Why Mushroom Grow Bags Get Contaminated
Identify, prevent, and fix Trichoderma, cobweb mold, and bacterial blotch in your mushroom bags.
Quick Takeaway
For a quick answer, check the main steps below. Always ensure proper sanitation and optimal temperatures for the best yield.
The Enemy: Contamination
Nothing is more frustrating than waiting weeks for a bag to colonize, only to see a patch of green mold appear. Contamination happens when unwanted organisms out-compete your mushroom mycelium.
1. Trichoderma (Green Mold)
The most common enemy. It starts as bright white, dense patches (often mistaken for strong mycelium) and turns forest green as it sporulates.
Cause: Incomplete sterilization, dirty inoculation environment, or contaminated grain spawn.
2. Bacterial Wet Spot (Bacillus)
The substrate looks wet, slimy, uncolonized, and smells like sour apples or dirty socks.
Cause: Substrate was too wet. Use a hydration calculator to prevent this.
3. Cobweb Mold
A fluffy, greyish, wispy mold that grows incredibly fast over the surface of the substrate.
Cause: Poor air circulation and overly damp surface conditions.
How to Prevent Contamination
- Sterile Technique: Always wipe your hands, tools, and surfaces with 70% isopropyl alcohol.
- Proper Sterilization: Don't rush the pressure cooker. 15 PSI for 2.5 hours is mandatory for supplemented sawdust blocks.
- Check Your Spawn: If your grain spawn smells sour or has uncolonized wet grains at the bottom, do not use it.