Green Mold (Trichoderma) Recovery Guide: When to Save a Grow and When to Toss It

Trichoderma harzianum, commonly known as "green mold," is the nemesis of every mushroom cultivator. It is an aggressive, fast-growing fungus that actively parasitizes mushroom mycelium.

Identification

Trichoderma typically begins as a bright, dense white patch of mycelium (often whiter and more aggressive than mushroom mycelium) before sporulating and turning a distinct forest green. Once it turns green, it is releasing millions of spores into the air.

To Save or To Toss?

In Grain Jars/Bags: Toss it immediately. Do not open a green jar indoors. The grain is compromised, and opening it will contaminate your entire lab space.

In a Monotub (Fruiting Stage): If you have a fully colonized tub that is already pinning and a small patch of Trichoderma appears:

1. Quarantine: Move the tub away from your main grow area immediately. 2. Excision (The Hail Mary): Using a sterilized spoon, carefully dig out the mold and a generous margin of healthy-looking substrate around it.

3. Treatment: Spray the excised area with a 3% hydrogen peroxide solution or cover the hole in coarse salt to alter the local pH and slow the mold's spread.

Note: This will only delay the inevitable. Harvest whatever fruits mature and discard the block.

To drastically reduce Trichoderma risk, always start with high-quality, verified genetics like MYYCO liquid cultures and ensure your grain spawn is 100% colonized before spawning to bulk.

Research Citation: Seaby, D. A. (1996). Investigation of the epidemiology of green mould of mushroom (Agaricus bisporus) compost caused by Trichoderma harzianum. Plant Pathology, 45(5), 905-912.