wort among common weeds poisonous to horses, and notes that weeds often flourish after autumn rain following a dry summer (Agriculture Victoria – winter care). NSW also lists heliotrope, which contains the same group of liver toxins as Paterson's curse (NSW Government).

In New Zealand, NZQA's equine-care unit standard on poisonous plants requires knowledge of at least ragwort, hemlock, castor oil plant, tutu, Mexican devil weed and potato (NZQA unit standard 6612).

Trees, shrubs and garden plants

Garden plants are a real risk on small properties, where horses can reach over fences or are fed garden clippings. NSW warns that garden clippings containing toxic plants can be fatal to livestock (NSW Government). Never feed lawn or garden clippings – Victoria's Code of Practice lists lawn clippings and poisonous plants among harmful feeds (Code of Practice).

According to the NSW Government (NSW Government):

• Oleander and yew are toxic to horses and can cause sudden death from heart failure.
• Sugar gums and Prunus species (such as ornamental and stone-fruit trees) contain cyanide and can cause sudden death within hours.
• Foxglove can also cause fatal heart problems.
• Rhododendrons and azaleas can affect the digestive and respiratory systems.

NZQA's unit standard also lists laburnum, cherry laurel, ivy, box, ngaio, macrocarpa and avocado among trees and shrubs horse carers should recognise as potentially poisonous (NZQA 6612).

Black walnut

Black walnut is mostly a concern as bedding. The MSD Veterinary Manual lists black walnut shavings as a cause of laminitis (MSD Veterinary Manual). See horse bedding types.

Signs of plant poisoning

Signs vary widely by plant, but call your vet if you see:

• Sudden collapse, trembling, staggering or seizures
• Colic, diarrhoea or drooling
• Weight loss, poor appetite or dullness over weeks
• Yellow gums or eyes (jaundice)
• Sunburn-like reddening or peeling on pale skin (photosensitisation)
• Unusual behaviour – head-pressing, wandering, blindness
• An abnormal, high-stepping hind-leg gait (stringhalt)

Knowing what's normal for your horse helps – see signs of a healthy horse.

Protecting your horses

Know your paddocks

Walk your paddocks regularly, especially after rain, in autumn, and when moving horses to new ground. Identify any plant you don't recognise. The NSW WeedWise database is a good identification tool (NSW WeedWise), and your local council or land services office can help.

Keep pasture competitive

Healthy, dense pasture leaves less room for weeds and gives horses better things to eat. NSW recommends competitive perennial pasture as part of managing weeds such as flatweed and St John's wort (NSW Government). See paddock management.

Remove and control weeds safely

• Pull small infestations, removing roots, and take them off the property in bags.
• Remove sprayed plants where needed – wilted ragwort is more palatable and still toxic (Massey University).
• Follow herbicide labels, including withholding periods for grazing.
• Victoria's Code says paddocks and yards should be kept free of noxious plants (Code of Practice).

Check fences and boundaries

Make sure horses can't reach garden plants, hedges or neighbours' trees. Clear fallen branches and leaves from paddocks after storms.

Check your hay

Buy hay from suppliers you trust, and inspect each bale for weeds before feeding. Toxins in plants such as ragwort survive hay-making (Massey University). See buying hay.

Don't let horses get hungry

Provide hay when pasture is short. Hungry horses are more likely to eat plants they'd normally avoid (NSW Government).

Find an equine vet near you on horse.work, and keep their number handy.

FAQ

What is the most poisonous plant to horses in Australia?

It depends on the region. Paterson's curse is one of the most widespread problem weeds, causing irreversible liver damage (NSW Government). Oleander and yew can kill quickly in small amounts.

Will horses eat poisonous plants?

Usually only when other feed is short or the plants are unfamiliar. Wilted or dried plants can be more palatable (Massey University).

Is ragwort still poisonous in hay?

Yes. Massey University notes that hay-making doesn't reduce the toxin (Massey University).

What causes stringhalt in horses?

Australian stringhalt is associated with grazing flatweed (catsear) and some other weeds, most often in autumn after dry conditions (NSW Government; Agriculture Victoria).

Can liver damage from Paterson's curse be treated?

No. NSW describes the liver damage as irreversible and untreatable (NSW Government). Prevention is the only protection.