the rotting of seedlings, before or soon after emergence, caused by soil fungal species of Fusarium, Phytophthora, Pythium, and Rhizoctonia attacking at or near soil level —note 1. the name is derived from an association with damp weather or damp conditions —note 2. damping-off is the most common and probably the most serious nursery diseaseThis definition last updated 07/29/2008