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Damping Off Disease

Damping-off is a common disease of seedlings. It causes extensive losses to growers through death of seedlings or production of low-quality plants that perform poorly in the field. The disease can be avoided and controlled by practicing effective preplant control measures.

Damping-off is primarily caused by fungi present in the growing medium. The fungi include species of Rhizoctonia, Pythium, Fusarium, Phytophthora, Sclerotinia, Sclerotium, Botrytis, and others. Germinating seed and seedlings, especially weak ones, are vulnerable to attack by these fungi during periods of unfavorable growing conditions. Species of Pythium, Sclerotinia, and Phytophthora are more likely to cause damping-off in cool, wet soils; whereas species of Rhizoctonia, Fusarium and Sclerotium rolfsii may cause damping-off under warmer and drier conditions.

True damping-off may be confused with plant injury caused by excessive fertilization, high soluble salts, drowning in wet soil, desiccation in dry soil, and death of seedlings from excessive heat, cold, fuel fumes, or chemical injury. This type injury often damages the leaves and upper stem before the roots are affected.

Controlling Damping Off Disease

The best control of damping-off is to avoid it altogether. Once damping-off has started in a plant bed or seedling flat, it may be difficult to control and it is probably better to dispose of the growing medium for small planting beds.

The general methods used to prevent damping-off consist of :

  1. Proper soil preparation and management that includes good soil drainage, structure, aeration, water-holding capacity and plant nutrition by including proper amounts of nutrients based on a reliable soil test report.

  2. Proper soil treatment with heat or chemicals to reduce the level of fungi that cause damping-off.

  3. Use of fungicide-treated seed with high germination rates.

  4. Sowing at the correct seed rates to avoid thick plant stands, poor air movement and low light intensity.

  5. Planting seeds at the proper depth and insuring correct soil temperature for rapid seed growth.

  6. Avoid reinfesting treated soil with these fungi. Many outbreaks of damping-off can be attributed to poor sanitation practices after treating the soil. For bedding plant operations, it may be more practical to buy a sterilized soilless mix and eliminate steps 1 and 2 above.