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Writer's pictureJim Jones

Powdery Mildew on Cannabis

Updated: Oct 30

Powdery mildew, also known as white powdery mildew, comes from lots of different fungi. Powdery mildew looks like white or gray powdery growths on the leaves of your cannabis plants.

Powdery mildew on cannabis

It appears on grow areas indoors and outdoors and is foreshadowed by small bumps on the topsides of leaves. Typical species of fungi that go after hops will also go after your marijuana plants.


What is powdery mildew

Powdery mildew spores can be transported to your plants on the wind, through air ventilation systems, from pets, and any other living thing that moves (including yourself). Until the surrounding environment is ideal, the spores from mildew will stay dormant, biding their time.


What is powdery mildew cannabis

Powdery mildew on cannabis leaf

Powdery mildew is a common problem that affects cannabis plants, caused by various types of fungi. These fungi manifest as white or gray powdery-like growths on the foliage of your plants. As a cannabis grower, it’s crucial for you to identify and understand the signs of powdery mildew, as well as the steps you can take to prevent or treat this issue during your plant’s flowering stage.


Your plants may show symptoms such as discoloration, leaf deformities, and overall deterioration of health due to the presence of powdery mildew. It’s essential to be aware of the potential risks associated with this fungal infection and learn the most effective methods to eliminate it from your plants. In doing so, you’ll be better prepared to maintain a healthy environment for your cannabis plants, both indoor and outdoor, while minimizing the chances of losing your valuable crop to this persistent fungus.


What is Powdery Mildew?

Powdery mildew is a common fungal disease that affects a wide variety of plant species. It appears on the surface of leaves, stems, and flowers as a powdery, white or gray growth. This fungus reproduces through spores, which can easily be spread by the wind, air ventilation systems, pets, or humans. Once the environmental conditions become ideal, these spores can germinate and lead to a full-blown fungal infection.


Although not all plants suffer severely from powdery mildew, it can still have significant impacts on their health and productivity. When left untreated, the disease can slow down photosynthesis and potentially ruin a harvest. It is essential to regularly check your plants for any signs of this fungal growth, as catching the problem early on will help you combat it more effectively.

To safeguard your plants from powdery mildew, consider using a product such as


Bergman’s Plant Protector. This plant protection system has several benefits:

  1. Shields your plants from diseases and harmful pests

  2. Includes three 20 ml bottles, enough for up to 20 plants

  3. Compatible with soil, hydroponic, and other grow mediums

By taking preventive measures and staying vigilant, you can better protect your plants from the devastating effects of powdery mildew and ensure a healthy, productive growth.


Signs of Powdery Mildew on Cannabis

When it comes to identifying powdery mildew on cannabis, look for fuzzy, circular patches resembling flour on your plant’s leaves. Leaves may also appear spotted, mottled, and wilted. This infection rapidly spreads to nearby foliage and can cause extensive damage.

The stark white appearance of powdery mildew is easily recognizable against the green leaves. Timely and proper treatment is essential for removing it. However, dealing with powdery mildew spores can be challenging since they’re difficult to see and spread through the air.


To prevent mildew formation, ensure adequate ventilation, proper temperature, and humidity levels in your growing area. Avoid overcrowding, which can facilitate the spread of mildew between leaves. High humidity levels (above 55%) and poor air ventilation further increase the risk of powdery mildew.

Young plants are often the first target of powdery mildew, which can then spread across the entire plant, affecting stems, buds, and leaves. Infected buds will have a damp smell, and white powdery mold might be visible as well.


If left untreated, the fungus will cause the plant to turn yellow and eventually brown, ultimately leading to the plant’s death. To avoid losing your plants to powdery mildew, inspect them regularly and monitor for any unexpected changes.

In addition to cannabis, powdery mildew can affect various plants, such as roses, cucumbers, zinnias, pumpkins, trees, melons, beans, lilacs, vegetables, tomatoes, peppers, peas, phlox, and monarda.

Remember to maintain a diligent and preventive approach to cultivate healthy and high-quality marijuana plants.


How to Eliminate Powdery Mildew During Flowering

Preventing Powdery Mildew Infection

One of the best strategies for dealing with powdery mildew is to take measures to prevent it from occurring in the first place. When planting or transplanting your plants, ensure they have sufficient space between them. Close planting can increase the likelihood of powdery mildew developing.


Watering your plants at a time when they will receive at least five hours of light afterward, either natural or artificial, can help prevent powdery mildew. Indoor growers might also consider using UVC lights to protect plants from any lingering spores. Experienced growers may prune leaves that receive no direct light due to shading, reducing ideal spots for powdery mildew growth while conserving plant energy.


Addressing Powdery Mildew Spores

If powdery mildew does appear, various treatments can help eliminate it. Homemade remedies include mixing one-half teaspoon of baking soda with a quart of water and applying the solution to affected plants.

Alternatives for tackling powdery mildew include oil sprays like neem oil, sesame oil, or fish oil. A milk spray mixed in a 40% milk to 60% water ratio can also be effective due to the sun-reactive proteins in milk that form a natural antiseptic. Apply the milk spray every ten days when the plants are exposed to bright sunlight.

For infected plants, carefully remove affected leaves using a plastic bag to prevent spores from spreading. Seal the bag and dispose of it in a lidded container. Treat the remaining plant stems with a fungicide.


