Yes, Cowbane is toxic to dogs!
Dogs accidentally consuming the Cowbane 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).
Cowbane consumption is also toxic to Cats and Horses.
Toxic Principles Of Cowbane: Cicutoxin.
More Info About The Cowbane Plant
Scientific Name: Cicuta species
Family: Apiaceae.
Also known as: Water Hemlock, Poison Parsnip.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.