10 Common Mushroom Contaminants

The #1 enemy of mushroom cultivators. Starts as aggressive white mycelium that can be confused with target mycelium, then sporulates into vivid green.

Identification guide

Appears as grey, wispy strands hovering above the substrate. Its defining characteristic is speed — a dime-sized patch can cover an entire tub in 24–48 hours.

Identification guide

Starts white, becomes grey, then develops characteristic black-headed pins on tall aerial stalks (sporangia). Very fast growing. Common grain and straw contaminant.

Identification guide

Manifests as dull gray to mucus-like slime on grain, with a strong sour smell. On fruiting mushrooms, Pseudomonas causes yellow-to-brown superficial lesions (bacterial blotch).

Identification guide

Shows as blue-green velvety colonies with white margins, often indistinguishable from Trichoderma without microscopy. Common on under-sterilized grain.

Identification guide

A serious health hazard. A. flavus produces aflatoxins (the most potent hepatocarcinogens known). Several species cause aspergillosis ("Mushroom Worker's Lung Disease"). Handle with respiratory protection.

Identification guide

The most pernicious contaminant in mycology. Grows THROUGH cotton stoppers and filter discs. Can colonize a petri dish in 24 hours. A single sealed contaminated jar can spread spores to adjacent jars.

Identification guide

Causes distorted, stunted mushrooms with tilted caps, thickened stipes, and circular pale brown spots. Spreads via sticky spores on water splash, flies, pickers, and equipment.

Identification guide

Causes deformed, blob-like mushroom growth with amber/yellow liquid droplets. Undifferentiated tissue masses can grow as large as a grapefruit. The most important button mushroom disease in China.

Identification guide

Progresses through white → pink → cherry red → dull orange as spores mature. Slow-growing and uncommon but persistent. Colonizes compost or casing.

Identification guide