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, & 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 & leafy, they are growing in an environment that is hot & 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 & 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 & 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 & fall out & 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 & Curing

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

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

Now that you know when to look for mold, let's get into how to identify & prevent cannabis molds.

Different types of mold.

Botrytis / Bud Rot

Botrytis, also known as grey mold or bud rot, is a pathogenic fungus & one of the most common fungi found on marijuana plants. Botrytis can affect the roots, stems, leaves, & buds of a plant & 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 & 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 & 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 & used immediately.
• Remove & 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 & 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 & can be easily administered through a high-silica fertilizer.

Powdery Mildew

Powdery mildew generally affects older leaves first & 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 & stems.
• As the fungus progresses it will become denser, affecting the leaves, buds, & 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 & used immediately.
• Capture & 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 & feed on plants, infecting & 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, & collapse.

Fusarium can remain dormant in the soil for years & 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 & slaked lime & 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 & Rhizopus Mold & Micro Organisms

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

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

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

Identifying Aspergillus, Penicillium & Rhizopus

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

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

Preventing Aspergillus, Penicillium & 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 & microorganisms from contaminating your plants.
• Silica gel packets - Keep moisture levels down.
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