Yes, Lambkill is toxic to dogs!
Dogs accidentally consuming the Lambkill 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).
Lambkill consumption is also toxic to Cats and Horses.
Toxic Principles Of Lambkill: Grayanotoxin.
More Info About The Lambkill Plant
Scientific Name: Kalmia augustifolia
Family: Ericaceae.
Also known as: Sheep Laurel.
The answer is based on information found on The American Society for the Prevention of Cruelty to Animals (ASPCA) website.