Yellow Star-thistle
Centaurea solstitialis
Horse
Moderate
Remove access and monitor the horse; call at the first sign. Ingestion of significant amounts (around 10% of body weight) over a prolonged period can cause neurological and hepatic symptoms.
Equio informs, it does not diagnose. When in doubt, call your vet.
What to do now
- Antidote
- No specific antidote known. Treatment is symptomatic and supportive.
- Time to signs
- Several weeks to several months of regular ingestion.
- Prognosis
- Variable. Mild cases may recover with supportive care. Severe cases with significant neurological or liver damage can be difficult to treat and have a guarded prognosis.
- Immediately remove the horse from the contaminated area.
- Contact an emergency veterinarian.
- Do not allow the horse to eat until advised by a veterinarian.
Its ID card
- Height
- 30-120 cm
- Flowering
- Summer (June to September).
- Toxic parts
- All parts of the plant, particularly young shoots and flowers.
- Toxin
- Unknown alkaloids, potentially sesquiterpene lactones.
- Habitat
- Dry grasslands, fallow land, roadsides, cultivated fields, disturbed areas, often on calcareous soils.
- Soil indicator
- Prefers well-drained soils, often calcareous or sandy.
- Regions
- Southern Europe, North Africa, California, Australia, New Zealand
- In hay
- Yes — stays toxic once dried
- Palatability
- Low, but may be consumed inadvertently, especially when the plant is young or in cases of forage shortage.
When the risk rises
Spring and summer, when the plant is actively growing and flowering.
Spotting it in the field
Other Centaurea species, but the characteristic spines on the bracts are distinctive. — smell : slightly aromatic, but not particularly strong.
- Annual or biennial plant reaching 30 to 120 cm in height.
- Branched, winged, and spiny stems.
- Basal leaves lobed, stem leaves narrow and spiny.
- Bright yellow flowers, solitary, terminal.
- Floral bracts modified into rigid, yellow spines, resembling stars.
- The entire plant is often covered with fine white pubescence.
Signs to watch for
Primarily chronic, due to repeated ingestion over a long period.
Dose : Not precisely determined, but chronic ingestion is more concerning.
- Abnormal movements (Chesterfield disease or 'horse sickness')
- Tremors
- Incoordination
- Falling
- Constipation
- Colic
- Weight loss
- Liver damage
Who is affected
Other species : None known.
In pregnant mares : not specifically documented, but severe intoxication can affect the mare's general health.
Getting rid of it
Method : Manual or mechanical pulling, use of selective herbicides if necessary. Avoid oversowing with competitive grasses.
- Regularly inspect pastures and remove the plant.
- Ensure adequate feeding to prevent horses from grazing on undesirable plants.
- Avoid overgrazing pastures.
- Identify and manage areas where the plant is present.
Frequently asked questions
Can Equio identify Yellow Star-thistle from a photo?
It can help organize visual clues, but plant identification must remain cautious when horse health is at stake.
Is Yellow Star-thistle dangerous in hay?
This entry flags hay vigilance. Isolate suspicious forage and ask for professional advice if exposure is possible.
This page is informational. If ingestion is likely, if signs appear, or if the horse is fragile, contact a veterinarian immediately.