Powdery Mildew on Cannabis Plants

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In this guide we are going to cover powdery mildew on cannabis plants. We will explain what it looks like, and what effects it has on cannabis plants. Then we will give you some ideas for the best ways to treat powdery mildew if you find it on your plants. 

If you have powdery mildew, and you need to get rid of it fast, use the content box to skip to the treatment section of this article. Alternatively, you can start a new thread in our cannabis growers forum and ask for help there. 

So, before we move on, we should begin with what powdery mildew actually is.

What is Powdery Mildew?

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Powdery mildew is a type of fungus that affects plants. It is made up of tiny spores. These spores will land on your plant and begin to grow and spread. If they are left untreated, they can take over your whole crop.

As the mould grows it will cover the leaves of your plants. This will prevent those leaves from absorbing light, causing photosynthesis to slow down. As a result, the leaves will turn yellow and fall off the plant.  

It doesn’t take long for powdery mildew to spread. Identifying it early is key to preventing a big infection. 

What Does Powdery Mildew on Cannabis Plants Look Like?

Powdery mildew on cannabis plants will look like a white powder or dust. It will usually be found as small white patches on the leaves or stems of your plants. 

The white patches will grow and spread over time, and in bad cases the powdery mildew will cover the top and the underside of your leaves. In cases like this, it is easy to spot the powdery mildew. 

Sometimes however powdery mildew can happen later into flower. It may be harder to see powdery mildew on tip leaves that have a lot of trichomes on them. It is important to be able to recognise the difference between trichomes and powdery mildew on cannabis leaves.

Powdery Mildew Vs Trichomes

Here is a picture of powdery mildew vs trichomes. 

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Powdery Mildew Under Microscope

Very frosty buds can look mouldy at a distance, they have a white fuzz over the whole flower. It may be easy to confuse a bud covered in powdery mildew with a bud covered in trichomes. 

The best way to tell the difference between powdery mildew vs trichomes is to get a close look by using your microscope. When you look closely, you will see powdery mildew as a fine dust settling on the leaf, making the leaf white. Trichomes will stand on the leaf rather than cover it in fine dust. 

Powdery Mildew Vs Bud Rot

Here is a picture of powdery mildew vs bud rot

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Bud Rot vs Powdery Mildew

Powdery mildew will be short, curly, white strands usually found on the leaves of plants. Bud rot will have longer strands, and is more likely to be seen in buds rather than on leaves.

Bud rot will begin inside the plant and make its way outwards. Powdery mildew however will only grow on the surface of a plant. It grows best in warm humid conditions, on the surface of leaves. Because of this, powdery mildew is much easier to spot than bud rot, and it is far easier to treat.

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Powdery Mildew on Leaves

In the early stages, powdery mildew will grow on the leaves as patches of fine white powder. It spreads quickly and aims to cover the whole leaf. If you see white patches on the leaves of a cannabis plant, then it may be powdery mildew. 

Don’t panic too much though, this is easily treated. Leaves are easy to get to, and easy to clean. But things get a little more problematic if it gets on your buds.

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Powdery Mildew on Buds

Seeing powdery mildew on buds is not very common. The mould prefers to live on the leaves, but will grow on buds in bad cases. Powdery mildew likes to live on the surface of plants, so it is rare to see it grow in the inside of buds. 

Because powdery mildew lives on the surface of plants, it is easily treated and removed from the plant. If not treated however, it will spread quickly and become a problem.

Where Does Powdery Mildew Come From

Powdery mildew is a type of mould. It consists of spores. These spores are very light, and when they are hit by a breeze, they are carried off into the air. 

These spores will land on many different things, most of the time they will do nothing. But if the conditions are right, they will begin to grow. Within five days the mould spore would have completed its life cycle. During that time it would have produced thousands more spores and spread exponentially. 

Can Powdery Mildew Spread to Other Plants?

Once a mould spore has germinated, it will grow and start to produce more spores. Some of these spores will be lifted into the air and carried on the breeze. They will land somewhere, and if the conditions are right, they will begin to grow too. 

