How To Identify A Contaminated Mushroom Culture

Contaminated Magic Mushrooms

There is a wide palette of contaminations lurking out there. Most of them can be separated into three groups: Bacteria, mould (fungi) and pests. Let's take a closer look at the most common types.

Cultivating mushrooms at home isn't the easiest of tasks. It isn’t exactly rocket science, but one needs to be careful and extremely clean, as conditions should be kept sterile at all times. Every part of the mushroom culture is very vulnerable to contamination, including the spores, the mycelium and the mushrooms themselves.

Substrate sterilization and air filtration are ways of keeping the environment sterile and rich for the mycelium, but free of competitors such as bacteria, mould or pests. However, these methods aren’t foolproof. The mentioned processes aren’t perfect and the sterile environment has a limited duration in practice.

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We can say, that a contamination is anything unwanted in your substrate or mycelium, but mainly being impurities in the air, soil or water, that can cause long-term problems with your mushroom culture. Spore contamination can prove to be fatal to the whole culture, while contamination during the fruiting phase can lead to cap removal.

Contaminations can spread very quickly, so it is best advised to get rid of the contaminated cultures and move them from the non-contaminated ones. On the bright side, contaminations are easily identified, as the mushroom mycelium is completely white.

If you see any other colours, you can expect to have a contaminated culture. But don’t be too hasty, as there are two exceptions. One is the colour blue, which indicates bruising on the mycelium, while the other is the colour yellow, which is an indicator of the mycelium getting old and producing new defences against bacteria.

Different Kinds of Contaminations

Contaminants will flourish in the sterilized substrate used for cultivating mushrooms, as they have no competition there like in nature. When mushrooms grow in the wild, the complex relationship between arrays of bacteria, fungi and such maintain an ecological equilibrium in which the mushrooms grow freely, without the need to fight with contaminants over substrate dominance.

As you see, there is a wide palette of contaminations lurking out there. Most of them can be separated into three groups: Bacteria, mould (fungi) and pests.

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Bacteria are unicellular microorganisms, that reproduce very fast and they can be dealt with pasteurization and sterilization of the substrate. Mold is a fungus, that grows in the form of filaments called hyphae and can be controlled with salt, baking soda, alcohol, cinnamon, etc.

And last but not least, are the pests, tiny insects, that devour your culture and transmit diseases, that affect it. Pests can be controlled with strict sanitation and an airtight grow room.


Now that we have established the different types of contaminations in your mushroom culture and how to identify them, we will cover the most common examples.


Magic Mushrooms Wet Spot / Sour Rot

A common occurrence in grain spawn jars, the bacillus sometimes survives sterilization in the shape of endospores resistant to heat. When the medium is contaminated with bacillus, a dull gray slime is formed, that reeks with a foul stench and makes the grain look excessively wet, hence the name.

If you want to eliminate endospores from your grain you should soak it at room temperature for around a day. This way the endospores will germinate and be viable for sterilization.


magic mushrooms Bacterial Blotch

If you notice yellow to brown lesions at or near the edge of your mushroom caps, then bacterial blotch has contaminated your culture. The bacteria spreads by airborne soil particles and it occurs if your mushrooms stay wet 4 to 6 or more hours after they have been watered. It is controlled by lowering humidity and applying a 150ppm chlorine solution.


magic mushrooms Cobweb Mold / Dactylium Mildew

When a cottony mycelium covers your casing and envelops your mushrooms upon contact in a soft mycelium, which causes soft rot, then your culture is contaminated with cobweb mould. This mould is a little bit darker than mycelium and this slight difference in colour could go unnoticed by a beginner.

Another telltale sign is the great speed of growth, as cobweb mould will cover the whole casing in a day or two, starting from a dime-sized patch. High humidity favours this contaminant, so lowering humidity or increasing air circulation helps the problem.


magic mushrooms Green Mold

It is caused by Trichoderma harzianum and distinguished by an aggressive and white mycelium that will cover the whole casing and mushrooms, causing soft rot and producing spores, that are emerald green. Green mould is currently the most widespread disease in the US Agaricus industry.

Poor sanitation, flies, anaerobiosis and more influence the occurrence of green mould, making strict sanitation essential and the use of surface disinfectants farm-wide.


magic mushrooms Pink Mold / Red Bread Mold

Also called Neurospora, it is a fast-growing fungus commonly found in agar and grain. Present everywhere in nature, this contaminant grows through cotton stoppers and filter discs and is very hard to eliminate. Contaminated cultures should be destroyed immediately and a thorough cleaning of the laboratory is necessary.


magic mushrooms Blue-Green Molds

These fungi are very common on speciality mushrooms, whose spores are airborne and ubiquitous. Blue-green spores are produced on the surface of the substrate. These fungi are one of the greatest concerns in agar and grain cultures.


magic mushrooms Black Mold (Also Yellow Mold And Others)

These fungi are very common in agar and grain cultures, as they are found on almost any organic substrate. Called Aspergillus, it prefers a near neutral to slightly basic pH and species range in colour from black to yellow. Some of these species are toxic and produce deadly aflatoxins, so they should be handled with special care.


magic mushrooms Dry Bubble

A disease caused by the Verticillium species of fungi, which produce sticky spores. Symptoms of the disease vary with stage of development. Early infection leads to the production of deformed pinheads and infection at a later stage leads to a crooked mushroom with a tilted cap.

As the spores are sticky, they spread via dust particles and one should be careful of moving soil near mushroom houses. Other methods of control are the prevention of flies entering the aforementioned mushroom houses and putting table salt on top of tissue paper which should contain the disease.


magic mushrooms Fungus Gnats

Tiny, flying insects, that are attracted to the mushroom crop. They feed on the mycelium and tunnel into the mushrooms. Tissues, that have been damaged by the gnats are often overrun with bacteria, which cause soft rot.

Adults are 0.3cm long, grayish to black flies, whose wings are clear with no pattern and few distinct veins. Strict sanitation and general hygiene are the way to go concerning control of these contaminants.


magic mushrooms Mites

Small arthropods commonly found in straw and manure. Most species of mites are beneficial to mushroom growing, as they feed on eelworms and other mites and are actively engaged in the fragmentation and mixing of the organic substrate.

However, there are few, that can cause damage. They feed on the mushroom mycelium like the fungus gnats and may cause surface discolouration. Detailed sanitation and hygiene are key in controlling these contaminants, as any other.

This covers the most common contaminations you can come across in mushroom cultivation. If something is to be learned here, then it is, that a clean environment and careful handling go a long way.

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