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Integrated Pest Management Program

Department of Plant Science and Landscape Architecture, Department of Extension

Fact Sheets > Greenhouse > Diseases

Damping-off of Ornamental and Vegetable Seedlings

Damping-off is a common disease of germinating seeds and young seedlings. It may be found in greenhouses that grow vegetable or ornamental transplants. Several fungi or fungi-like organisms are capable of causing damping-off especially Pythium and Rhizoctonia. But, Alternaria, Sclerotinia, Botrytis and Fusarium can also occasionally cause damping off.  

These soil-borne fungi generally do not produce air-borne spores but are easily transported from contaminated field soil or contaminated soil in greenhouse “dirt” floors to pathogen-free soil in containers via infected tools, hose ends, water-splash and worker’s hands. Some fungi such as Alternaria are seed borne.

Favorable Conditions

Damping off can be a problem if the growing media stays wet too long. Excessive overhead misting or condensation drip from overhead onto the media can also promote damping off. (However, Rhizoctonia can cause disease when conditions are somewhat drier.) Low media temperatures (below 68˚F) before seeds germinate can also promote damping off. Overcrowded seed flats also favor damping off diseases.

Young seedlings are most susceptible to damping-off. However, later in the crop cycle, the same pathogens may cause collar rot or “wire stem” – which is an off-color, twisted and constricted stem. Infected plants may later develop root and stem rot, too.

Symptoms

Fungi may attack germinating seeds or young seedlings.

Symptoms of damping-off may include:

  • seedlings failing to emerge (pre-emergence damping off)
  • wilting, often with a stem lesion that appears water-soaked or dark, necrotic and sunken at the soil line (post emergence damping off)

When seedlings are planted in flats, pathogens usually spread radially from a central point of origin so plants often die in a circular pattern. In plug trays, infected plants may be more randomly affected as the disease is spread by splashing water. Seeds that are germinated in poorly drained, cool soils are especially susceptible. Young plants that do emerge are weak and often wilt at or below the soil line. Stems of these plants may shrivel and become dark and woody (wirestem or collar rot). The plants may not collapse but remain stunted and die after transplanting.

Seeds may also not germinate if the seed is old or if conditions have not been favorable for germination. If the seeds have germinated, but the emerging shoot is water soaked or decayed, fungi are most likely the cause. Roots may or may not be decayed.

If tender young seedlings are over fertilized, roots appear shriveled and desiccated, as the plants die from high salts. Hot water, heat stress, lack of water and chemical sprays can also cause tender young seedlings to die.  

Management: Damping-off must be prevented because it is difficult to stop once symptoms occur. There are several strategies to prevent damping-off. Focus on proper sanitation practices, combined with cultural and environmental management.

Proper Sanitation Practices

  • Use only certified disease-free seed from reputable seed companies.
  • Use fungicide-treated seed.
  • Use commercially available soilless potting media that are free of damping off fungi.
  • Use pasteurized soil, or properly produced compost-based mixes.
  • Disinfect all flats, cold frames, pots and tools.
  • After disinfection, do not contaminate cleaned flats by placing them on a dirty greenhouse floor or using dirty tools.
  • Do not reuse plug trays that had diseased plants.
  • Discard entire infected flats.
  • Do not just discard seedlings with symptoms of damping off. Seedlings may appear healthy but can carry infected soil and develop wirestem or root rot as they get older.

Encourage Seedlings to Grow Rapidly

  • Incorporate biological fungicides into your soilless mix or apply biological fungicides as a drench at planting.
  • Fill flats with pre-moistened growing media to avoid compaction. Lightly fill and brush containers.
  • Germinate seed under conditions that will ensure rapid emergence, such as with the use of bottom heat (70-75˚F).
  • Avoid planting seeds too deeply, which stresses the seedlings.
  • Provide adequate light for rapid growth.
  • To avoid compaction, do not stack or “nest” filled trays or pots.

Avoid favorable conditions for the pathogens (cold, wet conditions) 

  • Avoid overwatering, excessive fertilizer, poor air circulation, and careless handling. 
  • Avoid planting seeds too densely, which reduces air flow around the plants.
  • Keep greenhouse temperatures warm with low humidity. Condensation on the plastic causes drips which can then lead to damping off.

If damping off occurs, treating with a broad spectrum fungicide may be an option. However, tender young seedlings are more susceptible to plant injury from fungicide treatments (phytotoxicity) than more mature plants. Certain species or cultivars may be more sensitive to injury from fungicide treatments. If so, spot treatments may be needed, avoiding sensitive species or cultivars. 

For the latest information on registered fungicides, see New England Greenhouse Floriculture Guide, A Management Guide for Insects, Diseases, Weeds and Growth Regulators.

Available from New England Greenhouse Conference and Expo and the UCONN CANR Communications Resource Center.
References: 

Daughtery, M. L., R. L. Wick and J.L. Peterson. 1995. Compendium of Flowering Potted Plant Diseases.  APS Press, St. Paul, MN

Grubinger, Vern. Prevent Damping Off. Tips and Tactics to Keep your Greenhouse Clean. Growing Magazine

Kleczewski, N.M. and D. S. Egel, 2011. Sanitation for Disease and Pest Management. Purdue Extension HO-250_W    

Moorman, G.W Damping off. Pennsylvania State University Cooperative Extension. Plant Disease Fact sheet.

Wick, R. L. 1998. Damping-Off of Bedding Plants and Vegetables. University of Massachusetts.

By: Leanne Pundt, Extension Educator, University of Connecticut. November 2011.

The information in this document is for educational purposes only.  The recommendations contained are based on the best available knowledge at the time of publication.  Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.  The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.