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Insects and pests are not the only living thing that likes to feast on your cannabis plant. Mould is also an enemy of cannabis. Whether you are growing cannabis indoors or outdoors, mould can still pose a threat to your grow. Mould spreads quite quickly and can reduce yields, and can even damage your buds after harvest. There's nothing worse than going through months of time and labour, only to find you have mould growing on your plant. It is important to learn how to identify mould on your plants or cured bud and treat or remove it before it spreads and becomes a problem.

  

What is Mould?

Mould is a type of fungus, that encompasses a large group of diverse species. Similar to other fungi, mould branches out while forming a multicellular network of small filaments,  called hyphae. This forms a dense mass of fibres known as mycelium.

     

Types of Mould

There are a few different types of mould but the two main types of mould that growers experience problems with:

• White Powdery mildew
• Bud Rot

  

White Powdery Mildew (WPM)

White powdery mildew or WPM is a rapidly reproducing fungus that appears as a thin layer of white powder, almost like someone dusted flour over your plants. This pest affects both indoor and outdoor cannabis plants. To the untrained eye PM can look just like trichomes on your plant. It first appears on the leaves and if left untreated, can spread across the entire plant. 

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What Causes it?

High humidity

WPM needs moisture to thrive which means having a grow room with high humidity is all WPM needs to get started.

Low/No airflow

White powdery mildew struggles to settle down in a room where the air is being moved. High humidity will give WPM the conditions it needs to survive but poor air flow is what allows it to settle down. 

Poor ventilation

If the air in your grown room never gets exchanged for fresh air, then any spores you might have in the grow area will have multiple chances to land on your plants and reproduce. 

Leaf-on-leaf contact

Leaves that are touching each other will form moisture between them. This makes them more likely to contract white powdery mildew. Untrained bushy/leafy plants with lots of new vegetative growth are especially prone since they will often have their leaves mashed up against each other as they try to reach toward the light.

   

How to Prevent it?

Indoors

• Keep humidity levels low through proper ventilation. Having a extraction fan will help get rid of humid air in the grow room.
• Keep the air moving. A small oscillating fan moving air in the grow area will help prevent white powdery mould
• Don't overcrowd your grow room with too many plants.
• Advanced growers can defoliate some of the fan leaves that are completely shaded from the grow light to make fewer choice landing spots for White Powdery Mildew.

Outdoors

• Keep plants free of dried leaves
• Avoid planting them in areas with few hours of sunshine
• Avoid placing the plants too close to one another. It’s important that the air can circulate between them.

    

How to Treat White Powdery Mildew

The first place to start treating a bud rot problem is to check your humidity and make sure your plants have plenty of air circulation.

Early stage

If you catch the WPM in the early stage you can easily clean be cleaned off with plain water. 

If it has spread you can follow these steps:

Step 1: Remove White Powdery Mildew from leaves - You will need tap water and some paper towels. Wet the paper towels and gently wipe off as much of the mildew as possible. Be very careful not to jostle any leaves with spores on them. If there are extremely infected leaves, its best to remove them. 

Step 2: Ensure that your plants have proper airflow and ventilation - Having at least two fans in your grow room is essential. One fan should be oscillating if possible and should gently blow air over your plants. All the plants need is enough air to gently rustle their leaves which will make it hard for WPM to settle down. 

Step 3: Treat the infected plant - Mix up a treatment of your choice, we recommend trying EcoBuz Disease Pro Preventative Bio-Fungicide - 3 Doses to eliminate the mildew. This is a organic, bee& pet friendly fungicide.

As a preventative you can use Biogrow Copper Soap Organic Fungicide. This natural product acts to protect plants from infection. Therefore, it is important to have the copper soap applied on the leaves before the pathogen is able to cause an infection.

There are also some home remedies growers use such as:

• Baking soda (2 tablespoons per 4L of water)
• Neem Oil (4 teaspoons per 4L of water)

    

Botrytis (Bud Rot)

Botrytis, is also known as grey mould, but when referring to cannabis specifically, it is most often called "Bud Rot" since this is the main symptom cannabis growers are worried about with this type of mould. Botrytis often enters through openings or wounds on the cannabis plant, however healthy plants are also vulnerable. 

Bud rot will develop inside the buds and grow out if there is too much moisture trapped inside the colas. If you open up an infected buds, the inside will be mouldy dark or brown.

A cannabis plant with bud rot will show the following symptoms:

• Small black dots forming on infected structures
• Large fuzzy grey patches begin to form
• Buds and leaves begin to shrivel, turn brown and die
• Leaf tips turn from green to yellow to turn 

   

 

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What Causes it?

