Green Mold (Trichoderma)
ContaminantsAct now
Patches that start white then turn a distinct forest/lime green, usually spreading from a point; sharp musty smell.
Likely causes
- Poor sterility or handling
- Excess moisture
- Stagnant, high-CO2 air
What to do
Isolate the block and dispose of it sealed — do NOT open it indoors, the green spores spread fast. Deep-clean the area.
Easily confused with
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Sources
- Efficiency of treatments for controlling Trichoderma spp during spawning in cultivation of lignicolous mushrooms (Brazilian Journal of Microbiology (2014)). Trichoderma could not grow on non-sterilized substrates; immersion in hot water at 60 °C for 30 minutes or in alkalinized water for 36 hours were unfavourable to it; growing with the mushroom favoured it.
- Agrodok 40: Small-scale mushroom cultivation: oyster, shiitake and wood ear mushrooms (Agromisa Foundation and CTA (Peter Oei, 2005)). Green moulds are the most common contaminants at spawning, and they also grow through cracks in bags; keeping shiitake substrate dry between flushes helps because moist conditions promote contamination and attract flies; mycelial bumps on shiitake blocks are easily contaminated by green moulds.
- D.I.Y. FunGuide: Grow Your Own Oyster Mushrooms at Home (UF/IFAS EDIS SS662 (Hameed, Cotter, Liao, Hsu)). Check bags for blue, green, black or yellow spots, which indicate contamination; Trichoderma is common and shows as rapid greenish growth; heavily contaminated bags are best discarded, and partially contaminated ones may still give one flush.
Last updated: 2026-10-19