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Mushroom Contamination: Types and Causes

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

Many worry about mushroom contamination. The occurrence is a common concern, but fortunately, there are ways to identify the problem. 

Protecting fungi from pests and other negative factors can be somewhat 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 dive in and discover all there is to know about mushroom contamination. 

Types of Shroom Contamination

Healthy fungi thrive in a hygienic environment. Even if the dish is sterile, sometimes contamination still occurs. Let’s look at the three main types of contamination in fungi below. 


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. They often cause bacteria, resulting in soft rot. 
  • Mites: While most species benefit mushrooms, some can cause harm. They feed on fungi and may cause discoloration. 

Other common mushroom pests include cecid flies, phorid flies, sciarid flies, and nematodes. The best way to avoid getting these unwanted creatures near the cultures is by keeping the environment clean. An airtight area is also an effective prevention strategy.


Where there’s moisture, mold typically flourishes. It’s also a fungus and grows through filaments called hyphae. There are several types common in mushrooms. These include: 

  • Cobweb mold: This pathogen thrives in humid conditions and doesn’t take long to affect all the mushrooms. Its color is only slightly darker than mycelium, making it difficult to detect. The cotton-like substance coats the fungi and causes soft rot. Reducing humidity and boosting air circulation may help eradicate this issue. 
  • Green mold: This pathogen is one of the most common. It’s caused by Trichoderma harzianum and produces green spores. It has an aggressive mycelium that spreads quickly and causes soft rot. The leading causes of this type of mushroom contamination are flies, unhygienic conditions, and anaerobiosis. 
  • Pink mold: This pathogen is also called bread mold or Neurospora. It’s a resilient type of mold that flourishes in numerous environments. It penetrates most materials, including cotton stoppers. If this pathogen is present, the best course of action is to destroy all infected fungi. 
  • Black mold: One of the most common grain afflictions, this pathogen flourishes on various organic substrates. Known as Aspergillus, its colors vary from black to yellow. Take caution when handling this contamination, as some varieties are poisonous. 


These microorganisms reproduce rapidly. One such mushroom contamination example is bacterial blotch. 

The affliction travels through airborne soil particles. This bacteria thrives if there’s excess water or high humidity levels. Identifying this contamination is straightforward as the mushrooms begin getting yellow and brown lesions near the edge of the caps.

Other Issues 

Mushrooms are also susceptible to sour rot, also known as wet spot. A dull gray, slimy substance forms and exudes a powerful stench. This issue is common in grain spawn jars when the endospores are heat-resistant. 

Dry bubble is another potential mushroom contamination issue. It’s a disease that leads to deformed pinheads and fungi with a tilted cap. The affliction comes from flies and dust particles. Prevention requires strict hygienic practices.

How to Tell if Mushrooms Are Contaminated 

Even if the area is sanitary, the fungi are susceptible to a variety of risks. If researchers detect the symptoms early, they may still be able to save the mushrooms.

Cobweb mold has a fluffy appearance. The strands appear rope-like and occur in splotches. Other pathogen types also display a hyphae covering that coats the mushrooms.

Bacteria are quite straightforward to identify. In many cases, the mushrooms exude a foul odor accompanied by a sludgy gray liquid. 

Noticing bugs is probably the easiest to spot. Having insects in on the fungi is an indication that the area isn’t insulated properly.

Take Action


How do microbiologists and taxonomists get rid of mushroom contamination problems? It depends on the issue. 

If the culprit is mold, it’s exceptionally challenging to save the fungi. Ideally, get rid of the culture completely. Some try retaining them by sprinkling salt on the afflicted area. 

Others opt for hydrogen peroxide as a deterrent. Spritzing the fungi with the liquid eliminates the mold without harming the mushrooms. 

If bacteria are the source of the contamination, separate the affected one from the rest. Use a sterilized spoon for the task. Either clean it with alcohol or use a flame. In many cases, the mushrooms survive. 

Pest control is tedious but doable. A little diligence can eradicate bugs from fungi before they’re damaged. Organic pesticides and neem oil application can help get the critters off the mushrooms. 

Ensuring the ideal environmental conditions also helps keep pests at bay. Factors include: 

  • Keep the area sterile. 
  • Drop the temperature while sanitation occurs.
  • Filter incoming air.
  • Insulate the room.
  • Use a blower to cause overpressure.
  • Use sticky mats and fly strips.
  • Sterilize the substrate before reusing it. 

Mushroom Contamination Cleared

Noticing mushroom contamination is 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. Keep an eye on the humidity levels, as an excess creates a breeding ground for pathogens. 

Learn more about mushrooms on our blog, which features fascinating information about these incredible fungi.

All of the 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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