Bud Rot is called by the fungus known as Botrytis cinerea. Bud rot is spread to cannabis plants by dusty grey spores, usually in wind or rain water. Theses spores can easily be carried to your plant by a breeze, rain from contact with animals or even from clones. The spores can lay dormant and survive in many conditions only to affect your grow at another time.

The good news is, the fungus will never germinate if you take good care of your buds. Your plant will only be vulnerable if it is damaged by cracks in the stem from wind or over-training, damaged from pests or other fungus or has any other type of injury or weak point. 

If your plant has been exposed to the spores, it will not be able to germinate if you provide your plants with a cool, dry, breezy environment.

Here are some factors that will trigger spores to spread like wild fire.

High humidity or wetness

This is one of the most important factors if your suffering from bud rot or mould. It will keep spreading until you fix the humidity and keep the buds dry.

• Humidty that is above 55-60% is the biggest contributor to mould growth and bud rot
• Leaves should not be touching each other creating wet spots
• If buds remain wet or in humid air for several continuous hours, bud rot can be triggered 

Outdoor 

• Rainy weather can trigger bud rot
• Outdoor plants can sometimes collect dew during the night or get rained on. You should consider shaking plants to remove as much moisture as possible. 

Cool temperatures

Cool temperatures are ideal for spore germination of Botyritis. It is most common outdoors in cool, wet or rainy conditions. However, bud rot can still occur in high temperatures if the relative humidity is high. 

Warm temperatures

Warm temperatures are ideal for mould growth.  Every degree above 20°C increases your chances of mould especially in high humidity. Bud rot can strike at lower temperatures so it is recommended to aim for a medium of about 24°C during the flowering stage if bud rot is a concern. 

Bad air circulation

• Lack of wind or air circulation above and below the canopy
• Leafy plants tend to collect water between leaves and create humid pockets of air. This can create wet spots and prevent proper air circulation which creates a great environment for mould to grow. 

Dense Buds

Dense buds have a nice wet condition inside which doesn't get exposed to air. This makes them a perfect target for Botyritis. 

Sick plants

Bud rot is more likely to attack if the plant is under any kind of stress from problems like nutrient deficiencies or damage to stems.

Type of strain

Some strains are more mould resistant than others. 

    

How to Prevent Mould

Prevention is always better than cure and this is especially true when it comes to mould and cannabis. Mould can spread out of control extremely quickly if you don't notice it soon enough. 

 

Outdoors

 

Get a strain that is suitable for your climate - If mould is a concern, find a strain that is more mould resistant.

 

Breezy location - plan to place your plant in an area that gets a breeze, but not too much wind.

 

Shake plants - sometimes dew will collect on your plants during the night. If this happens it's a good idea to shake the plants to get rid of the excess moisture which is a breeding ground for spores.

 

Indoors

 

• Keep humidity under 50%.
• Create good air circulation.
• Avoid big temperature changes in your grow space. Don't let plants get too hot or too cold.
• Don't let plants sit in damp or overly humid conditions for too long.
• Remove all infected buds.
• Keep some space between buds. Creating space will allow for better airflow and reduce wet spots.
• Defoliate leafy plants. This way leaves won't be laying on top of each other, creating wet spots. Remove big leaves that are touching or covering bud sites, as well as leaves that are laying on top of each other.

 

    

How to Treat Bud Rot

If the plant is in the flowering stage, don't use fungicides or spray affected buds with neem oil. These are not affective in stopping bud rot and will give your buds a horrible taste. 

The first place to start treating a bud rot problem is to get your humidity under 50% and make sure your plants have plenty of air circulation.

• Most fungicides are not effective for bud rot. If you do choose to spary your plant, make sure it is specifically for Botrytis fungus.
• Any treatments for bud rot should be applied in the vegetative stage as a preventative.
• There is nothing you can spray on your plants after the bud rot has already formed in the buds. 

The best thing to do is control the spread and adjust your environment. The only way to stop the spread is to remove all signs of mould from the plant. Immediately remove the rotted parts an areas close by. Then keep the plant in a nice dry, cool area with a good breeze. 

When doing this be careful not to let any rot touch the rest of your plant. 

 

Some Final Note On How to Identify, Treat and Prevent Mould on your Cannabis Plant

Mould can be extremely dangerous. You need to ensure that the cannabis is safe to be consumed and enjoyed. This will not only protect your health but also the health of anyone who might be consuming your product.  

It is important to pay close attention to your plants and check them daily for any signs of mould. Keeping an eye on your plants and their environment will ensure you are not creating a perfect breeding ground for spores. 

 

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