Damping-off is a disease syndrome, not one pathogen. Seedlings either rot before they emerge, or they emerge and then collapse as the stem at the soil line turns brown, thin and water-soaked. The usual culprits are Pythium species, Rhizoctonia solani, Fusarium species and sometimes Botrytis cinerea. Fresh cuttings can suffer the same rot at the base.
In practice
The textbook sign is a seedling that looks fine in the morning and has toppled by evening, with a pinched "wire stem" at the base. Cold, waterlogged media, high humidity under domes, reused trays and unsterilised compost all raise the risk. Prevention is clean or new starter media, washed trays, warm (around 22-25 °C / 72-77 °F) but not soggy conditions, a gentle fan once seedlings are up, and no heavy feeding before true leaves. A collapsed seedling cannot be saved, so remove it and its plug to protect its neighbours.
Don't confuse with
- Cutworms: chew stems clean through at night.
- Stretching: tall, thin stems from low light, but firm and green.
- Drowning: limp but not pinched or brown at the base.
A seedling is a young cannabis plant from emergence of the cotyledons until it has several sets of true leaves, typically the first 2-3 weeks.A genus of oomycete water moulds, such as Pythium myriotylum and P. aphanidermatum, that cause brown, slimy root rot, especially in warm hydroponic systems.A soil-borne fungal disease, chiefly Fusarium oxysporum, that blocks water-conducting tissue, causing one-sided yellowing, wilting and brown streaks inside the stem.Botrytis cinerea, the fungus behind bud rot or grey mould, which rots dense colas from the inside in cool, humid conditions late in flower.Bag appeal is how good flower looks in the bag or jar, frost, colour, density and trim, which sells cannabis but does not measure its quality.Overwatering is watering so often that the medium stays saturated, starving roots of oxygen, which causes drooping, slow growth and root disease.Pest and disease prevention by changing how the crop is grown, such as humidity, airflow, spacing, watering and cultivar choice, so pests and pathogens struggle to establish.The first leaves produced by the shoot tip after the cotyledons, with the plant's characteristic serrated leaflets.Moth caterpillars of the family Noctuidae, such as the black cutworm (Agrotis ipsilon), that hide in soil by day and chew through seedling stems at night.Cleaning and disinfecting rooms, tools, containers, irrigation and people's clothing so that pests and pathogens are not carried from plant to plant or crop to crop.Decay of roots by pathogens such as Pythium, Fusarium, Rhizoctonia or Phytophthora, usually triggered by low oxygen, heat and waterlogging around the roots.
