Green mould on your grow block
White fluff that turns bright green within a few days is almost certainly green mould (Trichoderma), the best-known contamination in mushroom growing. Eat nothing from that block, do not try to save it and throw it away straight away in a closed bag.
University of Florida / IFAS Extension · BS-01North Spore (VS), auteur Will Broussard · BP-04Trichoderma is everywhere in soil, straw and air. It takes advantage of every weak spot: substrate that was not pasteurised properly, or dirty hands and tools when inoculating.
University of Florida / IFAS Extension · BS-01GroCycle (VK) · BS-39North Spore (VS), auteur Will Broussard · BP-04How do you recognise it?
First you see white, cottony fluff that grows faster and denser than your own mycelium. After a few days it turns green from the centre, often in rings. Healthy mycelium stays white and gradually becomes denser. If in doubt, wait a few days: if it stays white, it is probably healthy; if it turns green, it is Trichoderma.
University of Florida / IFAS Extension · BS-01North Spore (VS), auteur Will Broussard · BP-04Do not confuse it with yellowing
Older, healthy mycelium can turn an even yellowish brown. That is not bright green and does not form rings.
North Spore (VS), auteur Will Broussard · BP-04What do you do?
Do not eat it. A part that looks clean does not prove the rest is safe. Keep the bag or bucket closed and remove it from your growing space. Then clean your work surface and tools with 70 % ethanol and wash your hands before you start again. Alcohol works best as a 60–90 % solution in water.
University of Florida / IFAS Extension · BS-01North Spore (VS), auteur Will Broussard · BP-04CDC (VS) · BU-08How do you prevent it?
Pasteurise or sterilise the substrate strictly according to the recipe, let it cool quickly before inoculating, work cleanly and use enough spawn. A ready-to-fruit kit has already been through that step.
University of Florida / IFAS Extension · BS-01GroCycle (VK) · BS-39North Spore (VS), auteur Will Broussard · BP-04Source
- Common Contamination in Mushroom Cultivation — North Spore (VS), auteur Will Broussard
- Grow Your Own Oyster Mushrooms at Home (SS662) — University of Florida / IFAS Extension
- What is Master's Mix + How to Make It? — GroCycle (VK)
- Chemical Disinfectants — Alcohol — CDC (VS)
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This is general growing information from the sources listed. Always follow the instructions of your kit or supplier. Only eat what demonstrably grows from your own culture of the bought, named species; if in doubt about colour, smell or shape, do not eat it.
Pick your species and your space; the tool shows what fits, with sources. No account needed.