Damping off is a disease that affects seeds (pre-emergence) and young seedlings (post-emergence). When severe, it can cause significant crop loss for greenhouse growers.
Pre-emergence damping off causes seeds to die before or very shortly after germination. What appears to be poor germination may in fact be the death of seeds or hypocotyls below the soil surface. Post-emergence damping off can cause root rot and/ or stem lesion and rapid death of seedlings. Lesions produce constricted areas on the stems, usually at soil level, and severely afflicted plants will fall over and die. Root rot may or may not be present. Foliar symptoms are sometimes also seen.
Damping off can be caused by several types of fungi. Pythium and Rhizoctonia are the most common genera, while occasionally Phytophthora, Fusarium, Alternaria, Sclerotinia, or Thielaviopsis may be the culprit. All of these fungi are soil-borne; in addition, Alternaria can be seed-borne.
Several cultural control methods can help prevent damping off:
- Use fresh seed every year.
- Do not seed flats too heavily. Thin seedlings to increase air circulation within flats.
- Fans improve air circulation and keep plant surfaces dry, decreasing the chances of fungal infection.
- Do not over-water.
- Improve drainage by using a good seedling mixture. Do not put flats directly on the greenhouse floor: water pools on non-porous flooring, and fungal propagules live there.
- Cool temperatures generally favor damping-off. Use a heated greenhouse or seedling mats.
- Excess N retards tissue maturation and encourages tender growth, which is more susceptible to fungal infection.
- Use seeds treated with a fungicide. (Caveat: seed treatments in general are only effective for about 2 weeks after seeding.)
- Practice good greenhouse sanitation. Discard any diseased flats.
- Control fungus gnats and other insects that can transport fungi among plants.
Several fungicides are labeled for use to prevent damping-off. Detailed information on these can be found in the New England Greenhouse Floriculture Guide.
Photos: Damping off of Catharanthus seedlings (Rhizoctonia)
Damping off of Begonia seedling (Rhizoctonia)
Damping off of Vinca (Phytophthora)
Angela Madeiras, UMass Extension Plant Diagnostic Laboratory
