Cannabis Cultivation

What is Powdery Mildew on Cannabis: How to Fix it Fast!

Powdery Mildew Header

Powdery Mildew on cannabis is different then bud rot or mold as many growers confuse this issue. If you are looking for information about bud rot and mold, you can read more about that cannabis issue here. Powdery mildew on your cannabis doesn’t need lower humidity or even water to germinate on your cannabis buds and leaves. This makes it somewhat of a pain just because you are unable to just dial down the humidity to keep the plants from getting infected like bud rot, and mold issues.

Once it gets into your grow room it can be a real pain to control and get rid of. Lucky for most growers though, is that if you can identify it early you can rid your room of it much easier than bud rot and mold issues.

Powdery Mildew Cannabis

What Does Powdery Look Like on Cannabis Plants?

Powdery mildew starts off looking like little spots of what looks like white flour dusted on the leaves of your cannabis plants. As it gets more of a hold on your plants it will start to turn the whole cannabis leaf a white flour like color and look. Once it completely takes over the plant and leaves it will slowly start to kill the plant until the plant is no longer alive. Growers will notice that the plant leaves will slowly start to turn yellow as the plant slowly gets more infected. 

It typically starts off in very small spots on the plant and can appear anywhere on the plant even though it is mostly concentrated on the leaves of the plant. It can however show up on the stems, buds. Normally it will only infect the top of the leaves although it can start on the underside of the leaves in some cases. 

Powdery Mildew on Cannabis Plants

How does Mildew Spread from Plant to Plant?

Mildew spores actually spread from cannabis plant to plant though the wind outdoors on mild warm days, and they spread the best when the weather is dry. They do not spread near as well in wet, cool weather. It can also be spread, by pets, humans, or tools that have been used or have brushed up against your plants.

How to prevent Powdery Mildew From Spreading?

Powdery Mildew can live on plants and buds and many other things in the grow room. For this reason it is very important to keep all your tools clean. It is also extremely important to remove any affected plant material from the grow space to prevent spreading. It can live on plant material for some time dormant, then once conditions are right it will start to spread again. 

When removing leaves be careful as the spores can stick to your fingers and hands, then every plant you touch after touching the infected plant will spread the sporse to other plants. Only touch and work on the infected plant. Then wash your hands well with soap and water before moving work to new plants. This is the same for indoor plants as well as outdoor plants. 

New outbreaks can come in from old infected vegetation that was left in the grow room. 

Never defoliate a cannabis crop that has been infected with powdery mildew, first you will be spreading the spores as well as there will be far less foliage. This means that it will have less areas on the plant to infect, and kill the plant much faster. 

If your rooms are connected by ventilation you will want to make sure that the air flow is shut off until you can fix the problem in any room that is connected to the infected room. 

Growers can also choose a powdery mildew resistant strain for growing. Different strains can also have varying amounts of resistance to the mildew check with the cannabis seed breeder if they offer strains that will be more resistant. 

Giving your plant enough space in the grow room can also be a help to prevent spreading. When plants are close together it is much easier for the spores to jump around from plant to plant and it all creates an environment that is harder to see.

White Powdery Mildew Treatments

There are a few different treatments, to rid yourself of this, depending on how advants the mildew is, and how much it has infected the plant. The good news is that if it is caught early it can be treated without doing damage to the plant. It will most likely slow the plant down in its growth stage. With the right treatment you can correct the infection. 

You may have to spray the soil for mildew, this type of mildew can live in the soil and will be able to stay dormant in the soil.

How to Get Rid of Powdery Mildew?

Two ways exist to get rid of powdery mildew. The first is homemade prevention, and the second is using a commercial fungicide. Both of these ways have their pros and their cons when it comes to using them on your cannabis plants. Some can be used only in the vegetative stage while not in the flowering stage of growth. 

Some of these ways below involve changing the PH of the leaves of the cannabis plant in order to create an environment that is not suitable for the mildew spores to germinate on the plant. 

All these methods should be used liberally on the plant, mildew likes to send out its spores over the garden looking for a happy place to start growing and thriving. Any missed spots will be new breeding grounds for the spores to thrive.

Powdery Mildew Cannabis

Baking Soda Powdery Mildew on Cannabis

Mix in a spray bottle 1 tablespoon of baking soda, and a few drops of liquid dish soap. This will work for up to a gallon of water or a few liters. We would recommend this be sprayed on the plants as a preventative as it will work best this way. Mix this up well in the spray bottle and use it on the entire plant. It is safe to spray it on all parts of the plant and will help keep spores for germinating and growing.

Powdery Mildew Using Vinegar

Our second way to prevent powdery mildew and change the PH of the plant‘s outer layer is to use vinegar. This is another great preventative, to use in your growing room. You can use about 2 to 3 tablespoons of regular white vinegar or apple cider vinegar as well this will help keep the spores from once again germinating on your plants. This method is safe to use in vegetative growth and flowering. It will not harm your plants as well and you can spray every few days if you are prone to issues with powdery mildew.

