Mushroom Contamination: The Beginner's Guide
Houston… we have a problem. A big, green, stinky problem.
If you’ve ever tried to grow mushrooms, you’ll be painfully aware of the ‘mean green,’ a common and voracious contamination known as Trichoderma.
Picture this: you’ve spent weeks carefully colonising your grain spawn, and you’ve got your substrate ready. With giddy excitement, you spawn 5 monotubs and tuck them away somewhere safe while they colonise. You envision bumper harvests of glorious mushrooms.
After around 10 days, you decide to take a sneak peek inside to see how they’re doing. However, instead of beautiful, white mycelium, you are greeted by the shocking sight of green mould all over the surface of the substrate. The mean green has struck again.
What’s more, this tub is not the only victim. To your immense disappointment, all 5 tubs have triched out, and you’re left scratching your head wondering what on earth has just happened.
At Martian, we think this is unacceptable, and we will no longer stand by and let this happen. Enough is enough.
In this guide, we’ll go over everything you need to know about contamination, so you can finally end the nightmare and start growing more mushrooms and less mould.
What is Contamination?
Contamination is one of the most critical factors when growing mushrooms. No matter how clean and sterile your preparations and techniques are, it will, at some point, find its way into your grow bags, jars, petri dishes or tubs. It is part of the game and the only control you will have is to reduce the chance of it happening.
We can define contamination as anything unwanted in substrate or mycelium that can cause long-term problems, for example, stunt or inhibit fruiting. Contamination can spread very quickly, so it is important to get rid of the contaminated mycelium or substrate and separate it from the non-contaminated areas as soon as possible.
How to Identify Contamination?
Contaminations can be easily identified – discolouration being one of the most obvious signs. If you spot green, blue, grey, or black patches, your substrate or mycelium is most likely contaminated. However, keep in mind that blue stains on the mycelium may just be bruising and not mould, especially if the grain or substrate presses the mycelium against the glass jars and plastic bags or tubs. To determine if you have a contamination or bruised mycelium, gently wipe a Q-tip over the discolouration. Mould will colour the swab while bruising will not.
Aside from mould, slimy patches on your substrate or mycelium can also be a sign of contamination, which signifies excess moisture and the presence of bacteria.
Common Examples of Contamination
Trichoderma
Trichoderma harzianum is the most common contaminant found in mushroom growing and the easiest to identify, but one of the most difficult to contain as it grows fast. This mould is usually blue or green in colour and preys on other fungal mycelium. Trichoderma produces an aggressive white mycelium that will cover the casing and cause a soft decay in mushrooms before producing spores that are emerald green.
It can be quite difficult to spot Trichoderma in the stage of growth right before sporulation, as it may appear similar to the mushroom mycelium. However, it will have a fluffy appearance rising from the substrate while the mycelium is more rope-like and stays tight on the substrate.
Once it starts to sporulate, the best course of action is to quickly get the Trichoderma contaminated medium as far away as possible to prevent the risk of it spreading to your other grow bags, jars and tubs. Afterwards, the affected area should be sanitised thoroughly before starting another grow.
To avoid Trichoderma, there are several preventive measures you can take. The first is to make sure the substrate you’re using is not overly hydrated. Keep it at or below field capacity (68% hydration).
Secondly, make sure you’re using clean spawn. Clean your cultures on agar, and once cleaned, use a wedge of this agar to inoculate your grain spawn. Alternatively, use a clean liquid culture that you’ve tested on agar. Using spore syringes is generally not recommended, as they often contain mould spores or bacteria that can ruin your grow. However, if you must use them, make sure to also test them on agar first to ensure they’re clean enough for use. If you notice any signs of contamination on the spawn during the colonisation stage, it’s best to discard it.
