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Detailed Treatment for Powdery Mildew on Cannabis

Cannabis growers often encounter powdery mildew, a fungal disease affecting the plants’ quality and yield. The fungus spreads quickly and, if left untreated, can cause the plant to die and lead to economic losses.

Powdery mildew on cannabis is a common problem but can be challenging to control and requires quick action to prevent the disease from spreading. If this is the case, you must take various steps to treat powdery mildew and prevent it from becoming problematic.

This article will introduce and explain all there is to know about cannabis powdery mildew in an indoor grow room by outlining what powdery mildew is and how to identify it. The article will then explore the causes and symptoms of powdery mildew. Finally, at the end of the article, we will outline the steps you can take to treat powdery mildew on cannabis and prevent it in the future.

We provide a content table below for quick and easy navigation throughout the article.

What is Cannabis Powdery Mildew

Powdery mildew is a parasitic fungus that is also known as white mold and Oidium, it is commonly referred to as 'PM' by cannabis growers. This fungal disease is highly contagious and can quickly spread from plant to plant through airborne spores.

The parasitic nature of powdery mildew requires live tissue for growth and reproduction. As a result, the fungus attacks the aerial sections of cannabis plants, including the leaves, stems, and buds. If left untreated, powdery mildew will keep damaging the whole plant.

Powdery mildew spores can stay inactive for a long, making future cannabis plants vulnerable to the disease if not treated. Therefore, it's crucial to take action and eliminate the problem.

How to Identify Powdery Mildew

Powdery mildew can potentially affect cannabis plants at any growth stage, although most typically young plants contract the disease. This may be because young plants require high humidity levels to grow properly, creating the environmental conditions that lead to powdery mildew spreading.

Therefore, identifying powdery mildew on cannabis plants is critical to preventing and treating the disease.

Here are some key features to look for when identifying powdery mildew:

  • Powdery Substance:The most common symptom of powdery mildew is a white or gray powdery substance that appears on the plant's leaves, stems, and buds.
  • Distorted Growth:Powdery mildew can cause the leaves to twist, curl, or deform.
  • Yellowing Leaves:Infected leaves may begin to turn yellow or brown as the disease progresses.
  • Weak Stems:Powdery mildew weakens the plant's stems, making them more susceptible to breaking.

Powdery Mildew On Cannabis Plants

Powdery mildew fungus can affect different parts of the cannabis plant. Leaves, stems, and buds are commonly affected. The severity of the infection determines the coverage areas and patterns.

Here is a 360°panoramic view of cannabis infected with powdery mildew:


Powdery Mildew on Leaves

When powdery mildew affects a plant, the foliage will look like it has white or silvery powder sprinkled on the affected areas. It may start as small spots or patches and gradually spread and merge.

Infected leaves may also become deformed, curl, or twist and turn yellow or brown as the disease progresses. In severe cases, powdery mildew can cover the leaves top and underside.


Powdery Mildew on Stems

This powder may resemble flour and usually forms on the upper surface of leaves, although it does sometimes form on stems and flowering buds. Infected stems can become weak and break easily, it can significantly reduce the yield and quality of the flowers.

Powdery Mildew on Flower

At the same time, powdery mildew on flower buds can cause buds to become misshapen and stop growing, which can significantly reduce the yield and quality of the flowers. In severe cases, the fungus can cover the entire surface of the buds, making them unsuitable for use.


Powdery Mildew on Dried Buds

Powdery mildew on dried buds is a significant concern for cannabis growers and users, as it can render them unusable. The fungus appears as a white or gray powdery substance on the surface of the dried buds, which can be easily identified.

Infected dried buds with powdery mildew may have a musty or moldy smell and a strange taste. Therefore, it is essential to identify and remove any buds affected by powdery mildew to prevent the further spread of the disease.


Identify Cannabis Powdery Mildew and Other Diseases

Powdery Mildew VS Trichomes

In severe cases of powdery mildew, the white substance can cover the leaves top and underside, making it easy to spot the disease. Powdery mildew may appear later in the flowering stage, making it hard to differentiate it from trichomes. So, it's crucial to identify the difference between the two to take prompt action.


