Yes, mums (Chrysanthemums) are poisonous to dogs. Ingesting any part of the mum plant can cause symptoms such as vomiting, diarrhea, drooling, hypersalivation, incoordination, and dermatitis in dogs. The toxicity comes from compounds like sesquiterpene lactones and pyrethrins, which are irritants to pets. Even dried mums can be harmful. If a dog ingests mums, it is important to contact a veterinarian promptly as the poisoning can lead to serious symptoms including agitation, shaking, respiratory issues, seizures, or worse in severe cases.