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Category: Contams & Troubleshooting

How to identify and get rid of Cobweb Mold

Cobweb mold aka dactylium
Cobweb disease: how to identify and get rid of

Cobweb mold in mushroom growing: symptoms, prevention and treatment guide

What is cobweb mold

Cobweb is a fungal disease of commercially and home cultivated mushrooms. It isn’t just one species of mold. It is more like a closely related group of mold species.

Cobweb contamination can be caused by several related pathogens: Dactylium, Dactylium dendroides, Cladobotryum dendroides, Cladobotryum mycophilum, Hypomyces or Hypomyces Rosellus etc.

Each species of cobweb mold is so similar to its brethren that only genetic testing can tell them apart.

This mold affect magic mushrooms, edible, gourmet and wild mushrooms.

Cobweb disease on magic mushrooms, edibles and wild fungi
Cobweb mold on psilocybin, edibles and wild mushrooms

Symptoms of disease can appear on the very first steps of mushroom cultivation. For example, in spawn jars during colonization period.

Cobweb mold in spawn jar
Cobweb mold in spawn jar

During pinhead initiation and fruiting period, when pins and primordia start their active development.

Cobweb mold during pinhead initiation and fruiting period
Dactylium mold during pinhead initiation and fruiting period

❗️Cobweb spores can "sleep" in casing layer for a long time and wait for the favorable conditions to activate them. That's why cobweb most often develops in later flushes.

How to identify cobweb mold

It appears on the casing layer as small white spots. Like cottony areas. Soon cobweb envelopes mushroom mycelium, pinheads and even small fruit bodies with a soft fluffy mold mycelium that causes a soft rot.

Let's figure out main indicators of cobweb contamination.

🔴 The main symptom — cobweb mold is darker than mushroom mycelium. It has grey mycelium compared to snow-white mushroom mycelium

Gray cobweb mold contam and mycelium on grain substrate
Grayish cobweb mold contamination and white mycelium on grain substrate for spawn. Photo by So Oh - Shroomok Growers Community
Cobweb or mushroom mycelium?
Cobweb have grey color compared to snow-white mushroom mycelium

🔴 The one that sticks out is the speed of growth. Because cobweb grows extremely fast, colonizing mycelium and mushrooms on its way. A small patch, the size of a coin, grows over the entire top layer just in 1-2 day and turns into fluffy layer.

Cobweb mold in PF cake
Cobweb mold on BRF cake. Photo by adagar - Shroomok Growers Community on Discord
Cobweb mold contam
Cobweb mold disease. Photo by adagar - Shroomok Growers Community on Discord
obweb mold contamination
Cobweb mold contamination fast spreading. Photo by adagar - Shroomok Growers Community on Discord
Cobweb mold spreading on top layer
Cobweb mold spreading on top layer

🔴 Cobweb mold has very thin hyphae, while mycelium tends to be thicker ropes. Cobweb is almost transparent.

Main symptoms of cobweb mold
Cobweb mold has thin hyphae, while mycelium tends to be thicker ropes

🔴 Cobweb often appears on free uncolonized areas without mushroom mycelium.

Cobweb contamination on mushroom cake
Cobweb contam spreading (thin grey areas). Photo by varda - Shroomok Growers Community
Cobweb mold on uncolonized top layer
Cobweb disease on uncolonized bulk substrate
Dactylium or cobweb mold
Cobweb mycelium

🔴 In the later stages of disease, when molds release spores it turns red-purple and change to yellow or orange.

Cobweb disease on the late stage turns red-purple and change to yellow or orange
Cobweb mold on the late stage turns red-purple and change to yellow or orange

❗️ Such bright rich colors distinguish cobweb from another very similar mold is called mucor. Mucor has black beads at the tips when releases spores. This mold we'll figure out soon in the next article.


Cobweb Mold or Mushroom Mycelium

Color and hyphae differences of mold and mushroom mycelium are hard to identify for newbie growers haven't seen them side by side before. Your job is to know which is which. Let's figure out a few illustrative cases.

✅ Mycelium and mushroom cake looks grey, because the top layer is dry out. That's why mycelium have blue-grey color. There is no cobweb disease! Such mushroom cakes need rehydration.

Dehydrated mushroom cake, mycelium have grey color
Dehydrated mushroom cake. Mycelium have grey color, but it's not contamination
Dehydrated mushroom cake
Dehydrated mushroom cake. Mycelium have yellow-grey color, but it's not contamination

✅ Confusing bluish reaction of magic mushroom mycelium with mold. It’s not contamination!

