6 Types of Mold on Weed and How to Best Prevent Them

by | Jan 10, 2023

Written by Kristina Etter

Kristina is a digital content creator and designer. She has a talent for creating engaging and informative content that resonates with our professional audience. Kristina’s passion for the cannabis industry stems from her belief that it has the potential to revolutionize the world in many ways, and has a personal testimony of cannabis success.

Mold on weed isn’t a new problem, but commercial production and over-crowded grow rooms are creating the perfect storm for pathogens. The birth of the marijuana industry has given rise to a deeper awareness of production pitfalls and potential health risks – not from the cannabis itself, but from unintentional microbial contamination.

As cannabis cultivation stepped out of the murky shadows of the legacy illicit market, regulation, testing, and analysis prove not all commercial cannabis is created equal. In this article, we’ll review the various types of molds impacting cannabis plants and consumers and why producers should plan for increasing regulations and oversight.

Types of Mold on Weed and Other Fungi Found in Cannabis

Producers and consumers must develop a better understanding of what types of molds can infect cannabis crops and their potential impact on human health. Table 1 in this study published in Respiratory Medicine Case Reports references several pulmonary fungal infections associated with cannabis use, particularly in medical use, where the consumer was immunocompromised.

Here are a few of the most common types of mold on weed and some of the fungi impacting cannabis crops and consumers.


Fusarium is a type of fungi that is widely distributed in agricultural settings. These molds can be found in soil, plants, and crop products. Experienced cannabis producers know these molds can cause plant diseases, leading to crop losses and economic damage.

Fusarium molds can also produce mycotoxins, toxic compounds that can contaminate cannabis products and lead to health issues in consumers. Although rare, fusarium is also known to cause invasive fungal pneumonia in some cases.

Fusarium has many different species, classified by their morphology and other characteristics. Some of the most common Fusarium species found in agriculture include Fusarium graminearum, Fusarium oxysporum, Fusarium solani, Fusarium moniliforme, and Fusarium equiseti. Each species has unique characteristics and can cause different diseases in plants. Cannabis producers need to be aware of the risks associated with Fusarium and take steps to minimize their impact.

mold on weed


Pythium is a pathogenic fungus typically found in moist environments and is a common cause of root rot in cannabis. An aggressive pathogen, Pythium, can quickly spread through soil and water and can cause significant damage to indoor agriculture. Symptoms include weakened, discolored, and wilted plants, as well as root and stem rot. If left untreated, it can lead to the death of the affected plants.

Producers should regularly inspect indoor plants for signs of Pythium and take preventative measures to protect plants from this infectious pathogen. Practices such as keeping the soil moist but not overly wet and avoiding overwatering can help reduce the risk of root rot caused by Pythium.

Also, proper sanitation of tools and containers and regular removal of any dead or rotting plant matter can help reduce the likelihood of an outbreak.


Penicillium is a common mold found in cannabis cultivation. Identified as a white, fluffy, cotton-like substance, this mold appears on cannabis buds and leaves in high-humidity areas. Penicillium symptoms include discoloration, shriveling, and rot of the plant. While it is not typically dangerous to humans, the long-term health implications of inhaling it are unknown.

For producers, Penicillium can cause losses in yields and even the destruction of entire crops. To prevent it from developing inside cannabis cultivation facilities, proper humidity levels must be maintained, and specific steps should be taken to prevent moisture buildup on the plants.

Additionally, regular inspections and testing should be done to quickly identify and address any potential issues.

Powdery Mildew

Powdery mildew is a fungal infection affecting plants, resulting in a white and/or gray powdery coating on the leaves and stems. It is caused by various species of fungi and is typically more prevalent during warm, humid weather. It can cause stunted growth and even death of the affected cannabis plant if left untreated.

Although this fungus is not harmful to humans when touched or ingested, inhaling molds can lead to respiratory infections, allergic reactions, and lung diseases.

mold on weed, powdery mildew

Botrytis Cinerea

Also known as gray mold or bud rot, Botrytis cinerea is common in the humid environment of cannabis cultivation. While it can develop anywhere on the plant, it is most prevalent and harmful in the buds. The formation of dense cannabis buds creates the perfect place for humidity to condense inside the flower.