Powdery mildew can spread very quickly from plant to plant. So if you find it on a cannabis plant, you have to act quickly to prevent it spreading further. 

What Causes Powdery Mildew on Cannabis Plants

The main causes of powdery mildew on cannabis plants are warm temperatures, high humidity and bad air circulation. Mould spores are everywhere, they only germinate and spread when the conditions are right. 

As long as you keep good airflow around your plants, and control the humidity levels in the grow room, you shouldn’t see powdery mildew very often. But it is much harder to control the environment outdoors.

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Preventing Powdery Mildew on Cannabis Plants Indoors

To prevent powdery mildew on cannabis plants grown indoors there are a few things you can do. First ensure there are enough fans in your grow room. If the air is circulating well, mould spores are less likely to germinate. 

cannabis plants growing indoors, Percys grow room

Also, keep the humidity levels in the grow room below 50%. Any higher than that and mould spores may germinate. Keep fresh air moving into your grow room at all times, and make sure old air is exhausted out of and away from the grow room. 

Mould spores will germinate in warm, humid, stale air. If you don’t provide the spores with those things, they will not germinate!

Preventing Powdery Mildew on Cannabis Plants Outdoors

Preventing powdery mildew on cannabis plants outdoors is not as easy as indoors. This is because you do not have control of the environment. It can rain at any time, and humidity will rise way above the preferred 50%. 

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Instead, you have to rely on good air flow and good genetics. If you know you’re going to grow a certain plant outdoors, make sure you choose a strain that is mould resistant. But mainly, you’re best chance at prevention is good airflow. 

Make sure there is plenty of distance between your plants, and any walls or fences. This will allow fresh air to flow around them at all times

Powdery Mildew Treatment

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So let’s say you have found some white powdery patches on the leaves of your cannabis plants. You have read through this guide and you’re pretty certain that you have powdery mildew on your plants. 

Well, the good news is, it is reasonably easy to treat with ingredients you probably have at home right now. 

For some of these recipes you need to use liquid soap. Though the dish shop may work, some brands can be strong and damage your plant. It is better to use unscented castile soap if possible. You can buy that here.  

Along with the soap you will need either Milk or Baking Soda, a mister bottle, and of course, water. You will then mix one of the following recipes

Treating Powdery Mildew on Cannabis Plants with Milk

You can treat powdery mildew by using just milk and water. For example, take 1 liter of water and add 300ml of milk. Stir well so everything is mixed togher, then spray this solution on the infected parts of your plant. 

Make sure you coat the underside of the leaves too, these can often be missed. 

For best results it is recommended that you repeat this treatment once a week, for 3 weeks. If there is no sign of powdery mildew after the treatment is complete, you can stop spraying the plant. 

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Treating Powdery Mildew on Cannabis Plants with Baking Soda

Most people have baking soda in their cupboard, and it is readily available. For this mix you will also use water, and liquid soap. Dish soap is scented, and can be too strong for plants. So use castile soap if you can.

Mix 2ml of soap into one litre of water. Then add a small teaspoon of baking soda.

Stir the solution until the baking soda is dissolved and then add it to a mister bottle. Spray each leaf on your plant, on both sides. Use baking soda once a week to reduce the risk of powdery mildew.

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How to Get Powdery Mildew Off Leaves

wiping leaves of plant,

To remove powdery mildew from leaves, begin by spraying the leaves with one of the solutions mentioned above. Then, because powdery mildew is a powder, it will wipe off the leaves easily. 

This is one of the best ways to get rid of powdery mildew. Not only are you treating the mould to prevent it from growing, but you are removing spores from your plants too. 

You can also use just castile soap and water to wash the powdery mildew off the leaves. Then use the bicarbonate powdery mildew spray as a preventative once a week.

How to Get Powdery Mildew off Buds

Removing powdery mildew from buds is not as easy. The trichomes are sticky and some of the spores may stick to them. But you cant remove a lot of them with the right treatment.

You can’t wipe powdery mildew off buds the same way you can leaves. Wiping the buds will damage the trichomes, and cause more damage to the plants. 