Bluish reaction of magic mushroom mycelium
Mycelium bruises (grey-blue color)

For more examples of mushroom and mycelium bruising check out:

🔴 Recommended: Mycelium Bruises or Mold Contamination

✅ A common mistake to misidentify a weak strain of mycelium as being cobweb mold. In fact everything is good in the example below! Photo shows a healthy mycelium of different types (tomentose and rhizomorphic mix).

Different types of healthy mycelium (tomentose and rhizomorphic mix) can be confused with cobweb mold
Different colonies of healthy mycelium (fluffy thin tomentose and thick rhizomorphic mix) can be confused with cobweb mold

✅ Fuzzy feet is a symptom of lack of fresh air exchange, but it’s not a cobweb contamination.

Fuzzy feet is a symptom of lack of fresh air
Fuzzy feet = lack of oxygen. It's not a cobweb mold
Fuzzy feet is NOT contamination
Fuzzy feet is NOT contamination

🔴 Recommended: Why Mushrooms too Leggy, Fuzzy Feet and White Dots on Caps

Main causes of Cobweb Mold

⛔️ Lack of FAE (fresh air exchange). Cobweb molds enjoy stagnant air. Mushroom mycelium need fresh air. Here is one more reason why we need to ventilate our fruiting chamber. It’s not only because of the high CO2 level, it’s also because all molds like stale air.

⛔️ «Dead zones» in the monotube. As a result, insufficient fresh air exchange. Make monotube properly with correct air vents.

⛔️ Cobweb molds are favored by high relative humidity in stagnant air.

⛔️ Cobweb like combination of high relative humidity (90% and above) + high temperature (+23°C or 74°F and above) + lack of fanning (less than 3 times/day for growbox or monotube with dead areas).

⛔️ During spore-forming, cobweb is easily spread in the air and during growbox misting. Moreover, cobweb is easily spread by spores and pieces of mycelium, which stick to your clothes or tools.

⛔️ Poor sterility. Including environment, workspace, tools, bulk substrate, presence of animal hair, insects, parasites and even cultivator (hand, clothes etc) can carry mold spores.

⛔️ During sporulating phase mold easily spreads in the air when you introducing fresh air and misting growbox or monotube.

⛔️ Mushroom aborts is another common point of origin for cobweb mold. There is a clear a correlation between the development of cobweb mold and the presence aborts. However, it is hard to say that the aborts are the direct cause of cobweb disease or even if the cobweb mold was the underlying cause of the aborts.

Preventive measures of cobweb disease

Preventive measures are always the best treatment!

Sterilize or pasteurize bulk substrate, because it may contain spores of cobweb mold. In fact it's very easy to kill this mold. At a temperature of +50°C or 122°F for 30 minutes cobweb spores die. This means that cobweb can easily be prevented by proper sterilization or pasteurization.

✅ Keep all mycological manipulations as sterile as possible.

✅ Maintain favorable fruiting conditions: fresh air exchange, temperature, humidity, light. Remember, spores of cobweb mold can sleep for a long time in casing layer, but as soon as you have stagnant air in fruiting chamber mold is there.

Remove all mushroom aborts any time you are harvesting mushrooms.

Cobweb mold treatment

What to do if mold has ALREADY appeared on your mushroom cake?

The best and most common advice for treating any kind of mold is «Throw it away immediately! Avoid spreading spores in the air and on healthy mushroom cakes!»

But we have good news that give us hope!

❇️ Actually, cobweb is considered a treatable disease. It is one of the few molds which can be slowed down or even destroyed with 3% hydrogen peroxide solution (Н2О2)

🔴 Bright color is a late-stage for any kind of mold. The color indicates a sporulation process that is no longer treatable and is a huge risk of spreading contamination. It's too late for treating!

Cobweb spores
Bright color are cobweb spores. Too late for treatment!

Treatment is possible in the presence of mild contamination and only in the early mycelial stage!

Mycelial period of cobweb growth
Mycelial period of cobweb growth, NO bright color

If you want to fight with mycelial stage of cobweb you can try the following method.

  1. Spray contaminated areas of mushroom cake 3 times, 12-hour interval between treatments with hydrogen peroxide (Н2О2) solution 3%. It's ready to use solution from the pharmacy, don't dilute it!
  2. Mist not only affected area, but also healthy mycelium around contaminated spots.

