Mushroom toxicity undoubtedly happens more often in dogs than is reported because many of these poisonings go unrecognized for what they actually are.
Here is a list of some highly poisonous mushrooms for dogs.
False Morales
March - May
Death Caps
July - October
Panther Caps
July - November
Fools Webcap
August - October
Fly Agaric
August - November
Funeral Bell
September - November
The symptoms most frequently seen in dogs are lethargy, staggering, panting, whining, dizziness, salivation, vomiting, tachycardia, and collapse.
While there are many mushrooms that aren't poisonous it's best to keep your yard clear of mushrooms and any potential dangers.
If you suspect your dog has ingested something harmful or poisonous please bring them to your nearest emergency veterinarian immediately.