When spawning your grain spawn to substrate, make sure to do it in an area that is clean and away from drafts, since if the air is dirty, there is a risk of introducing trich spores into the substrate. Also, make sure to incubate (21-27 degrees) your tubs, or grow bags, to ensure smooth and rapid colonisation. Slow colonisation can give a chance for contamination to take hold. To ensure fast colonisation, you should also use a high spawn to substrate ratio, for example, 1:1 spawn to substrate as opposed to 1:3 spawn to substrate.
Bacterial Contamination (Bacillus spp.)
The most common type of bacterial mushroom contamination is known as “wet spot” or “sour rot”. Bacterial contamination on grains is characterised by a dull grey slime with a sour smelling stench, and it makes the grains look excessively wet.
Bacterial endospores can be heat resistant. In order to prevent contamination, the grains are typically soaked for 24 hours before sterilising them to allow the endospores on the grain to germinate and be killed off during sterilisation. Without the soak, the bacteria can remain dormant and survive the sterilisation process.
Cobweb Mould
Cobweb mould looks like cobwebs and can be easily confused with mushroom mycelium by beginners because of its similar appearance, except for its colour. While mycelium is bright white, the cobweb mould is light grey.
To differentiate cobweb mould from mycelium, take a closer look at its structure. The mould is wispy compared to the rope-like hyphae of mycelium and grows three-dimensionally above the substrate. It also has a distinguishable smell of a damp basement.
Cobweb mould spreads fast. A small patch the size of a penny can cover an entire tub in a day or two. When cobweb mould comes in contact with baby mushrooms, it hinders their growth and, in some cases, may prevent them from growing at all. The mould will wrap the mushroom with its wispy mycelium, causing a soft rot.
If cobweb mould is spotted early, it can be eliminated by a hydrogen peroxide spray. This spray will not harm the mushroom mycelium but will kill any mould in your tub. This contaminant also prefers high humidity, so lowering humidity and providing more air circulation can limit its potential for contamination.
Orange Bread Mould
Orange bread mould, or Neurospora crassa, is a very common in nature and extremely fast growing. It can overtake the mushroom mycelium in a short span of time. It commonly grows through cotton stoppers and filter discs and can be very hard to eradicate.
This contaminant is bright neon orange. It has a fine orange wispy appearance at first, which will develop into a bright orange powdery patch, and if left to grow, will form orange lumpy formations.
Contaminated cultures should be carefully sealed in a plastic bag and disposed of immediately. This is to prevent it from spreading spores into the air and contaminating your other cultures. A thorough cleaning of the area that had orange bread mould nearby is also necessary.
Black Bread Mould
Also known as pin head mould, this fungus is a food decomposer and is usually the first mould to appear on stale bread. It usually grows in indoor environments and also exists in the soil and in the air. This contaminant can be carried to your mushroom fruiting blocks by gnats or fruit flies.
Black bread mould has a similar wispy appearance to cobweb mould, except for the tiny black head on the ends of the mycelium.
If you see this mould forming in your fruiting block, abandon it immediately, as it could be dangerous to people with a weakened immunity. Inhaling the spores or eating mushrooms that have grown near the mould could cause infection.
How to Prevent Mushroom Contamination
When it comes to contamination, there is one rule that every mushroom grower must know: sterile technique is king.
Sterile technique is critical for mushroom growing. Familiarising yourself with these concepts ahead of time will massively increase your chances of a successful grow.
For the inoculation phase, you want to be in a nice sanitary environment, or as clean as you can possibly find. A kitchen surface wiped down with 70% isopropyl alcohol or disinfectant is ideal. Make sure to eliminate as much draft as possible from your workspace. Although not strictly necessary, we recommend that you wear gloves and a facemask to complete the inoculation. Finally, always sanitise your hands and arms as well as the area that you are working in.
Final Thoughts
At Martian, we’ve spent years perfecting our sterile technique and substrate sterilisation process to take the headache and stress out of growing mushrooms. We hope these tips will help you achieve the same.
However, if you want to skip all the faff and leave us to worry about it, you can check out our range of grow kits or pre-sterilised substrates.