    ❗️The most common reaction you see when hydrogen peroxide is introduced to casing layer is this sort of aggressive fizzing. This is directly caused by the fast conversion of the Н2О2 into its constituent parts, water and oxygen

    Cobweb mold treatment with hydrogen peroxide H2O2
    Bubbles after misting cobweb with hydrogen peroxide 3% (Н2О2)
  3. After a series of treatments cobweb mycelium should melt and disappear. If this doesn't happen dispose of contaminated cake!
    Treating cobweb disease
    Melted cobweb mycelium
  4. After treatment you should take care of the fresh air exchange in growbox/monotub. This can be: extra manual ventilation, fan/cooler or 24/7 aquarium air pump. Check if natural airflow works for your fruiting chamber.
  5. After the very first treatment reduce air temperature in growbox/monotub up to +18°..+20°C (64-68°F) for the next 2-3 days. It helps to inhibit cobweb growth.

Is hydrogen peroxide safe or harmful for mushroom mycelium

It's a common misconception that hydrogen peroxide only affects cobweb mold. In fact H2O2 kills any fungal spores (including mushroom spores) and kills mold mycelium. However H2O2 doesn't kill, but slightly inhibit mushroom mycelium growth. Don't be surprised if you get your harvest 1-2 weeks later

In case of mild contamination many pins and mushrooms may indeed live and thrive afterward!

Before cobweb treatment
Before cobweb treatment (cake 1)
Mushroom fruiting after cobweb disease treatment
Mushroom fruiting after cobweb mold treatment. 3-4 days after (cake 1)

One more example and results of Cobweb Mold treatment

Cobweb mold before treatment
Cobweb mold before treatment. Main area in red circle (cake 2)
Cobweb mold after treatment
5 days after cobweb treatment with hydrogen peroxide. Cobweb melted, mushroom cake started to fruit (cake 2)

❗️Hydrogen peroxide inhibit and kill cobweb mold, however it doesn't mean it won't come back again. Unfortunately it can be a battle till the end

As a result the most effective method of dealing with all species of mold are preventive measures and disposal contaminated cake. But don't give up if you faced with cobweb contamination!

Take advantage of a tried-and-true tip with H2O2 or salt treatment.

Salt application for cobweb mold treatment

One more effective method against Cladobotryum spp. cobweb is salt application. Most often used in commercial cultivation.

Place a damp paper tissue/towel over the growth to contain any spores that have not yet released. Then you can pour salt (refined, small fraction) over the paper towel. It helps to eliminate the cobweb mold presence in the top layer of substrate

Salt application to control Cladobotryum spp cobweb. Credit: Helen Grogan, Teagasc and Richard Gaze, WHRI & ADAS
Salt application to control Cladobotryum spp cobweb. Credit: "Identification and control of Cobweb disease on mushrooms" by Helen Grogan, Teagasc and Richard Gaze, WHRI & ADAS
  1. The patches of disease must first be gently covered with damp tissue to prevent the spores becoming airborne.
  2. Then the tissue should be covered with fine grained salt. The salt application should first seal the edges of the tissue to prevent the escape of spores.
  3. Seal the edges completely.
  4. Once the edges are sealed, more salt should be applied to completely cover the tissue and underlying patch of cobweb.

Specific control measures to prevent the spread of cobweb mold

To prevent the spread of cobweb contamination during treatment:

⛔️ Never mist growbox/monotub with untreated mushroom cake inside! Misting over untreated areas of contamination will result in a massive spore load being spread throughout the crop.

⛔️ Turn off the air conditioning or ventilation during treatment manipulations likely to disturb mold spores or pieces of mold mycelium (e.g. misting with H2O2 and salt application)

Useful stuff on Amazon to prevent or deal with cobweb disease

Basic stuff for cobweb treatment
  • Hydrogen Peroxide 3% - 32 oz $9.99
  • Ultra Fine Mist Spray Bottle - 10 oz $8.99
Sterilised bulk substrate
  • Ready Bulk Substrate - 5 Pounds - 1 Bag $32.95
Fresh air exchange and additional fanning for MonoTub
  • Quiet PC Fan with power plug cord $19.99
Fresh air exchange, additional ventilation, air filtering for GrowBox
  • Quiet Oxygen Pump for 20-100 Gallon - 2 Outlets $15.99
For sterilisation (tools, environment etc)
  • Isopropyl Alcohol 70% Spray 32 oz or bigger volume $13.95
  • Clorox Bleach Germicidal Spray 32 oz. $13.98
  • UVC Light Lamp - Ozone Free $17.99
  • UV Light Bulb with Base - Ozone, with Timer $36.99
  • Air HEPA Purifier for Home $99.99


Check out more examples of cobweb contamination in 📸 Cobweb Mold photo gallery

Join Shroomok Community on Discord and Reddit for questions and sharing experience.

You can also leave your comments on this page below ⬇️

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Have a happy growing and healthy shrooms!

Peace, Shroomok ❤️

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