Damping off is a term used for the sudden death of new plant seedlings. It can be caused by any of a handful of fungal diseases, including the pathogens Pythium, Phytophthora, Rhizoctonia spp., Fusarium spp., Sclerotinia, and Botrytis.
When young seedlings seem to be growing healthy one day and dying the next, it is probably being caused by damping off. Damping off can affect the stems of seedlings both below the soil line and above. Some seedlings may start to grow and suddenly whither. Others will have stems that appear pinched or broken, causing them to collapse while they still have their cotyledons attached. You may see some gradual discoloring or it may happen very suddenly. Often it appears the seedling has been pinched off at the soil line.
Seedlings may appear to be wilting, even when kept watered. Even poor germination may be attributable to damping off. If your seedlings were growing along fine and suddenly wilt and die, it's a good bet they have succumbed to some form of damping off disease.
What to Do If Your Seedlings Get Damping Off
There is no cure for damping off, once it occurs. The tiny seedlings die so quickly, you probably would not have time to help them if you could. That's why it is important to try and avoid the problem altogether, with the following prevention practices.
Damping off spreads rapidly. If you should spot signs of damping off, remove those seedlings immediately and isolate all remaining seedlings. Do not place them in the compost, as the pathogens can linger in the soil.
- Use a sterile potting mix, rather than soil from your garden. The pathogens that cause damping off can live in the soil, and outdoor garden soil can harbor all kinds of fungus spores.
- Start with clean pots. Even the small amount of soil clinging to plant pots is enough to provide a safe harbor for fungal spores. If reusing pots, sterilize in 1 part bleach to 9 parts water. Soak pots for 30 minutes, then rinse with fresh water.
- Don’t crowd your seedlings. Be sure to leave room between them for air circulation. Fungal diseases and mold favor damp conditions.
- Water seedlings from the bottom, by placing the container in a tray of water. This keeps the seedling itself dry and less susceptible. Do not let the tray stand in water, though--remove excess water after the soil is moist.
- Add a thin coating of sand or gravel on top of the potting soil, to keep the surface relatively dry. The soil underneath will remain moist, even if the sand or gravel dries out.
- Don’t overwater your seedlings or leave them sitting in water. Drain off any excess.
- If possible, create a breeze by placing a small fan nearby and turning it on periodically each day. This will help increase air flow for your seedlings.
- Give your seedlings plenty of heat and light, so they germinate and grow quickly. Many pathogens prefer cool soil, so a heat mat set at 70-75 degrees may help prevent damping off.
Remove any affected plants or trays of plants immediately. Damping off will quickly spread to nearby plants.
- University of Connecticut IPM
- University of Arizona Cooperative Extension
How to Prevent Seedling Damping Off. University of Minnesota Extension