Damping off
Also known as Seedling damping-off, Wire stem
In short
Damping off is the death of seeds and young seedlings caused by several soil-borne organisms, including Pythium, Phytophthora, Rhizoctonia, Fusarium and sometimes Botrytis. It is worst in wet, cool, crowded and poorly ventilated conditions. Clean media, clean containers and careful watering prevent most cases.
How it looks
Before emergence, seeds rot or seedlings never appear. After emergence, seedlings collapse and fall over at soil level, where the stem is thin, pinched or discoloured; some become wiry ('wire stem'). Collapsed seedlings may be covered in a whitish fungal growth. Losses often occur in roughly circular patches that spread through a tray.
Signs
Gaps in rows or trays, seedlings toppling over while leaves are still green, brown lesions on stems at soil level, and rotten roots.
Life cycle
The causal organisms live in soil, unsterilised mix, dirty containers and stored rainwater, and attack soft seedling tissue. They spread through wet media and water.
What favours it
High humidity, poor air circulation, overwatering, crowded sowings, and low temperatures and light levels (for example early spring sowings indoors).
Prevention
- Sow into fresh, sterile seed compost, not garden soil or reused mix.
- Clean trays, pots and tools before use.
- Sow thinly so seedlings are not crowded.
- Water with clean mains or tap water rather than stored rainwater, and avoid overwatering.
- Ventilate propagators and give seedlings good light.
Treatment
Start with the first step and move down only if the problem persists.
- Remove and discard affected seedlings and the mix around them promptly.
- Increase ventilation and let the surface dry slightly between waterings.
- Resow in fresh media in clean containers if losses are heavy.
- Some countries (for example the UK) have no fungicides available to gardeners against damping off; where products are permitted, follow the product label.
Pros and cons
Cons
- Can wipe out a whole sowing within days.
- Several different pathogens are involved, so one product rarely covers all of them.
Look-alikes
- Etiolation
- Etiolated seedlings are long and pale from low light and may flop, but the stem base is not rotted.
- Botrytis
- Botrytis shows grey, dusty fur on dead tissue; it can also be one cause of damping off.
- Fungus gnats
- Fungus gnat larvae can damage seedling roots; look for tiny dark flies over the mix.
Affected plants
Seedlings of almost any plant, including vegetables, bedding plants, herbs such as basil, tree seedlings and orchid seedlings.
Related
Sources
Written in our own words from these sources. Check a product label before using any treatment.