Seedling Damping Off GD 9
Ann Hazelrigg, Plant Diagnostic Clinic Coordinator
One of the first problems of the season in the home vegetable garden is the disease known as pre-emergence or
post-emergence damping-off. Fungi in the soil attack seeds and seedlings as they begin to germinate and grow.
Pre-emergence damping-off occurs when the seed or seedling dies before it reaches the surface, whereas
post-emergence damping off occurs when the seedling emerges and grows to a height of an inch or two, then wilts and
dies. Plants that are attacked by these fungi but do not damp-off are often stunted. A constricted stem at or just below
the soil line is a sign that the plant underwent a fungus attack during the growing season.
Damping-off is caused by several fungi including the water molds such as Phtophthora and Pythium. These fungi
occur in all soils, are water loving organisms, and thrive in wet or poorly drained soils. Slow-growing or weak plants
are more susceptible to damping-off than vigorous fast-growing seedlings. If the plant can grow roots faster than the
fungus can decay them, the plant will survive and be healthy.
Seed planted in soil too cold for proper germination nd fast growth will be subject to damping-off. Follow directions
on seed packets as to time of planting. Avoid wet low spots as gardening sites. When possible, provide adequate
drainage to prevent standing water accumulation in the seedbed. Do not use old seed. If seed is held over from the
previous year, test a sample for its ability to germinate prior to planting.
A fungicide can be used as a seed protectant. This method is used to coat the seed surface with a fungicide effective
against soilborne plant pathogens responsible for seed rot and damping-off. In the soil the fungicide provides a
protected barrier around the seed and gives the newly emerging seedling a few days start before fungi can attack.
Seed often can be purchased pre-treated with fungicide. Packages having seed treatment will be clearly marked. If not
already treated, a fungicide can be added by measuring a quantity of chemical the size of two match heads into each
seed packet. Close the packet, shake vigorously, and plant directly from the packet.
Damping-off commonly occurs in flats planted for transplants. To prevent this problem, soil can be heated to kill
pathogenic organisms in the soil. Place soil 3-4 inches deep in a pan and preheat the oven to 200o F. Place the soil in
the oven and check the soil temperature occasionally with a meat thermometer. When the soil temperature reaches
160o F, turn off the stove and keep the oven door closed for 30 minutes. This procedure will pasteurize the soil rather
than sterilize the soil. Soil that is sterile is much more susceptible to recontamination by plant pathogens. Do not mix
unpasteurized soil with pasteurized soil. Surface sterilize tools, work tables, and containers with a weak solution of
sodium hypochlorite (1 part household bleach + 9 parts water) to prevent contamination of soil.
For current fungicide recommendations, refer to Brieflet 1158.
Based on material developed in 1992.