Trichoderma (Green Mould)
The most common mushroom contaminant. It starts as white mycelium then turns bright green, spreads fast, and cannot be saved once established.
What it is
Trichoderma, usually called green mould, is the most common contaminant in mushroom growing. Its spores are almost everywhere in the air, and it moves fast once it takes hold on grain or substrate.
How to spot it
It starts as white mycelium that is easy to mistake for your culture, then turns a bright forest green as it sporulates, often with a sharp line where it meets the mushroom mycelium. That green colour is the alarm bell.
Prevention
Sterilise grain and rich substrate fully, pasteurise straw properly, and work in a still air box wiped with 70% isopropyl. Keep the room clean, use a vigorous culture so the mycelium colonises fast, and test any bought culture on agar before scaling it up.
What to do
There is no reliable cure once it turns green. Seal the affected jar or block in a bag and remove it without opening it near your grow, so you do not release green spores, then deep clean the area. Prevention is far more effective than any rescue.