How to Prevent Cannabis Mold?

There are many different claims about what to do with mold on cannabis plants: do you save them, toss them, or use them anyway? Before taking action, it's important to understand how dangerous certain types of molds are, and how they can negatively impact the people smoking or ingesting your product. There are three times that you're more likely to see mold on your cannabis plants:

1. During the vegetative stage
When your plants are big and leafy, they are growing in an environment that is hot and humid without much airflow. The more vegetation plants have, the more they are releasing water into the air.

The smaller a growing space is, the lower the amount of airflow will circulate. This develops pockets of stagnant air and is very common in smaller growing environments like tents.

2. During the last few weeks of flowering
In the last few weeks of flowering buds become more sensitive to mold. The larger and denser the colas are, the easier it is for them to become infected.

Mold can appear in a variety of colors. In this stage mold on cannabis is generally referred to as bud rot or Botrytis. With bud rot, the leaves around the cola will turn yellow or become loose and fall out and the bud itself will become discolored.

If you notice a visual difference in one bud but not the others, it's important to evaluate your plant immediately.

3. Drying and Curing
The methods used during the drying and curing stages will affect the appearance and quality of your bud, and can also prevent or generate mold.

It's critical to not skip any steps and to check on your cannabis regularly. If you store cannabis in jars, open the lids once a day to release toxins and let in some fresh air.

Now that you know when to look for cannabis mold, let's get into how to identify and prevent it!

Cannabis grow house.

Botrytis / Bud Rot

Botrytis, also known as grey mold or bud rot, is a pathogenic fungus and one of the most common fungi found on marijuana plants. Botrytis can affect the roots, stems, leaves, and buds of a plant and spreads fast with the ability to kill off a plant in just days.

Typically spread by wind or rainwater, Botrytis will germinate plants through an injury. If your plant has been exposed to spores, you can prevent the start of the bud rot cycle by providing a warm, dry and airy environment.

Identifying Bud Rot

• If you notice fluffy white growth in the middle or on the sides of your buds you have detected bud rot in the early infection stages.
• Botrytis is easy to detect as the color will change and the texture will become dry.

Preventing Bud Rot

• If a plant is infested move it to an outside area where you can spray it to cut down the population.
• Humidity - control humidity levels by reducing it to less than 50%.
• Propolis or bee glue - Can be purchased through online grow shops or retail stores and used immediately.
• Remove and dispose of the infected portions of your plant (create a safety margin by cutting off a bit of the healthy part).
• Ventilate the growing area by using a HEPA air filtration unit (MERV15 or higher is recommended).
• Horsetail - 1 ounce of powder makes a gallon of ready-to-spray solution.
• Essential oils - Thyme, rosemary, eucalyptus, black caraway and lemongrass can be used as diffusers to prevent bud rot from attacking your plants.
• Silica - Can be used in soil to help strengthen stems, acts as an alkaline adjustor and can be easily administered through a high-silica fertilizer.

Powdery Mildew

Powdery mildew generally affects older leaves first and may cause some to break or become distorted.

Powdery mildew is not the most dangerous fungus, but when left untreated will enter buds preventing safe intake. To stop this fungus from attacking your plants you can take the following precautions.

Identifying Powdery Mildew

• In the beginning stages of powdery mildew or PM, you may notice small circles of white dust on the tops of leaves and stems.
• As the fungus progresses it will become denser, affecting the leaves, buds, and stem by covering them in thick white mildew.

Preventing Powdery Mildew

• Horsetail - 1 ounce of powder makes a gallon of ready-to-spray solution.
• Propolis or bee glue - Can be purchased through online grow shops or retail stores and used immediately.
• Capture and remove - A self-supported, MERV15 or higher HEPA air cleaner will actively remove sub-microns preventing Powdery Mildew
• Trichoderma Harzianum - Used in the soil to effectively prevent powdery mildew


Fusarium is filamentous fungi or parasites that live within the soil and feed on plants, infecting and ultimately killing them.

Depending upon the strain of marijuana, Fusarium may cause wilt, while in others, root rot. Fusarium Root Rot will turn the roots of your plant red spreading up through the stem causing it to swell, break open, wilt, and collapse.

Fusarium can remain dormant in the soil for years and is spread through water movement or after coming into contact with garden tools. If you are dealing with a Fusarium attack, you will need to dispose of everything, including the seeds.

Identifying Fusarium

• Dark spots on the lower leaves which will quickly turn the leaves a yellowish-brown color.
• Leaves will wilt but not fall off.
• Your stems will droop.

Preventing Fusarium

• As soon as you are aware of Fusarium, you must remove the infected parts of the plant.
• If you are growing outdoors you can relocate to a new outdoor area or move your plants inside.
• Bordo Mix - An organic fungicide mix made up of copper, sulfate and slaked lime and used as a spray
• Grow room filtration systems - Ensure the cleanest grow room air with a highly effective air cleaning system. Filters recommended: MERV15 (95%) or MERV17 (HEPA)

Aspergillus, Penicillium and Rhizopus Mold and Micro Organisms

Mold and microorganisms impact both indoor and outdoor growers. They vary in color and appearance and have different effects on humans vs. animals. It's in best practice that growers learn, understand, and examine plants throughout all growing stages to protect customers and patients.

If you have identified Aspergillus, Penicillium or Rhizopus on your plants, they must be thrown away. Aspergillus, Penicillium and Rhizopus fungus spores drift into the air landing on different areas of the plant and can survive almost anything.

By implementing proper precautions early you can avoid the dangers of these microorganisms.

Identifying Aspergillus, Penicillium and Rhizopus

Aspergillus - Common mold found both indoors and outside. Generally dark green-black, Aspergillus spores create an infection in the lungs after being inhaled and can be found in soil or buds.

Penicillium - Predominantly indoor mold. Typically light blue-green spores that can ruin crops and infect and harm both humans and animals.
Rhizopus - Produces grey-black spores and may infect humans under certain conditions, such as, when a person's immune system is compromised.

Preventing Aspergillus, Penicillium and Rhizopus

• Hygrometer - Measures the humidity of the air.
• Fresh air - Ventilating your grow room with a dynamic air filtration system will establish the highest quality of air while preventing mold and microorganisms from contaminating your plants.
• Silica gel packets - Keep moisture levels down.

When it comes to mold on cannabis plants, prevention is crucial. Once mold has infected a plant, it can easily spread to other parts of the plant, including the buds, and to other plants nearby.

CleanLeaf grow room air cleaners are built to prevent mold, control odors, capture pollen, and circulate clean air throughout your growing space. Get in touch with us to learn more!

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