Making a Powdery Mildew Spray for Cannabis

Growers can also use vinegar, and baking soda to make a very effective spray for cannabis plants. Just be sure to mix this in good with the water so it will not clog up the spray nozzle. Make sure to spray the plants every week, the leaves, stems and top of the soil. This spray helps to create a PH on the plant that the spores are unable to grow on. Prevention is the best way to keep mildew out of your growing space.

How to Get Rid of Powdery Mildew in Soil?

Once again instead of making a spray you can, mix up some baking soda and vinegar to use as a great soil drench for your cannabis soils. Once you have mixed up these three things very well, next time that the soil needs a good watering, you can use this mix in place of a normal straight watering. Do this once a month and it will keep powdery mildew out of your cannabis soils.

Can Growers Reuse Soils with Powdery Mildew in it?

If you know your soil contains powdery mildew then like with the plant itself we recommend that you dispose of it after the garden has finished up. Never use this soil in another garden or anywhere else if you have a flower garden in your yard you can use it for something like that. If you have mildew on your plants, it is highly likely that you have it in the soil as well, so it is best to move on and get new soil. 

If you are on a budget, you can after harvest break up the soil and place it in turkey trays. Then place the trays full of soil into the oven and cook the soil until it reaches 275 F. Make sure to check the inter soil for the correct temperatures. Heating the soil to this temperature will kill the mildew spores in your soil. Remember this will also kill anything else in the soil, good or bad. You can then reuse this soil for your garden once again.

How to Use an Over the Counter, Fungicide for Treatment

There are lots of over the counter fungicides that you can use to treat powdery mildew as well. Growers have two types of fungicides that work well for cannabis treatments. The first is sulfur, as the name suggests these are made up of sulfur that can be mixed with water and used to treat mildew issues on cannabis. Another fungicide that can be used on cannabis is copper-based products. This will work great for breakouts to get them stopped before spreading. However we do not recommend using this during the flowering period of the plant. Use this as a preventive during vegetative growth can also help to prevent getting mildew during flowering.

Powdery Mildew on Cannabis Clones

It is rare to see powdery mildew on cannabis clones, as the environment for clones is somewhat different then in your typical growing rooms. However if you do get it on your clones this can be a good sign that it is as well living on the mother plants that they were taken from. If this is the case you may want to use one of the recommendations above on the clone as well as the mother plants.

Powdery Mildew Cannabis Plants

Powdery Mildew During Flowering

This is one of the more common times that mildew will attack your cannabis plants. Your beautiful green buds will start to look white with powdery. When this happens you will not be able to just dial down the humidity and kill it like mold. It will need to be treated with one of the natural treatments above. We recommend that you not use a Fungicide as smoking is a bad idea. There are treatments that you can use, but they should be stopped two weeks before harvesting.

Powdery Mildew Late Flower

Sadly if you end up with Powdery Mildew in late flowering it is going to be pretty much impossible to stop at that point. You may want to cut your losses, and just harvest at this point. The worst of this is that even harvesting will be moving millions if not billions of spores throughout the growing space. However you can wash your buds as we discuss in this article. 

Powdery Mildew on Cannabis at Harvest

If you had mildew in late flower there is a pretty good chance that it will be alive and well in your harvested cannabis buds. If you don’t want to toss the crop you can give it a bath per say. You can take your harvested fresh buds and give them a bath in lemon juice and hydrogen peroxide solution to try and clean the buds of the mildew and spores. If you use this method be sure to clean them very, very well. 

Take the large flowering cannabis colas from the plants, and use a bucket with water, hydrogen peroxide and lemon juice to wash the colas (Main flowering buds) from top to bottom. Be careful not to miss any spots on the plants, and get into the infected buds well. You want to make sure you get every last bit of the mildew.

Once this is completed, it is advised to cure and store your buds for a few weeks, you will know if the mildew has been fully removed if it does not spread in the jars after curing. If you do see it then the buds should be destroyed. (and not by smoking them)

Is Powdery Mildew Harmful To Humans

It is not harmful to humans to touch or eat this type of mildew. It can cause allergic reactions in certain people. Never smoke, or vape buds that you know have mildew on them, it is never a good idea to inhale mildew, mold spores so you should destroy them.

When Should you Scrap The Plant and Cut Losses

If you can’t stop the powdery mildew it is best to just destroy the crop and cut your losses. Once your plants start to turn yellow and slowly die, your plant may be best to just cut them down and move on. If your plants are still pretty healthy and green try some of the methods above and see if you can fight it back before resorting to killing the plants. This is especially true if you are further along in flowering and would like to do anything possible to keep them.

Cleaning Your Growing Space

Once you have had an outbreak of mildew it is very important to clean your room, tools and anything else that comes into contact with the space or the room. Using ISO alcohol to clean everything will kill the spores in the space. Make sure to clean everything very well as the spores can get into corners in the space or your tools.

How Do You Remove Powdery Mildew from Buds?

Cleaning your infected plants with hydrogen peroxide can remove powdery mildew from your buds. Make sure to clean them well if you are going to go this route with your harvested cannabis buds.

Final Thoughts

While annoying this plant infection can be fixed and you can even clean your buds if it does get to that point. As with anything cannabis growing, keep a close watch everyday on the plants. If you recognize any of the symptoms of Powdery Mildew, act quickly to get it under control and keep using the techniques in this article to keep it away and never come back!  

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