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Comprehensive Guide to Managing Common Mushroom Contaminants

Plates of agar inoculated to observed interactions between Trichoderma sp. and Sclerotium rolfsii

Many worry about mushroom contamination. This common concern can be addressed by learning to identify the problem early. Protecting fungi from pests and other negative factors can be challenging, but it becomes easier once you know what to look for. Detecting infestations or afflictions early is the best way to prevent them from spreading to the rest of the fungi. Let’s explore everything you need to know about mushroom contamination.

Types of Shroom Contamination

Healthy fungi thrive in a hygienic environment. Even in a sterile dish, contamination can still occur. Below are the three main types of contamination in fungi.


As with any form of gardening, pests are a concern when working with mushrooms. Bugs can consume and infect fungi. Common insects that pose a threat and result in mushroom contamination include:

  • Fungus gnats: These pests consume mycelium and can damage the tissue of the mushroom, often causing bacteria, resulting in soft rot.
  • Mites: While most species benefit mushrooms, some can cause harm by feeding on fungi and causing discoloration.

Other common mushroom pests include cecid flies, phorid flies, sciarid flies, and nematodes. Keeping the environment clean and airtight is the best way to prevent these unwanted creatures from contaminating cultures.


Where there’s moisture, mold typically flourishes. It’s also a fungus and grows through filaments called hyphae. Common molds in mushrooms include:

  • Cobweb mold: Thrives in humid conditions and can quickly affect all the mushrooms. Its slightly darker color than mycelium makes it difficult to detect. It causes a cotton-like substance to coat the fungi, leading to soft rot.
  • Green mold: One of the most common molds caused by Trichoderma harzianum, producing green spores. It spreads quickly and causes soft rot, often introduced by flies, unhygienic conditions, and anaerobiosis.
  • Pink mold: Also known as bread mold or Neurospora, it’s resilient and flourishes in many environments, penetrating most materials, including cotton stoppers. Destroy all infected fungi if this pathogen is present.
  • Black mold: Common in grain afflictions, known as Aspergillus, it flourishes on various organic substrates and varies in color from black to yellow. Handle with caution as some varieties are poisonous.


These microorganisms reproduce rapidly, with bacterial blotch being a notable example. This affliction travels through airborne soil particles and thrives in excess water or high humidity. It is easily identifiable by the yellow and brown lesions near the edge of the mushroom caps.

Other Issues 

Mushrooms are also susceptible to other afflictions, such as sour rot (wet spot), characterized by a dull gray, slimy substance with a powerful stench. Common in grain spawn jars when the endospores are heat-resistant, this issue requires strict hygiene. Another issue is dry bubble, a disease leading to deformed pinheads and tilted caps caused by flies and dust particles.

How to Tell if Mushrooms Are Contaminated 

Even in sanitary environments, fungi are susceptible to various risks. Early detection of symptoms can save the mushrooms.

  • Cobweb mold: Appears fluffy with rope-like strands in splotches.
  • Bacteria: Often identified by a foul odor and sludgy gray liquid.
  • Bugs: Easy to spot, indicating that the area isn’t properly insulated.

Take Action Against Mushroom Contamination


How do microbiologists and taxonomists address mushroom contamination problems? The method depends on the issue.

  • Mold: Often challenging to save affected fungi; ideally, remove the culture completely. Some attempt to salvage it by sprinkling salt on the afflicted area or using hydrogen peroxide to eliminate mold without harming the mushrooms.
  • Bacteria: Separate the affected mushroom from the rest using a sterilized spoon, cleaned with alcohol or a flame. In many cases, the mushrooms can survive.
  • Pests: Diligence can eradicate bugs before they cause damage. Organic pesticides and neem oil can help remove pests. Maintaining ideal environmental conditions, such as keeping the area sterile, lowering the temperature during sanitation, filtering incoming air, insulating the room, using blowers to create overpressure, sticky mats, and fly strips, and sterilizing the substrate before reuse, are effective strategies.

Mushroom Contamination Cleared

Noticing mushroom contamination can be disheartening. In some cases, the fungi are beyond help, but most of the time, solutions can remedy the issue. Prevention is the best option and requires a clean, bug-free environment with plenty of airflow. Monitor humidity levels, as excess moisture creates a breeding ground for pathogens. Learn more about mushrooms on our blog, featuring fascinating information about these incredible fungi.

All content and images on our site are for informational reference only. The cultivation of psilocybin mushrooms is federally illegal in the United States. We do not promote the cultivation of psilocybin “magic” mushrooms under any circumstances. Do not contact us asking for advice related to this subject. Any products found on this site are for microscopy and taxonomy purposes only. None of the psilocybin mushroom spores we offer are for consumption or cultivation. We do not sell any products containing psilocybin.


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