Yes, Ragwort is toxic to dogs!
Dogs accidentally consuming the Ragwort plants can show the following clinical symptoms: Vomiting, Prolonged Depression, Incoordination, Hypersalivaton, Sleepiness Or Excitation, Dilated Pupils, Low Body Temperature, Low Blood Pressure, Coma, Seizure And Death (In Rare Cases).
Ragwort consumption is also toxic to Cats and Horses.
Toxic Principles Of Ragwort: Pyrrolizidine alkaloids.
More Info About The Ragwort Plant
Scientific Name: Senecio species
Family: Compositae.
Also known as: Golden Ragwort, Tansy.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.