Join Shroomok on Shroomok Buy me a coffee or Shroomok Discord or Shroomok Reddit

Black Pin Mold (Mucor and Rhizopus)

Mushroom cultivation is a kind of game of life...s

Where Grower is trying to keep proper shrooms alive & healthy, while other fungus willing to destroy them.

This page is about one of the most common and bothering contamination — Black Pin Mold

I invite you to explore main symptoms of this contamination, examine photo examples, check out prevention tips and treatment guide. Learn whether it poses any health risks to people

What is Black Pin Mold

Black Pin Mold contamination, also known as Pin Mold, Black Bread Pin Mold, or simply Bread Mold is a fungal problem commonly encountered by mushroom growers. It's primarily caused by fungal pathogens belonging to the Mucor and Rhizopus genera.

Notably, Mucor piriformis and Rhizopus stolonifer are among the most prevalent species of contaminants in mushroom cultivation.

They belong to the same taxonomic group within the fungal kingdom, sharing the Division Mucoromycota, Order Mucorales, and Family Mucoraceae.

Scientific Classification

  • Domain: Eukaryota

  • Kingdom: Fungi

  • Division: Mucoromycota

  • Order: Mucorales

  • Family: Mucoraceae

  • Genus: Mucor or Rhizopus

  • Species: i.g. Mucor piriformis and Rhizopus stolonifer (R. nigricans)

  • Mucor has approximately 40 species, while Rhizopus includes around 20 species.

    Practical distinction between Mucor and Rhizopus

    Mucor and Rhizopus are unwelcome intruders in the carefully controlled mushroom growing environment, where they compete with the desired mushroom mycelium, potentially reducing the chances for yield.

    Mucor and Rhizopus share striking visual (color and texture) and structural similarities (sporangia and sporangiophores) making it challenging to differentiate these two species based solely on disease symptoms on the eye.

    By looking at their disease symptoms Rhizopus can look like Mucor, and vice versa. Various factors such as pH level, temperature, relative humidity, and nutrients influence mold growth and its appearance. The disease symptoms of the same mold may vary if it develops under different conditions.

    For mycologists, a key difference between Mucor and Rhizopus lies in the presence or absence of rhizoids and stolons. Mucor lacks these structures, while Rhizopus possesses rhizoids and stolons.

    To confirm the identity of any contaminant, microscopic morphology is indispensable. It is impossible to accurately identify it without comparing its sporulating structures with the accompanying microscopic illustrations and/or micrographs

    But does it really matter in practice?

    Let's be honest. In practical terms for mushroom growers, the microscopic nuances between them might not be a game-changer even if you are confused whether it is Mucor or Rhizopus.

    The reason is simple. The symptoms they cause look pretty similar. More importantly, the prevention and treatment measures required to combat these contaminants remain identical. Therefore, delving into the microscopic details and differences between these molds might not be as crucial as understanding the main symptoms and how to address the issue effectively.

    Now let's shift our focus to the most common symptoms, which hold greater significance for practical use in saving your mushroom crop.

    Symptoms of Black Pin Mold contamination in mushroom growing


    Mucor mycelium typically starts with white or gray, then turns dark-gray in color.

    Made spawn to bulk a few days ago - appeared fluffy cobweb growth - contamination or mycelium?

    Rhizopus tends to be grayish, with occasional formation of a blue or yellow-colored coating on the substrate.
    Black bread pin mold on grain spawn rhizopus stolonifer

    Darker colors, resembling beads on top, often result from maturity and the formation of spores. At early stages they are white or brownish, then turn gray or black.

    Black pin mold contamination

    Texture and growth patterns

    Black pin mold mucor rhizopus contamination on mushroom cake

    • Black Pin Mold manifests as cottony to fluffy masses.

    • Mucor in its early stages is relatively tall, branched, and may have a spiky appearance often described as "cat-hair."

    • Rhizopus, in its early stages, is less tall and primarily exhibits a flat, spreading growth pattern.

    • When sporulating both molds appear as a dense mat of tall, aerial, vertically oriented hyphae upon which sit gray or black heads. Resembles a forest of black headed pins

    Mycelium Thickness

    Black Pin Mold mycelium is typically thinner than mushroom mycelium.

    Black pin mold on mushroom mycelium

    Speed of growth

    These molds are fast-growing. At room temperature, they can expand an area the size of a coin tenfold in just 24 hours.

    They can fully colonize the top layer, such as the mushroom cake or agar plate, within 48 hours after the first signs of contamination appear.

    Here is an example.

    First signs of Black Pin Mold growth:

    Early black pin mold contam on mushroom cake

    In 12 hours black pins appeared:

    Black pin mold growth

    Temperature and speed of growth

    Both Mucor and Rhizopus are thermophilic molds, thriving between temperatures of 20°C-30°C (68°F-86°F).

    Mucor can tolerate lower temperatures, ranging from 32°F-41°F (0°C-5°C), and some species can survive freezing. However, they cannot grow at temperatures exceeding 81°F-86°F (27°C-30°C), for some species like M. pusillus up to 131°F or 55°C.

    Rhizopus shows no growth below 41°F (5°C) and can grow in higher temperatures, up to 95°F-98°F (35°C-37°C).

