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How to Deal with Powdery Mildew on Cannabis

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Cannabis powdery mildew might have a nice ring to it, but it is one of the worst things that can happen to your weed grow. Though it is a catastrophe to have at any time, it strikes worst when you are starting to harvest. The very action of harvesting ensures the spores are spread, and once they land on your buds there’s is not much that can be done to save them.

Luckily, it doesn’t have to be such a sad story, and although it is damaging on vegetating crops, the effects are not as drastic as those on buds. Let’s discuss what powdery mildew on cannabis is, its effect, and what can be done to prevent and manage it.

What is Powdery Mildew?

Powdery mildew is kind of fungal disease which presents as a white or gray powder that is generated by the spores of the fungi. It first attacks the cannabis leaves before migrating to the rest of the marijuana plant including the buds. Just before you see the powder, you might spot tiny blisters on the leaves upper surface. The powdery mildew spores are most often spread through the air in the growing areas. To a less extent, they can be spread by human handling, tools, and even animals that brush against affected plants.

Powder mold is likely to thrive in areas of high humidity and moderate to cool temperatures. It also spreads very fast in crowded grow areas. It majorly attacks the young leaves of mature plants. This means that younger plants are also at a higher risk of infestation. From the leaves, the mildew quickly spreads to the rest of the plant. When your cannabis starts smelling of rotten vegetation, it is terminally infected. Once infected to this degree, the best cause of action is to remove and bag all infected plants, being careful not to infect healthy ones.

How do you Identify White Powdery Mildew?

Plants are infected for long periods of time, even weeks before you see the first symptoms. This makes it very stealthy and gives it the opportunity to spread without notice. You will know that your cannabis plants have white powdery mildew if you spot the following on them:


White Spots on Cannabis Leaves

When your cannabis leaves are infected, you will see the following symptoms:

  • Pale colors on the leaves
  • Transformation of the cannabis leaves from a vibrant green to a pale yellow.
  • White patches on the leaves
  • Upper leaves and any newer plant growth is affected
  • Fuzzy, white circular patches of powder which look like flour appearing prominently on the leaves
  • Spots
  • Mottled, mosaic appearing on leaves
  • The leaves wilting and drooping
  • Mold on the plants

White Powdery Mildew on Cannabis Buds

  • Grayish-white coating- This can easily be confused for trichomes, or the other way around, so be careful.
  • White or gray powdery appearance.
  • Distinct odor that is mildewy or smells like hay.


What Will White Powdery Mildew do to Your Weed Plants?

White powdery mildew on cannabis plants can have several catastrophic effects, some of which are:

Eat your Cannabis Plants: Though white powdery mildew usually starts on the leaves, it quickly spreads to the rest of the plants and quickly “eats it up”, cutting off all the plants processes and causing what’s left to begin to rot.

Multiply and Spread Across your Marijuana Plants: Powdery mildew on cannabis plants also multiplies and spreads at a prolific rate. It can go through a whole crop in a matter of days, which could mean that the grower could lose all his plants.

What Causes Powdery Mildew on Cannabis?

Several factors contribute to the development of powdery mildew on you weed plants. The main factors are:

High Humidity

An environment with high humidity is ripe for the thriving of cannabis mildew. This poses quite a problem because young cannabis plants also do well in relatively humid conditions of 40%-60% RH. Luckily, high humidity only poses a threat when it is paired with lack of proper airflow, which we will discuss next.

Little to no airflow

If the air in a grow room is constantly moving, powder mold will have a hard time settling and establishing itself on your cannabis plants. Stagnant air combined with high humidity gives WPM the perfect environment to establish itself and thrive. A fan, even a small oscillating one can go a long way in ensuring the air is constantly moving, and therefore eliminating a majority of WPM woes.

Poor Ventilation

A closed, unventilated space is ideal for WPM to thrive in. You should ensure that your grow room is well ventilated and stale air constantly gets exchanged for fresh air to discourage spores from settling.

Too much contact between leaves

When leaves touch each other, they are likely to form moisture between them that could easily lead to WPM. Untrained leafy or bushy plants that have lots of new growth are also very prone to WPM, with the added disadvantage of meshing together as they strain to find light.

Defoliating can go a long way in ensuring less incidence of WPM, as well increasing the energy available for the plant to grow its buds, therefore increasing yields!

How to get Rid of Powdery Mildew on Cannabis

There are very many effective powdery mildew cannabis treatment methods. We will however discuss our most favorites in killing powdery mildew on cannabis:

Anti-Fungal Sprays

Because powdery mildew on weed is a fungal infection, fungal sprays are particularly effective in eliminating them. This however needs to be done in the earlier stages, and care needs to be taken not to contaminate the cannabis buds.


Spacing your plants by moving them from crowded spaces to giving them more space can go a long way in reducing the chances of your cannabis getting infected by WPM.

Foliar Sprays   

Foliar sprays are not as concentrated as usual fertilizers and most use natural materials such as kelp, compost, herbal tea, and fish emulsion. Spraying foliar can halt the growth of WPM as it acts as a natural antiseptic. While spraying, please ensure to spray the bottom of the leaves and rest of the plant as well.