Instead, what you need to do is wash the buds. This should be done outdoors, and away from the grow room. You will need to prepare certain items first.

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What You Need to Wash Buds

To start with, you will need 3 buckets of water, some baking soda, lemon juice and hydrogen peroxide. They should be mixed together like so:

Bucket 1

In the first bucket, you need to add baking soda to the water. For every litre of water, add 2 grams of baking soda. Stir the solution well to make sure all of the baking soda has dissolved fully into the water. That is bucket 1 complete.

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The water should be tepid. Not too warm, but not too cold. Around 15c (59f) will be fine.

Bucket 2

In bucket 2, you will add lemon juice and peroxide to the water. Peroxide (H202) will come in different strengths. Most common is 3% so we will use that as an example. But dilute your peroxide if it is stronger than 3%.

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Use 10 ml of 3% H2o2, and 2 teaspoons of lemon juice for each litre of water. This is bucket 2

Bucket 3

Just clean water. This bucket is the final rinse. It will wash any debris, baking soda, H202 or lemon juice off the buds. These things are great for washing powdery mildew off buds, but we do not want to smoke them. 

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Use the clean water to rinse the buds after washing them. Shake off excess water, and hang to dry.

When the buckets are all ready, the way you use them will depend on if the buds have been harvested yet or not.

Washing Powdery Mildew Off Buds Before Harvest

To wash powdery mildew off buds before harvest, you need to lightly spray the infected buds with the solutions from buckets 1, 2 and 3. You should spray lightly and gently wash the mildew off the buds. 

Use the baking soda solution first until the visible mildew is washed away. Then use lemon juice and peroxide solution to kill any remaining mould spores. 

Then all you have to do is rinse the bud with clean water to remove the peroxide and lemon juice, and any remaining contaminants. 

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This is much easier to do outdoors than indoors. So if possible take the plant outdoors to wash the buds before harvest. If you can’t do that, just be careful with how much you spray to reduce spillages. 

After washing, make sure the plant has plenty of airflow getting to it! The airflow will help dry the plants faster, reducing the risk of mould recurring. 

Washing Powdery Mildew off Buds After Harvest

Washing powdery mildew of buds after harvest is reasonably easy. Begin by preparing the three buckets we mentioned above. Take the bud off the plant and trim away any infected leaves around it.

Once trimmed, place the bud into bucket 1, and gently swirl it around. You’re trying to agitate the powdery mildew so it comes off the bud and into the water.

After 20-30 seconds, take the bud out of the water, shake the excess water off, and repeat the process in bucket 2, then bucket 3.

Washing cannabis buds after harvest, percys grow room,

The idea is, in bucket one, the baking soda will break up any mould and remove it from the bud. In bucket 2 the lemon juice and peroxide are antibacterial and antiseptic. This kills off any remaining spores.

Use the clean water in bucket three to rinse the buds to remove any contaminants. Then shake off any excess water and hang the buds to dry. 

Is Powdery Mildew Harmful to Humans?

Indirectly, powdery mildew will cause you no harm. But like any mould, you do not want to breathe it in. For many people it will cause no issues, but people with asthma or mould allergies it may be a problem. 

It is always best to air on the side of caution around any type of mould. The good thing about powdery mildew, is it only lives on the surface of plants, so it is easily washed off. This removes all contaminants and makes the buds safe for consumption. Just make sure you wash the bud properly! 

To Summerise!

Powdery mildew can grow anywhere if the conditions are right for it. Make sure you have good airflow around your plants, and the humidity stays below 50%. If you do find powdery mildew on cannabis plants, then don’t worry, it is easily fixed by washing it off or treating it with one of the recipes mentioned above.

If you need any help with your grow, whether it be powdery mildew, bud rot, or any other issues, we can help. Sign up to our cannabis growers forum and start a thread, someone will be along to answer your questions shortly!

Thanks for reading, I hope this post has help you get rid of the powdery mildew. If so, then please consider supporting the site on Patreon.

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