Powdery Mildew VS Bud Rot

Powdery mildew and bud rot are two distinct types of fungal diseases. The main difference between them is their location and symptoms.

Powdery mildew looks like a white or gray powdery substance on the plant's surface, including the leaves and buds.


Where does Powdery Mildew Come From

Powdery mildew is a fungal disease that produces lightweight spores. The spores can easily spread through the air or water. When the spores land on a plant, they can germinate and grow quickly, penetrating the surface to extract nutrients from the host.

Can Powdery Mildew Spread

The answer is "Yes." Powdery mildew can spread quickly from infected plants to healthy ones. The fungus produces tiny spores that can be carried by the wind, water, or other means, allowing it to spread rapidly from plant to plant. These spores can also survive on surfaces such as soil or plant debris, making it easy for them to persist and infect new plants.

As it spreads, it will cause the leaves to curl upwards before eventually killing the plant. Further, if left untreated powdery mildew can devastate an entire indoor grow room rapidly. Importantly, PM has a window of time after inoculation (approx. 4 - 7 days) where it remains invisible to the naked eye.

Disease Cycle for Powdery Mildew

The life cycle of powdery mildew can vary depending on the species of the fungus and the environmental conditions. However, in general, the life cycle of powdery mildew follows a pattern involving spores' production, their dissemination, germination, and infection of the host plant.

The life cycle of powdery mildew typically starts with the production of asexual spores on the surface of infected plant tissues. These spores are dispersed by wind or water, and they can land on new host plants.

Germinated spores produce tube-like structures called hyphae. The hyphae penetrate the plant's surface. They extract nutrients for growth and reproduction.

As the fungus grows, it produces new spores, which are released into the air and can infect other plants.

The life cycle of powdery mildew can be completed within a few days or weeks. It depends on the environmental conditions and the virulence of the fungus.

What causes Powdery Mildew on Cannabis

High humidity: High humidity and warm temperatures create an environment that is favorable for powdery mildew to grow and spread.

Poor air circulation: Poor air circulation in growing areas can cause stagnant air, leading to high humidity levels and making it easy for the fungus to spread.

Low light levels: Powdery mildew can also develop in areas with low light levels because the fungus prefers to grow in cool and shaded environments.

Overcrowding of plants: When plants are crowded together, it makes it easy for powdery mildew to spread from infected plants to healthy ones, leading to an outbreak.

Environmental stress: Stressful growing conditions can weaken the plant's natural defense mechanisms. These conditions include extreme temperature fluctuations, drought, and nutrient deficiencies. Weak plants are more susceptible to powdery mildew.

Use of contaminated tools or equipment: Contaminated equipment or tools can easily spread fungal spores. This can lead to an outbreak of powdery mildew.

How Does Marijuana Get Powdery Mildew

Powdery mildew can easily grow and spread when temperatures are between 60-80°F (15-27°C), and the relative humidity is high.

Powdery mildew requires a relative humidity of around 40-70% to grow, although higher levels can be even more conducive to its growth. When the humidity level is high, powdery mildew spores can germinate quickly, and the fungal colonies can spread to nearby plants. So, controlling humidity levels is important to prevent powdery mildew growth and spread.

What Are the Health Risks of Powdery Mildew on Cannabis

Powdery mildew on cannabis plants can lead to reduced growth, yield, and potency. It can also potentially spread other diseases. Consuming cannabis infected with powdery mildew can lead to lung infections and respiratory problems. The fungus can also produce harmful toxins. Therefore, taking prompt action to prevent and control powdery mildew is essential.

How to Prevent Marijuana Powdery Mildew


Step 1: Control humidity levels

To prevent powdery mildew from developing on your cannabis crop, the humidity levels in your grow room should be kept under control. Powdery mildew thrives in high-humidity environments. So, maintaining proper humidity levels can prevent the growth and spread of the fungus.

