Written by Joshua Sosin

Powdery mildew is a cannabis grower's nightmare. This white, powdery fungus can spread quickly and ruin an otherwise healthy cannabis crop. That's why pro-growers are always prepared to address the issue and treat it like a plant health crisis.

In this guide, we’ll break down the causes of powdery mildew and what expert growers do when plants get infected.

Want to learn more about how experts grow cannabis? Check out the Mood Blog.

Table of Contents

• What Is Powdery Mildew?

• What Causes Powdery Mildew on Cannabis?

• How Growers Identify Powdery Mildew

• How Dangerous Is Powdery Mildew?

• Preventing Powdery Mildew on Cannabis

• Treating an Active Powdery Mildew Infection

• Can You Still Use Cannabis Affected by Powdery Mildew?

• Final Thoughts

What Is Powdery Mildew?

Powdery mildew is a fungal disease that affects many plants, including cannabis.

This mildew shows up as white or grayish powdery spots on the leaves, stems, and buds of the plant. The fungus thrives in environments with high humidity, poor airflow, and fluctuating temperatures.

Unlike other fungal infections, powdery mildew doesn’t need standing water to spread. Instead, its spores travel through the air and attach to cannabis plants, making it a persistent and challenging issue for growers.

What Causes Powdery Mildew on Cannabis?

Quite a few environmental factors contribute to powdery mildew outbreaks. Here are the main issues that can lead to mildew growth:

• High Humidity: Powdery mildew thrives in environments with humidity levels between 55% and 75%.

• Poor Air Circulation: Stagnant air creates the perfect breeding ground for spores.

• Temperature Fluctuations: Warm days and cool nights encourage spore development.

• Overcrowded Plants: Dense foliage blocks airflow and traps moisture, creating an ideal environment for mildew.

• Contaminated Equipment: Spores can transfer from infected plants, tools, or clothing.

• Weak Plants: Plants that are stressed due to overwatering, nutrient deficiencies, or pest infestations are more vulnerable.

How Growers Identify Powdery Mildew

Expert cannabis growers know how to identify powdery mildew so that they can address it as fast as possible. Here are some of the signs they look for:

• White, powdery spots on leaves, stems, and buds.

• Yellowing or wilting leaves, often mistaken for nutrient deficiencies.

• A musty odor as the infection spreads.

• Curling or distorted leaves.

• Buds covered in a white, dusty coating.

How Dangerous Is Powdery Mildew?

Powdery mildew is more than just an eyesore. It can be a serious threat to a cannabis grower's crops. If left untreated, it can:

• Weaken the plant’s immune system, making it more susceptible to other diseases.

• Reduce yields by interfering with photosynthesis.

• Destroy buds, making them unsafe to consume.

This is why growers work hard to take preventative and curative measures against powdery mildew. Here's what that process looks like.

Powdery Mildew Prevention: How Growers Treat Powdery Mildew

According to pro growers, the best way to deal with powdery mildew is to prevent it in the first place. Here are some proven strategies:

1. Maintain Proper Humidity Levels

• Keeping humidity below 50% in indoor grow rooms.

• Using dehumidifiers or air conditioners in high-humidity environments.

2. Improve Air Circulation

• Using oscillating fans to keep air moving around plants.

• Pruning lower branches and excess foliage to increase airflow.

• Installing proper ventilation in grow tents or greenhouses.

3. Monitor Temperature

• Keeping grow room temperatures stable—ideally between 68°F and 77°F.

• Avoiding drastic day-to-night temperature swings.

4. Space Out Your Plants

• Avoiding overcrowding to reduce moisture buildup.

• Training plants using methods like low-stress training (LST) to allow for better airflow.

5. Keep Your Grow Area Clean

• Regularly cleaning grow tents, tools, and surfaces.

• Removing fallen leaves and plant debris promptly.

• Washing hands and change clothes if working with infected plants.

Can You Still Use Cannabis With Powdery Mildew?

It’s not considered safe to smoke cannabis flower that's affected by powdery mildew contamination. Even if you remove visible mildew, spores can linger in the buds.

Smoking or vaping mildew-affected weed can introduce harmful powdery mildew spores into your lungs, which may cause respiratory issues.

Stay Safe With High-Quality Weed

As a cannabis fan, staying safe while enjoying weed often means buying from the right source. Mold, mildew, and other big issues can wreak havoc on cannabis cultivation, and you want to have peace of mind that the weed you're smoking wasn't affected by these common problems.

This is just one of the many reasons to order third-party-tested, US-grown weed from Mood. All of our flower is cultivated by expert growers and tested for safety, purity, and consistency.

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