How To Deal With Damping off in Your Irish Garden
What is Damping off?
Damping off is a common and frustrating disease that affects newly germinated seedlings, causing them to collapse and die shortly after emergence. It is caused by several soil-borne fungi and oomycetes, including Pythium, Phytophthora, Rhizoctonia and Fusarium species. These organisms attack the soft, vulnerable stems of seedlings at soil level, causing them to rot and collapse. Damping off is most prevalent in cool, wet conditions with poor air circulation — precisely the conditions found in many Irish greenhouses and windowsills during the spring sowing season. Overwatering, overcrowding, poor drainage and using unsterilised compost all increase the risk.
Damage Caused by Damping off
Damping off causes seedlings to topple over at soil level, with the stem appearing water-soaked, pinched and dark at the point of collapse. The disease can appear before germination (pre-emergence damping off, where seeds rot before sprouting) or after emergence (post-emergence damping off, where established seedlings collapse). Whole trays of seedlings can be wiped out within 24-48 hours once the disease takes hold. The fungal organisms spread rapidly through wet compost, moving from seedling to seedling. All types of seedlings are vulnerable, though brassicas, lettuce, tomatoes and flowers are most commonly affected.
How to Prevent Damping off
Use clean pots and seed trays — wash in hot soapy water and rinse with dilute disinfectant. Use fresh, sterile seed-sowing compost, not garden soil which harbours damping off organisms. Sow seeds thinly to avoid overcrowding. Water from below by standing trays in water rather than watering from above. Ensure good air circulation around seedlings. Do not overwater — compost should be moist but not waterlogged. Use vermiculite or perlite as a seed covering, which helps keep the surface dry. Remove any collapsed seedlings immediately.
How to Treat Damping off
There is no effective treatment once damping off has struck — affected seedlings cannot be saved. Remove all collapsed seedlings and the surrounding compost immediately to prevent spread. If some seedlings in the tray are still healthy, move them to fresh compost in clean pots, spacing them well apart. Improve air circulation and reduce watering. Water remaining seedlings with a dilute copper fungicide solution as a preventive measure. For subsequent sowings, use fresh compost, clean containers and follow all preventive measures.
Damping off in Ireland
Damping off is extremely common in Ireland, where the cool, damp spring climate creates challenging conditions for raising seedlings. Irish gardeners starting seeds on windowsills, in greenhouses and in polytunnels during March and April are particularly vulnerable. The relatively low light levels and cool temperatures of the Irish spring slow seedling growth while favouring the pathogens that cause damping off. Heating propagators to speed germination and then moving seedlings to good light helps reduce the risk. Using sterile compost and clean containers is essential in Irish conditions.
Plants Affected by Damping off
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