HVAC equipment with dehumidifiers can help in controlling humidity levels indoors. However, when choosing a dehumidifier, certain factors must be considered. For example, a larger grow room with more plants would require a larger dehumidifier.

Step 2: Maintain proper ventilation

Good air circulation and flow are crucial to preventing the growth and spread of powdery mildew. When air is circulated properly, excess moisture is constantly removed from the environment, and any airborne particles, microbes, and fungi do not get to settle down.

Using fans, open windows, or using HVAC equipment can improve ventilation indoors.

Step 3: Manage Your Plants

You can prevent powdery mildew from becoming a problem by managing the plants in your grow room properly.

This includes ensuring that the room is not too crowded, even at maximum capacity. Moreover, making sure that none of the plants are in contact with one another will lower water retention and help prevent powdery mildew. Further, ensure that you do not overwater your plants, as this will have the same effect.

Step 4: Keep your grow area clean

Sanitizing your grow area before and after growing can help prevent the spread of powdery mildew.

Step 5: Use high-quality soil and plant food

Providing your cannabis plants with high-quality soil and plant food can help boost their immune system and make them more resistant to powdery mildew.

Incorporating these measures can help prevent powdery mildew from occurring in your indoor grow space. In addition, using HVAC equipment with dehumidifiers can help control humidity levels and improve ventilation, making it an effective tool for preventing powdery mildew.


Preventing powdery mildew in outdoor cannabis plants can be more challenging than indoor plants, as growers have less control over environmental conditions. Weather changes, such as sudden rain, can lead to increased humidity levels, creating the perfect conditions for powdery mildew growth. As a result, growers must rely on other methods to prevent powdery mildew from developing.

One effective method for outdoor powdery mildew prevention is choosing cannabis strains that are resistant to mold. By selecting the right genetics, growers can significantly reduce the risk of powdery mildew development in their outdoor crops.

To achieve good airflow, it is essential to space outdoor cannabis plants appropriately. Growers should maintain adequate distance between plants and walls or fences to promote proper air circulation. This can reduce humidity levels around the plants, preventing the growth and spread of powdery mildew.

How to Treat Powdery Mildew

Can Plants Recover from Powdery Mildew

Plants can recover from powdery mildew if the disease is detected early and appropriate measures are taken to treat and prevent its further spread. However, recovery time and success depend on the severity of the powdery mildew infection and the stage at which it was detected.

How Long Does It Take to Recover

The time it takes for a plant to recover from powdery mildew depends on the infection's severity and the treatment's effectiveness. With prompt and effective treatment, recovery can occur within a few weeks. However, recovery may take longer in severe cases, and the plant may suffer from reduced growth or yield.

How to Treat Powdery Mildew on Cannabis Indoors

Here are some indoor measures to treat cannabis powdery mildew that can be integrated with HVAC equipment:

1.Adjust temperature and humidity levels:

Powdery mildew thrives in high humidity and temperatures, so it's crucial to maintain proper environmental conditions to prevent its growth. This can be achieved by integrating HVAC equipment that can regulate temperature and humidity levels to a range suitable for cannabis growth.

2.Increase airflow: Good air circulation is essential in preventing powdery mildew growth. HVAC equipment such as fans can be used to improve air circulation, thereby reducing the risk of powdery mildew growth.

3.Use UV-C lights: UV-C lights can be integrated into HVAC equipment to prevent the growth of powdery mildew. These lights emit ultraviolet radiation, which can destroy powdery mildew spores and prevent their further spread.

4.Apply fungicides or natural remedies: Fungicides or natural remedies such as neem oil or sulfur-based products can be used to treat powdery mildew.

5.Using a grow room HVAC system: These can be applied using an HVAC system, such as a misting system that delivers the treatment directly to the plants. By integrating these measures with HVAC equipment, growers can effectively treat and prevent the growth of powdery mildew in their indoor cannabis crops.

