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powdery mildew on cannabis

All About Powdery Mildew on Cannabis Plants

Powdery mildew on cannabis is a common and regular problem encountered by cannabis cultivators. This white substance interferes with the plant’s capacity to photosynthesize.

If you don’t take action, powdery mildew can ruin your harvest as it spreads quickly. If it happens at the wrong time, your flowers could become unusable.

Do you want to learn more about the signs of an outbreak and how to remove powdery mildew from buds?

Let’s dive in.

What is powdery mildew?

Powdery mildew is a parasitic fungus known as white mold, oidium, or PM. A common pest in cannabis cultivation, it attacks the aerial parts of the plant.

Unchecked, powdery mildew can damage the leaves, stems, petioles, and buds, rendering them unusable. Your crop can get infected even if you use the best cannabis fertilizers.

The fungal spores are highly resilient and can lie dormant for extended periods indoors and out. They can germinate during brief spans of elevated humidity and don’t need standing water to reproduce.

There’s evidence that the effects of smoking powdery mildew may compromise human health, so it’s vital to avoid this pathogen.

Let’s delve a bit deeper into the problem.

What does powdery mildew look like?

When this problem occurs, you typically see white powder on weed or gray patches on the foliage. You may also notice bumps or small white spots on the cannabis leaves and stems. Powdery mildew often appears on top of the foliage, but the undersides can also be infected.

What does powdery mildew look like

This fungus first attacks new growth, but an extensive infection dominates mature plant matter too. It results in distortion and discoloration, causing shiny fan leaves.

Some growers get this affliction confused with mealybugs on weed. Unlike powdery mildew, these fluffy white pests suck the sap out of your plants and produce honeydew, encouraging other insects.

With mold, the infected white cannabis leaves eventually dry out and yellow, but they may also become disfigured, twisted, or broken. The disease often occurs towards the end of the growing season and can impact the buds at precisely the wrong time.

This parasite impacts the plant’s ability to photosynthesize, as it hampers light absorption. It also hinders their capacity for growth and affects general health and pest resistance properties.

Cannabis with powdery mildew is susceptible to other insects and pathogens that could kill it. Left untreated, it can damage new buds and eventually cause the plant to die.

What causes powdery mildew on cannabis?

There are several possible reasons for an outbreak. We point out the most typical triggers below.

  • Poor ventilation: Proper air circulation is crucial for avoiding powdery mildew on weed plants. The spores struggle to land and take hold in breezy grow rooms. Any enclosed space without fresh air is a prime candidate for powdery mildew infections.
  • High humidity levels: While most fungi require standing water to germinate, powdery mildew only needs high humidity. For some growers, these conditions are a problem, as immature cannabis plants also thrive with high moisture levels in the air.
  • Unfiltered airflow: Unfiltered air can carry spores that may introduce white mold on cannabis or other pests into your grow room.
  • Introducing infected clones: New additions to your grow room could be infected with this fungus. Always quarantine new clones to reduce the potential of an outbreak. 

Powdery mildew spores lay dormant until a suitable host comes along. Then, they cause white dots on your weed crops. Infections progress rapidly and become pervasive if not treated. 

Check your plants regularly to know when you may need powdery mildew treatment for cannabis. It’s best to avoid this problem altogether to reap healthy buds covered in glittering trichomes.

How to treat powdery mildew on cannabis: Step-by-step instructions

We don’t recommend smoking powdery mildew, as it may present health risks. After identifying the infection, take immediate steps to salvage your harvest. We suggest employing a combination of the following techniques:

Remove white powder from the leaves, stems, and buds

If you notice an infection, use damp paper towels to wipe the white stuff on weed off the leaves, stalks, and stems

Some growers add a little hydrogen peroxide to the wet towels. Avoid disturbing other leaves because the tiny spores can quickly spread further. 

Ensure your grow environment has good airflow

Use fans to eliminate any microclimates that may occur

Excellent air circulation is essential to reducing the potential for white mold. Use fans to eliminate any microclimates that may occur. Proper ventilation balances the environment in your grow room to produce uniform conditions and growth.

Twin oscillating fans keep the air moving around, which makes it difficult for the spores to land and take hold.

Spray your cannabis crops to kill mildew spores

You can employ several strategies to eliminate powdery mildew on marijuana plants. Growers have created various effective concoctions for spraying buds before harvest.

Here are a few of them:


Source biofungicides from gardening outlets to stop mold on weed. They trigger the crop’s natural defenses, causing it to produce a biochemical that fights off infections. 

Chemical fungicides could harm plants, animals, humans, and the environment. Always check the label before making a purchase.

Milk spray

Who knew you could use the items in your fridge to fight pathogens? Mix one part milk with three parts water and spray your plants liberally every ten days.

Sunny conditions are required for the milk proteins to activate and create an antiseptic that kills off an infection of powdery mildew on weed. 