Cutting off Infected Areas

This is as straightforward as it sounds. Simply cut off the infected areas being careful not to shake off any spores and bag immediately for disposable. You can combine this method with spraying to ensure that any leftover spores do not establish themselves.

How can you remove powdery mildew from infected buds?

Unfortunately, once buds have been infected, it is not possible to remove the fungus. When the buds of a marijuana plant have been infected, you will notice it turning yellow, then brown just before it dies.

It is therefore very important to prevent bud rot from infecting our cannabis plants.

How to Prevent Powdery Mildew from Appearing

 Maximize Air Circulation 

As we have mentioned above, still air is the stuff WPM uses to thrive. Having the air in your grow room circulate will go a long way in ensuring that WPM does not get a chance to settle and start multiplying. Just two fans can go a long way in achieving this. One fan can oscillate and if possible blow air over your plants as the gentle rustling of the leaves will discourage PM from settling on your cannabis plants. The second fan in the other hand should be in your grow room but pointing outwards to enable the exchange of hot air with fresh air. The placing of the second fan to face outwards will force humid air out of the room, in turn pulling in new air. This fresh new air can them get circulated in the room by the first oscillating fan.

Remember, two fans is the bare minimum.

Prune Plants Regularly 

Regularly pruning plants will ensure that the leave are spaced out, therefore reducing the chances of WPM thriving. Pruning also ensures that you are in close contact with your cannabis plants and therefore you will be able to pick out any anomalies and the establishment of WPM in its early stages.

Regulate and Control Humidity 

As mentioned, humidity is a big factor in the establishment of White Powdery Mildew on cannabis. Ensuring hot humid air is let out, and fresh new cool air comes in will greatly reduce your chances of WPM. You can use a hygrometer to ensure that the humidity in your grow room is at the most ideal, and take measures to adjust it where need be by the use of fans as described above or other humidity control measures.

Maintain Air Purity

Purifying air might be a concept that is foreign but trust me, it does exist. Apart from getting fresh air to exchange with the old air in your grow room, you can get an air purification system to literally “scrub the air” in your grow room clean. An effective air sanitation system completely keeps the air free of mold spores, and any other blights which will go a long way in ensuring your cannabis grow does not get affected by powdery mildew.

These state-of-the-art devices draw in fresh air and “sanitize” it before releasing it into the grow room. Any old, fungi, spores or any other airborne particles get destroyed before the air is introduced into the grow area.

Maintaining the purity of your air will ensure that you never have to deal with white powdery mildew.

Stop Cannabis Powdery Mildew Before it Becomes a Problem

Powdery mildew on marijuana plants is without doubt one of the most serious adverse cannabis plant conditions. Luckily, if arrested on time, it is easy to fix and the plants can continue to thrive. In the fight against White Powdery mold, prevention is indeed better than cure.

Ensure to apply the preventive methods we have outlined, and if your plants happen to get infested, use the treatments discussed to stop the mildew from progressing further.

The importance of early spotting and fast action cannot be over emphasized. Early action ensures that the powdery mildew does not spread, putting your whole crop into jeopardy. Happy, powdery mildew free growing!

Powdery Mildew Q&A

What is powdery mildew?

Powdery Mildew is a type of fungus that rapidly reproduces, both sexually and asexually and leads to the eventual death of the plant it has infected. Fortunately powdery mildew is easy to spot in your cannabis plants because of the white patches it forms while growing that stand out like a sore thumb against the cannabis plants’ green leaves. If spotted early, it can be removed from plants, or the infected plants can be disposed of to prevent any further spreading.

How do you prevent powdery mildew?

As we have mentioned, the most effective way of dealing with powdery mold is stopping it even before it begins. Some other effective ways of preventing powdery mold are:

  • Buy Strong Seeds- Seed with strong genes will be better able to fend off the fungus.
  • Allow for Plenty of Grow Space- As discussed, powdery mildew thrives in confined and crowded spaces. While transplanting, ensure to provide adequate space between plants.
  • Optimize Fans- Placing fans in your indoor marijuana garden will help regulate the airflow thus preventing the growth of mold. As we have outlined, using two fans to directly blow into the leaves, and dispel used air while bringing in new air will eliminate the chances of powdery mildew settling to reproduce on your cannabis plants.
  • Use of Plastic Bags to Dispose of Infected Leaves-To ensure the powdery mildew does not spread, the infected plants and pieces should be carefully placed in plastic papers and disposed of responsibly.
  • Use Sprays- Commercial products such as Mold Control offer alternatives to help plants repel powdery mildew. More natural alternatives are garlic, cinnamon, clove, jojoba, cottonseed, and coriander. These natural remedies also help in healing the infected plants.
  • Other unconventional Methods- A tablespoon of hydrogen peroxide mixed with water and applied to the leaves eradicates powdery mildew by oxidizing the cells of the fungus. A teaspoon of limonene diluted in a quart of water will also effectively kill the powdery mildew fungus.


Sebastian is a passionate advocate of CBD's therapeutic potential, dedicating himself to exploring its diverse benefits. As a seasoned writer, he eloquently shares his insights and personal experiences with CBD, aiming to educate readers about its transformative power. His life's mission is promoting holistic wellness, with CBD at the heart of his advocacy.