Damping-off is the rotting of seeds in the soil and destruction of newly emerged seedlings by fungi.

The entire seed may decay before germination or the seedling may rot just below the soil line. Older plants are usually not killed but often develop stem and root rots. The fungi most often causing this disease belong to the genus Pythium. Fusarium and Rhizoctonia species can also cause damping-off.

Conditions favoring damping-off:

• Excessive soil moisture and excessive overhead misting.
• Low soil temperatures before germination (below 20°C or 68°F).
• High soil temperatures after emergence (above 25°C or 77°F).
• Overcrowded flats or seedbeds.

Control in the greenhouse:

Start seeds and cuttings in pasteurized soil or a soilless mix using only sterile flats or pots. Potting soil can be pasteurized by heating it to about 180°F and holding it at that temperature for 30 minutes. Most commercially available soilless potting mixes are free of damping-off fungi and do not need to be treated.

Do not contaminate the soil, pots, or flats by placing them on dirty floors or benches or by using dirty tools.

Supply bottom heat so that the soil in the containers is 70-75°F (22-24°C).

Maintain even soil moisture conditions during germination and seedling development.
Buy fungicide-treated seeds or treat the seeds yourself. Certain fungicides can inhibit root formation. It is best to avoid the applying pesticides to seedlings and cuttings. If using a fungicide is unavoidable, it is suggested that only a portion of the crop be treated the first time this is done. If no inhibition of germination or rooting is noted, it is safe to use that specific chemical on that variety of crop.