Treating Powdery Mildew on Cannabis Outdoors

To treat cannabis powdery mildew, similar measures can be taken both indoors and outdoors. These measures include removing infected plant material, maintaining proper ventilation, controlling humidity levels, and using natural remedies.

While some of the measures used to treat cannabis powdery mildew are similar for both indoor and outdoor settings, there are also some key differences. For example, in an indoor setting, HVAC systems can be used to control humidity levels, while outdoors, this may be more difficult to achieve. Additionally, outdoor growers may need to rely more heavily on natural remedies, as chemical fungicides may be more difficult to apply and can pose environmental risks. Finally, outdoor growers may also need to take additional steps to protect plants from weather events, such as rain or strong winds, that can facilitate the spread of powdery mildew.

More Advice for Treating Powdery Mildew on Cannabis Plants

How to Get Rid of Powdery Mildew on Leaves

One of the best ways to remove powdery mildew from cannabis leaves is by spraying them with a solution of fungicides or natural remedies, such as neem oil or sulfur-based products. After spraying, the powdery mildew can be easily wiped off the leaves, as it is a powder that doesn't stick to the plant. This method not only treats the disease but also removes spores from the plants, reducing the risk of further infections.

Another effective method for removing powdery mildew is washing the leaves with a solution of castile soap and water. This method can help to remove the powdery mildew without the use of chemicals, making it an excellent option for those who prefer natural remedies. After washing, growers can use a preventative measure such as a bicarbonate powdery mildew spray once a week to reduce the risk of further infections.

How to Get Powdery Mildew off Buds

Getting powdery mildew off buds can be challenging as buds are delicate and prone to damage. In most cases, it's not recommended to attempt to remove powdery mildew from buds as the process can damage or contaminate them. It's best to focus on preventing powdery mildew from developing in the first place.

If powdery mildew does develop on buds, it's crucial to act quickly to prevent the disease from spreading. One method is to carefully trim off any visibly infected areas and dispose of them properly. Growers can also use a solution of water and hydrogen peroxide to wash the buds carefully, ensuring that they are thoroughly dried before storing them.

However, it's important to note that in severe cases, it may not be possible to save infected buds, and it's better to dispose of them to prevent further contamination of the plant.


How to Get Rid of Powdery Mildew on Cannabis During Flowering

Getting rid of powdery mildew on cannabis during flowering can be challenging as plants are more delicate during this stage. The first step is to identify and remove any infected plant parts to prevent the disease from spreading. This includes removing any leaves or stems that have visible signs of powdery mildew, such as white powdery patches.

Once the infected plant parts have been removed, growers can implement a treatment plan to control and prevent the disease's further spread. Treatment options include the use of fungicides or natural remedies, such as neem oil or sulfur-based products. However, it's important to note that some treatments may not be suitable fo flowering stage, as they can affect the taste and aroma of the plant.


1.Is powdery mildew harmful to humans?

Powdery mildew is a fungal disease that affects plants and does not generally cause harm to humans. The spores of powdery mildew are not known to cause any significant health issues in humans, although they can cause allergic reactions in some people, such as sneezing, runny nose, and itchy eyes. However, it's important to note that while powdery mildew itself may not be harmful to humans, the use of some fungicides to control it can be harmful if not used properly. It's always important to follow the instructions on any pesticide or fungicide product carefully and to take the necessary precautions to avoid exposure, such as wearing gloves and a mask.

2.Should I cut off powdery mildew leaves?

To prevent the spread of powdery mildew, it is important to cut off any leaves that are visibly affected. Use clean tools and cut the affected leaf off at the base of the stem, as close to the main stem of the plant as possible. Dispose of the leaves carefully by placing them in a plastic bag and disposing of them in the trash. It's also important to take preventative measures, such as maintaining good air circulation, monitoring humidity levels, and using fungicides when necessary. By taking action early, you can help protect your plants from the damaging effects of powdery mildew.

3.How does powdery mildew spread on cannabis?

Powdery mildew spreads through spores in the air and can rapidly proliferate in conditions of high humidity, poor ventilation, or insufficient light.

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