Although botrytis can be identified by its velvety, gray spores, once it is visible, it can be difficult to treat, and it releases spores to spread quickly through crowded grow rooms.

Controlling temperature and humidity levels is critical for preventing bud rot. Growers must understand how equipment and processes impact the overall environment within the facility.


Aspergillus is a fungus commonly found in soil and on plants, as well as in the air, dust, and water. Aspergillus can cause various respiratory illnesses in humans, such as allergic reactions, asthma, and fungal infections. While most people are not affected, those with weakened immune systems can be at greater risk of infection.

While aspergillus is found everywhere, for some people, inhaling aspergillus can be deadly. The chances of developing an aspergillosis infection are increased by certain risk factors, such as:

  • Taking immunosuppressive drugs
  • Low white blood cell count
  • Asthma or cystic fibrosis diagnosis
  • Corticosteroid therapy

Invasive aspergillosis can cause bleeding in the lungs, fungal growths, and even death, as it can spread to other organs such as the kidneys, heart, and brain. Unfortunately, the heat required to smoke cannabis doesn’t reach the necessary temperature to destroy the Aspergillus spores and can present an immediate danger to a consumer’s lungs.

Types of aspergillosis infections in people include:

  • Allergic bronchopulmonary aspergillosis (ABPA)
  • Allergic Aspergillus sinusitis
  • Aspergilloma (or fungus ball)
  • Chronic pulmonary aspergillosis

A review of insurance data from 2016 showed that cannabis consumers were 3.5 times more likely to develop a fungal infection than those who do not use cannabis.

Why Regulation Works to Prevent Mold on Weed

Consumers may never know what they consume without testing and reporting regulations. After The Cannabist uncovered pesticides and solvents in cannabis products, the state-mandated new testing requirements, and in 2016, they began issuing advisories and recalls for contaminated products.

Colorado recently made headlines again, as it issued two advisories within the first few days of 2023 for mold contamination. But a look at historical data shows how regulations have helped guide producers toward better production processes.

Reviewing the Colorado MED site data, it’s easy to see the decline in contaminated product incidents. After the initial reaction to the new testing in 2016, producers adjusted their processes resulting in fewer product advisories. Then, in 2022, when mold testing requirements changed, the industry saw another spike in contaminated products. As producers adjust their processes for prevention and remediation, the number of recalls should level out.

It’s also important to keep this data in perspective. According to the Colorado MED Licensee Data, the state has 1191 cultivation and 504 processing licenses. So, despite stringent testing requirements and mandates, most producers are meeting or exceeding standards.

The Future Will Be Mold-Free

As the cannabis industry continues to inch towards federal changes and more state markets adopt legal cannabis, testing requirements will only become more complex. Cannabis cultivators should consider the potential for future federal oversight and create SOPs to reduce or eliminate problems now.

Preventing Mold on Weed Before It Starts

Unfortunately, the environmental conditions in a commercial cannabis grow are naturally susceptible to molds and fungus. High-humidity environments and overcrowded grow rooms create the optimal conditions for pathogens to grow and easily spread from plant to plant.

Preventing mold on weed starts with having and enforcing standard operating procedures for cleanliness within the facility. Cross-contamination from tools, staff clothing, and personal electronic devices can introduce spores and contamination into a cannabis grow room.

Close monitoring of the conditions within the grow rooms is also critical. Cultivators may need to implement dehumidifiers to help keep humidity levels manageable. Understanding how lighting impacts humidity is also an important consideration.

Additionally, producers may implement preemptive testing procedures to find potential hot spots and identify threats. Testing solutions, like PathogenDx, can offer valuable insight for growers.

When All Else Fails, Remediate

Fortunately, in many cases, not all is lost when a product tests positive for mold. Multiple remediation technologies allow producers to salvage their harvest. Technologies such as ozone chambers and microwave decontamination can help producers eliminate certain molds, fungi, and microbials.

Some states, like Colorado, also allow producers to extract and distill cannabis if the final product tests free of contaminants.

While many of these processes are controversial, the ultimate goal is to produce a safe product for the consumer while maintaining a profit for the producer. Technologies can reduce the potential for crop loss due to contamination while maintaining the necessary standards for consumption.