    Sporulation patterns on Agar

    On PDA agar media, Mucor piriformis develops raised colonies and produces sporangia (gray or black pins) as they grow toward the edge of the plate.

    Rhizopus stolonifer develops mycelia that spreads throughout the media, with sporangia mainly found at the edge of the plate.


    These molds are responsible for causing soft rot in various substrates, including fruits, vegetables, plants, mushroom pins, and fruit bodies.


    While a moldy or musty odor may be present, it is not always a definitive symptom, making visual identification and understanding the growth patterns more crucial.

    How to Prevent Mucor and Rhizopus

    Mucor and Rhizopus molds can be found in various environments, including soil, plants, decaying fruits and vegetables, grains, and animal poop. Indoors, their spores may lurk in dust, ventilation and air conditioning systems, refrigerators, and can even take hold on water-damaged materials such as furniture and wooden items.

    To shield your mushroom crop from these unwelcome molds, follow these proactive measures.

    Substrate Preparation: Substrates like grain, coco coir, soil, manure, or sawdust may contain Pin Mold spores. Heat treatment at temperatures ranging from 140-160°F or 60-70°C and higher for at least one hour is an effective way to eliminate all species of molds. Proper pasteurization or sterilization ensures a contamination-free start.

    Maintain Clean Growing Conditions: Use sterilized tools and employ proper filters to protect air vents in both the fruiting chamber and spawn jars or bags, reducing the risk of airborne spores.

    Ensure that all mycological processes are as sterile as possible, and consider using a Still Air Box, Fan Filter Unit, or Laminar Flow Hood when necessary.

    Proper Ventilation: Prevent stagnant air in the fruiting chamber by maintaining a constant flow of fresh air. This can be achieved through natural air exchange or by using a fan.

    Regular Monitoring: Regularly inspect your mushroom cake to catch contamination at its earliest stage. Timely detection is key to preventing further spread.

    Regular Cleaning: Dispose of stale bread, fruits, and vegetables, as they can serve as carriers of mold spores and contribute to contamination.

    Maintain regular cleaning of your refrigerator, ventilation system, surfaces, and don't forget to clean items that hold the dust from time to time, like carpets and curtains.

    Neglecting issues in your home such as leaks, poor ventilation, and irregular cleaning can foster various types of mold growth, affecting not only your mushroom cultivation but also potentially impacting your health

    Black Pin Mold contamination treatment

    When faced with Pin Mold contamination, a straightforward treatment can be applied to inhibit its growth and increase chances for successful fruiting and harvesting. To address this issue, follow these steps:

    1. Soak a thick paper towel in 3% Hydrogen Peroxide (H2O2).

    2. Carefully lay the soaked paper towel on the area affected by the contamination to seal it.

    This treatment typically has an immediate effect: the Pin Mold mycelium dissolves, and H2O2 effectively kills mold spores. However, mold can appear again. Nevertheless, this simple and effective method helps inhibit further mold development, giving your mushrooms time to mature and be harvested.

    Additional Tip: You can make 2-3 treatments with 3% Hydrogen Peroxide, with a 12-hour break between treatments. This approach helps ensure thorough suppression of the contamination.

    Important! If you observe gray or black spores already present, refrain from using a spray bottle, as this may cause the spores to eject and spread throughout your cultivation area.

    Is Black Pin Mold toxic or safe

    Mold spores are omnipresent, both outdoors and indoors, found in soil, the air, on surfaces, plants and on various foods like bread, fruits, and veggies. Black Pin Mold, caused by some species of Mucor and Rhizopus fungi, potentially leading to diseases in plants, soft rot and undesirable in mushroom growing.

    However, they have significant roles in nature and practical applications in medicinal and industrial contexts:

    • Mucor is involved in the production of natural food colorants and is vital in biotechnology for producing enzymes and various metabolites. It's also used in the production of organic acids.

    • Rhizopus finds applications in producing organic acids, cortisone, and alcoholic beverages. In the food industry, it serves as a fermentation agent, notably for making tempeh, a traditional Indonesian food. Additionally, Rhizopus plays a crucial role as a soil decomposer in the carbon cycle.

    In general, Mucor and Rhizopus molds (including species found in mushroom cultivation) are considered safe for humans. Most species are unable to infect humans or endothermic animals because they struggle to thrive in warm environments close to 98°F or 37°C and higher. This means that a healthy immune system can effectively cope with these molds. Serious infections like zygomycosis or mucormycosis are rare and typically pose a risk to individuals with weakened immune systems.

    Anyway, it's not advisable to consume moldy mushrooms, bread, fruits and vegetables. Individuals with mold allergies should avoid handling contaminated shrooms and food, as exposure may lead to symptoms such as coughing, wheezing, runny nose, and other allergy-like reactions. Moldy products can potentially cause respiratory infections, sinusitis, and otomycosis.


    Understanding and effectively managing Black Pin Mold contamination is crucial for successful mushroom growing. By taking preventive measures, identifying symptoms early, and employing treatment in time, it is possible to save contaminated mushroom cake and get a harvest.

    Have a happy growing and healthy shrooms!

    If you find this guide helpful, please support me with cup of coffee on buymeacoffee

    Peace, Shroomok