Damping Off
Disease · Commonly affects: Tomatoes, Peppers, Cucumbers, Squash, Beans, Cabbage and broccoli
Damping off is a common seedling disease caused by several soilborne fungi and fungus-like water molds, most often Pythium, Rhizoctonia, Fusarium, and Phytophthora, that attack seeds and tender young stems. It matters to gardeners because it can wipe out an entire flat or seedbed within a day or two, frequently before there is any warning that something is wrong.
How to identify it
Watch for seeds that never sprout, or for seedlings that suddenly flop over with a thin, water-soaked, pinched, or darkened spot right at the soil line. The stem at the surface looks brown and shriveled, the toppled plants never recover, and gaps appear in an otherwise even tray. In humid conditions you may also see fuzzy white or gray mold on the soil surface or on the collapsed seedlings.
Damage
The pathogens either rot seeds before they emerge or girdle the soft stem at the soil line just after sprouting, cutting off the flow of water and nutrients so the seedling wilts and collapses. Because seedling tissue has almost no natural defenses, losses in a small tray or row are often total, and the few plants that survive tend to stay stunted with damaged roots.
Prevention
Start seeds in clean, well-draining potting mix instead of garden soil, and scrub and sanitize pots, trays, and tools before each use. Sow at the recommended depth and thin seedlings so each has room, since crowding and stagnant, humid air strongly favor the disease. Wait until the soil has warmed before direct sowing, give seedlings bright light and steady air movement, and use fresh, high-quality seed of vigorous or disease-resistant varieties when they are available.
How to manage it
There is no cure once a seedling has collapsed, so promptly pull and discard affected plants along with the mix immediately around them to slow the spread. Water in the morning, ideally from the bottom or with a gentle hand, and let the surface dry slightly between waterings; improve airflow with a small fan and remove humidity domes once seeds germinate. Avoid overwatering and heavy feeding, keep trays off cold and wet surfaces, and reseed into fresh, sanitized mix rather than reusing contaminated material.
General guidance for US home gardens, focused on prevention and non-chemical control. For a confirmed diagnosis and options specific to your area, contact your local Cooperative Extension office. Page updated Aug 4, 2026.