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Damping Off

Plant disease

Description​

Damping off is a disease of seeds and young seedlings, not a single organism with one scientific name. It can be caused by several soilborne pathogens, including Pythium and Phytophthora species (water molds) and fungi such as Rhizoctonia solani and Fusarium species. Seeds may rot before they emerge, leaving gaps in a tray or seedbed. Seedlings that do emerge can develop decayed roots or a soft, constricted stem at the soil line, then topple over. Others wilt or grow poorly before collapsing. The disease spreads most readily in crowded, persistently wet seed-starting conditions, particularly when drainage and airflow are poor. Young seedlings are most vulnerable; established plants are generally less susceptible. A fallen seedling cannot recover once its stem has rotted. Because different pathogens cause similar signs, the everyday name describes the problem rather than identifying its exact cause.

Symptoms​

  • Seedlings collapse at soil level
  • Soft or rotting stems
  • Brown, mushy roots
  • Wilting
  • Stunted growth

How to Identify​

Look for patches of missing seedlings or seedlings that suddenly fall over. At the soil line, an affected stem is often thin, discolored, and soft; roots may be brown and decayed. Gently uncover a seed from an empty spot: a rotted seed suggests pre-emergence damping off, while a firm, intact seed may simply have failed to germinate. Cutworm damage usually leaves a stem cleanly severed rather than pinched and rotting. Drought can also cause wilting, but the growing mix will be dry and stems will not show a decayed collar. Several pathogens look alike, so a laboratory test is needed to identify the exact cause.

Prevention​

Start seeds in fresh, well-draining seed-starting mix and clean trays; avoid reusing garden soil or contaminated potting mix. Use containers with drainage holes, sow at the recommended depth, and thin crowded seedlings. Water enough to keep the mix evenly moist, not saturated, and empty standing water from trays. Water from below when practical, then let the surface begin to dry. Provide gentle airflow and the temperature and light appropriate for the crop so seedlings grow steadily rather than remaining weak and slow-growing. Remove plant debris and clean tools between batches. If damping off has occurred, discard the affected mix and wash and disinfect reusable containers before sowing again. These steps reduce risk but cannot guarantee that every seedling will be disease-free.

Treatment​

Remove collapsed seedlings promptly, along with the immediately surrounding mix, and discard them. Do not expect seedlings with rotted, constricted stems to recover. For those still healthy, stop leaving water in the tray, improve drainage and gentle airflow, and let the mix surface dry slightly between waterings without drying out the roots. Separate unaffected trays from the affected batch. If losses continue, carefully move healthy seedlings into fresh seed-starting mix and clean containers, taking care not to carry over contaminated mix; delicate seedlings may not survive transplanting. Avoid applying household remedies to seedlings. A biological product labeled for seedling disease control may help protect remaining plants, but results vary and it will not repair damaged stems. As a last resort, consider a fungicide specifically labeled for damping off on the crop and for the suspected pathogen. Products effective against fungi do not necessarily control the water molds that also cause damping off; follow the label exactly.

Plants Affected​

Amaranth, Beet, Cilantro, Coriander, Dill, Honduran Mahogany, Indian Sandalwood, Lisianthus, Sandalwood, Savory, Snapdragon, Spinach, Statice, Sweet Pea, Swietenia

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