Potassium bicarbonate or baking soda

A common preventative solution is to combine water, liquid soap, and sodium or potassium bicarbonate.

Mix a teaspoon of soap with a gallon of H2O and 1½ tablespoons of baking soda. Spray your infected plants with the solution in the mornings. Don’t do it too late, or they may burn. Repeated applications are necessary.

Some growers suggest adding 2–3 tablespoons of apple cider vinegar to a gallon of water. The 5% acetic acid can wash off and control powdery mildew on marijuana.

Neem Oil

To prevent infections, mix a tablespoon of neem oil in a gallon of water and add a few drops of liquid soap

If your crops are already infected, combine three tablespoons of neem oil with a gallon of water. Spray your plants with the mixture repeatedly to eliminate the powdery mildew problem. Never mist your flowering marijuana crops with neem oil, as it may alter their flavor and fragrance.

Trim or prune cannabis

If you discover an outbreak early, the first step is to remove infected leaves. Keep in mind that excessive shaking of the plant disturbs the spores. You could release them into the air and spread the infection.

Knowing how to prune cannabis reduces the potential for spread. When removing the leaves, be careful not to injure the plants, which could put them at risk of other diseases or pests. Treat the pinched or sliced stems and petioles with an antifungal agent. 

Put the leaves in a ziplock bag and dispose of them elsewhere. Widespread infection of white dust on weed precludes this method, as the plants won’t absorb sufficient light to photosynthesize.

How to prevent powdery mildew on weed

It’s crucial to choose cannabis seed strains that are hardy and resistant to mold or mildew. Buying marijuana seeds from our i49 seed bank guarantees excellent genetics and mold-resistant seeds.

Apart from purchasing premium strains, here are some other ways to prevent powdery mildew:

Control your humidity

Most problems with mold or mildew boil down to humidity levels. The chance of powdery mold on cannabis increases exponentially with relative humidity (RH) readings above 65% and below 40%.

Outdoor growers don’t have much recourse, but indoor farmers can use humidifiers or dehumidifiers to ensure the best humidity for pot plants. Most white mold occurs in tandem with poor air circulation.

Temperatures around 68–86⁰F are perfect for the proliferation of powdery mildew, while cannabis plants do well with air temps in the 70–80⁰F range. The fungus and the plants both flourish when there are warmer days and cooler nights.

There’s evidence that powdery mildew perishes in temperatures above 90⁰F. Unfortunately, these hot conditions aren’t conducive to marijuana growth.

How to prevent powdery mildew on weed

Ensure sufficient space between plants

Leave sufficient space between your plants to encourage airflow and limit humidity. This practice reduces the chance of microclimates that may provide the right conditions to germinate the spores, causing powdery weed.

Install air filters and UVC lights

If you’re growing cannabis indoors, it’s essential to sterilize incoming air. Use high-efficiency particulate air (HEPA) filters to eliminate the threat of spores. Although diffusion is vital, sterilization with disinfection lights may also be necessary.

Most filtration systems require regular maintenance and servicing. Simple bug screen filters are popular with greenhouse growers.

UVC lighting is a method of reducing the potential for powdery mildew on pot plants. It uses an invisible ultraviolet spectrum, producing radiation that stops spores from developing.

The light intensity and duration are crucial factors, and you may need to use this method in tandem with others.

Use an ozone generator

Ozone generators are air purification systems. They produce ozone (O3) which is highly reactive. It attaches to contaminants to oxidize and remove them. High ozone levels are required, but they may be harmful to humans and pets.

Quarantine your clones

If you buy clones, it’s crucial to quarantine them unless you want to introduce cannabis seedling problems into your grow room. They can carry spores or may already be infected with powdery mildew and could pass it on.

Frequently asked questions about powdery mildew

Although powdery mildew is a regular visitor to cannabis gardens, many growers have queries about white fuzz in homegrown weed. We answer some of the most common questions below.

How long does it take for cannabis to recover from powdery mildew?

Once you know how to get rid of powdery mildew on cannabis, you can expect the fungus to disappear within 1–2 weeks. Catching the infection early is vital. Your chances dwindle the further it spreads, but fortunately, it’s pretty noticeable. Keep a close eye on your crops.

Is it safe to smoke buds with powdery mildew?

No, it isn’t. Smoking or ingesting powdery mildew on dried buds can lead to respiratory infections, dizziness, fatigue, or brain fog. You may also experience nausea, coughing, lung irritation, or wheezing.

How do you get rid of mildew on dried buds?

There’s no cure for mold on dried weed. If you have powdery mildew on weed nugs, it’s best to destroy them. We don’t recommend smoking moldy buds.

Make sure you address the problem before you harvest. Eliminate it early in the cannabis flowering stage to reap some viable flowers.

Does bud washing help get rid of powdery mildew?

No. Bud washing involves dunking your harvested buds in buckets of water before drying them. While this technique can remove dust and some insect matter, it can’t do anything to eliminate powder mold on cannabis.


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