Other methods Cinnamon oil, garlic oil, coriander oil, clove oil, jojoba oil, and cottonseed oil sprays can be used as alternative healing methods for your plants. Copper-based applications from any garden center may also be helpful. Another option is mixing one tablespoon of hydrogen peroxide with water, which destroys the fungus through oxidation. Limonene mixed with water provides fungicidal properties without killing the fungus entirely.

Sulfur burners can be employed to control and contain the fungus, but avoid the area during treatment to prevent respiratory inflammation. Afterward, clean all windows and walls to remove sulfur residue.


Powdery Mildew Plant Symptoms

White Powdery Mildew on Leaves

  1. Pale colors

  2. White patches on leaves


Symptoms on Leaves

  1. Affected upper leaves and newer growths

  2. Impacted lower leaves and older growths

  3. Visible white powdery patches on the leaves

  4. Spots

  5. Mottled, mosaic on leaves

  6. Wilting and drooping of leaves


Symptoms on the Entire Plant

  1. Mold growth on various parts of the plant

To remove powdery mildew from infected leaves, you can try gently wiping them with a damp paper towel, taking care not to disturb the leaves too much to prevent spreading spores. To prevent future mildew growth, consider incorporating at least two fans into your growing environment: one to direct air through the plant leaves and another to expel warm air from the growing area, replacing it with fresh air.


Signs of powdery mildew weed

Signs of powdery mildew weed

Remember, plants with strong genetics are less likely to become sick and more resistant to pests and diseases, so choose high-quality seeds from a reliable source to ensure your plants’ health.


FAQ about Powdery Mildew on Cannabis

  1. Health risks: Powdery mildew interferes with your cannabis plant’s photosynthesis process, which can ultimately compromise your harvest. It’s essential to address it as soon as you notice it.

  2. Elimination from buds: Unfortunately, you cannot remove powdery mildew from buds once it has invaded. The plant will likely turn yellow, then brown, and eventually die.

  3. Treatments: Some common treatments for powdery mildew include oil sprays like neem, garlic, and sesame oil. Other options are copper-based applications and products such as Mold Control and Bergman’s Plant Protector. Additionally, sulfur burners can be useful.

  4. DIY treatments: To create a homemade spray, mix 40% milk with 60% water, or dissolve one tablespoon of hydrogen peroxide in water.


To prevent powdery mildew, consider the following factors:

  1. Climate and temperature: Favorable conditions for powdery mildew include high humidity and low light. Maintain a dry climate and sufficient sunlight to prevent its development.

  2. Watering: Avoid overhead watering, which increases the likelihood of powdery mildew.

  3. Compost and nutrients: Keep your plants healthy by providing proper nutrients through compost and appropriate fertilization.

  4. Resistant varieties: Opt for resistant cultivars if you face recurring powdery mildew issues in your growing area.

  5. Plant debris: Regularly clean up plant debris, as it can host powdery mildew spores and spread the disease.

Remember, maintaining healthy plants and providing the right care during the growing season will help in preventing powdery mildew on cannabis.


Frequently Asked Questions

What can you do to effectively treat powdery mildew on plants?

  1. Remove affected leaves and dispose of them properly

  2. Apply a fungicide that targets powdery mildew

  3. Use biological control agents such as certain fungi or bacteria

  4. Increase air circulation around plants and avoid overcrowding

  5. Limit excess moisture by avoiding overhead watering


How can you recognize powdery mildew symptoms?

  1. White or grayish powdery spots appearing on leaves, stems, or flowers

  2. Distorted or stunted growth of leaves and shoots

  3. Yellowing of leaves, followed by browning and leaf drop

  4. Infected flower buds may fail to open or bloom properly


Powdery mildew on cannabis plants 360 view

Powdery mildew on cannabis plants 360 view

What methods can help prevent powdery mildew from spreading?

  1. Regular inspection and removal of affected plant parts

  2. Create a less favorable environment for powdery mildew by maintaining good air circulation and minimizing excess moisture

  3. Plant varieties that are resistant to powdery mildew, if available

  4. Apply preventative treatments like fungicides or biological control agents early in the growing season


How can you manage powdery mildew without harming plants or the environment?

  1. Use environmentally friendly substances such as horticultural oils or baking soda mixed with water

  2. Introduce beneficial insects or microorganisms that can help control powdery mildew

  3. Implement cultural practices like proper spacing, watering, and pruning to promote plant health and avoid creating conditions favorable for powdery mildew


What is the life cycle of powdery mildew and how does it spread?

  1. Powdery mildew begins as tiny spores that land on plant surfaces and germinate under favorable conditions

  2. The fungus grows on the surface of the plant, forming a visible powdery coating

  3. The fungus produces more spores, which can spread to other plants via wind, water, or by contact

  4. The cycle continues as the new spores germinate and infect more plants


Can you save parts of plants infected with powdery mildew?

  1. It is possible to salvage plants if the infection is caught early and treated promptly

  2. Remove affected leaves or other plant parts to prevent further spread

  3. Monitor the plant’s health and apply treatments as needed until the infection is under control

  4. Maintain good cultural practices to help the plant recover and prevent future infections

You can prevent mildew by having proper ventilation and the right temperature and humidity. If you still end up with mildew, you have to treat your plants.

Powdery mildew is the most likely to occur when humidity levels are high (above 55%) when there is not much air ventilation happening in your grow area. It also occurs when there is overcrowding of your marijuana plants at the grow site or in the grow room. Leaves touching other leaves are more likely to spread powdery mildew to each other, making it even harder to eradicate when your setup looks like that.

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