Cannabis plant
Powdery mildew on your cannabis plants? Fear not.

If you are worried about how to get rid of powdery mildew on cannabis, you've come to the right place.

First off, if you haven't already, you should first check out our article on Preventing Powdery Mildew In Your Cannabis Garden. If you follow all our recommendations, you shouldn't ever really have to worry about powdery mildew taking hold! 

However, if you're in a location that's particularly susceptible, or you're already starting to see those tell-tale white spots on cannabis plants in your garden, you may need to ramp up your efforts to the next level.

So, let's learn how to get rid of powdery mildew with some simple, do-it-yourself recipes. Best of all, these recipes count as "organic", and should be minimally-invasive for your plants and for the environment in general.

Many of these recipes can also be used as preventative measures. In fact, you'll generally have more overall success if you implement them as preventatives! If you wait for mildew to become established, it'll be much harder to eradicate it.

#1) Beneficial Microbes!

Beneficial microbes for powdery mildew on cannabis
Beneficial microbes are your friends.

We've gone into great detail about the importance of benefical microbes in our article How To Maintain A Healthy Root Zone. If you make sure your roots are in top condition, your plants will be overall more healthy and able to fend off pathogens of all types.

And you can also put those beneficial microbe species to good use in exactly the parts of the cannabis plant that powdery mildews attacks – the leaves, stems and flowers.

A foliar feed of diluted compost tea will shield your plants with a rich, diverse ecosystem of bacteria, fungi and other microbes. This will act as a barrier preventing other, pathogenic microbes from gaining a foothold.

Although more useful as a preventative, beneficial microbes can also fight an established infection.

#2) Liquid Soap

Hand soap
Be sure to use a mild liquid soap.

Mild liquid soap, free from phosphates, chlorine and ammonia, is a surprisingly important part of an organic gardener's armory against pathogens like powdery mildew.

Liquid soap is the product of a simple "saponification" reaction between potassium hydroxide and oils such as sunflower or coconut oil. It acts as a surfactant, spreading fungicidal agents evenly over a surface. You can make your own liquid soap by following this handy tutorial.

Method: Use 0.5-1 teaspoon of organic liquid soap per one gallon of water, in combination with fungicidal agents such as sodium bicarbonate. Spray liberally over leaves and flowers a maximum of once per week, up to midway through flowering.

#3) Sodium Bicarbonate

When baking soda, an alkali of pH 9, is applied to the leaf environment, it alters the pH of from about 7 to 8. Fungi and molds generally don't tolerate alkaline pH too well, and regular application of baking soda can prevent mildew from taking hold – but again, it won't be particularly effective against a well-established infection.

Method: Mix 1.5 tablespoons of sodium bicarbonate with 1 gallon of water and liquid soap. Spray liberally up to every other day. Can also be used late into flowering.

#4) Potassium Bicarbonate

Potassium bicarbonate will also increase the pH of the leaf environment, making it another great preventative for powdery mildew on cannabis – but it actually has extra properties that make it useful as a curative too!

It's recognized as a fungicide by the EC, as it can cause "the collapse of hyphal walls and shrinkage of fungal conidia". The hyphae are the thin, branching filaments that make up the main parts of most fungi, while the conidia are the spores.

Method: Mix 1 tablespoon of potassium bicarbonate with 1 gallon of water and liquid soap. Spray liberally up to every other day. Can also be used late into flowering.

#5) Garlic

The sulfur in garlic prevents fungal spores from germinating.

Garlic is a useful tool against various common pathogens, including mildew. It contains significant quantities of sulfur, which prevents fungal spores from germinating. Garlic is useful more as a preventative than a curative.

Method: Blend 2-3 whole, unpeeled heads of garlic with a quart of water and a few drops of liquid soap. Strain through cheesecloth, blend again until completely liquefied. Spray liberally, up to 2 times per week. Can also be used late into flowering.   

#6) Neem Oil

neem oil
Use neem oil with caution, especially when disposing.

Neem oil should be used with caution, as it is less benign than other treatments on the list. It's generally safe for most mammals and birds, but may be toxic to aquatic life and bumblebees, so be careful with disposal. Use a light dilution for preventative efforts, but if fighting an infection, step up the concentration and spray more frequently.

Method: Use 1-3 tablespoons per gallon of water, plus liquid soap. Spray up to twice per week if fighting an infection, or once every fortnight for prevention. Do not use after midway through flowering.

As well as these options, if you've the tell-tale white spots on your cannabis plants, there other organic substances that can be useful in helping you get rid of powdery mildew on cannabis include copper, sulfur, hydrogen peroxide, vinegar, sesame oil, fish oil, chili, cinnamon, coriander, clove and pepper oil, among many others.

For many of these organic oils, it's the terpenes they contain that are the key to their effectiveness. You can also use just plain terpenes, such as limonene, for their fungicidal effect too!

You can blend most of the above ingredients to make your own specialized anti-mildew spray, a choice many gardeners opt for. One very popular blend is neem oil with garlic and pepper.