⚠ CriticalDamping-off girdles young stems at the soil line with a dark water-soaked lesion, toppling seedlings and cuttings that were healthy days before — a disease of wet, non-sterile media.
Rhizoctonia Damping-Off in Seedlings & Cuttings
Commonly affects: Aroid seedlings & cuttings — Philodendron, Monstera, Syngonium, Alocasia
Young seedlings and freshly potted cuttings collapse suddenly, with a dark, water-soaked, pinched lesion girdling the stem at the soil line. The tissue above the constriction topples over while still green, and fine brown fungal threads may be visible on the stem base or substrate. Germinating seeds may rot before emerging.
Potential Causes
- 1Rhizoctonia (and related Pythium) fungi thriving in cool, overly wet propagation media
- 2Sowing or rooting in dense, poorly draining, or non-sterile substrate
- 3Overwatering and high humidity keeping the stem base constantly saturated
- 4Crowded seedlings with poor airflow allowing rapid fungal spread
Solution Steps
- 1Remove and discard collapsed seedlings or cuttings immediately, along with the substrate immediately around them.
- 2Reduce watering sharply — allow the surface to dry and avoid waterlogging the propagation medium.
- 3Improve airflow and lower humidity around remaining seedlings to slow fungal spread.
- 4Drench remaining healthy seedlings with a suitable fungicide labelled for damping-off if losses continue.
- 5For future sowings, use fresh sterile seed-starting mix and clean, sanitised containers.
- 6Water from the bottom and avoid overhead watering to keep stem bases dry.
Prevention Tip
Damping-off is almost entirely preventable with sterile media, clean containers, and restrained watering. Sow and root in a fast-draining, sterile mix, provide gentle airflow, and never let the propagation medium stay waterlogged.
Related Issues to Explore
Propagation Failure — Cuttings Rotting or Stalling
Damping-off is one common cause of cuttings rotting — sterile media and careful moisture control address both this and general propagation losses.
Read guide
Root Rot — Pythium & Phytophthora Infection
The same wet conditions and oomycetes behind root rot also drive damping-off in young plants — both demand drier, sterile substrate.
Read guide
Southern Blight — Sclerotium rolfsii
Both attack the stem base, but southern blight strikes established plants with visible white mycelium, while damping-off targets seedlings and cuttings.
Read guide
