Powdery Mildew - Definitive Guide To Prevention And Treatment

One morning you step into your grow room to check your plants, and you notice something alarming.

Seemingly overnight, little white splotches have appeared on the leaves of one of your plants. You have found a case of powdery mildew, which is one of the most common fungal infections growers will experience.

If you are combating powdery mildew currently, don’t worry. We will explain how to eradicate it easily. But first, let’s discuss it in more detail, and explain how you can take steps to prevent it from infecting your plants in the first place.

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Powdery Mildew - Definitive Guide To Prevention And Treatment


One morning you step into your grow room to check your plants, and you notice something alarming.

Seemingly overnight, little white splotches have appeared on the leaves of one of your plants. You have found a case of powdery mildew, which is one of the most common fungal infections growers will experience.

If you are combating powdery mildew currently, don’t worry. We will explain how to eradicate it easily. But first, let’s discuss it in more detail, and explain how you can take steps to prevent it from infecting your plants in the first place.

What is powdery mildew?

Powdery mildew, referred to as PM for short, is a fast acting, harmful fungus. It is airborne, and can overtake an indoor garden incredibly quickly.

PM is a common intruder in the grow room. It can be easy to eradicate if caught early, but spreads so rapidly that it needs to be addressed immediately. This is why it is important to check the foliage of your plants on a daily basis.

If left untreated, PM will overtake your entire garden. This can lead to a halt in growth, bud rotting, and eventually, the death of plants.

What does powdery mildew look like?

Powdery mildew is pretty easy to differentiate from other fungi and plant diseases. Some symptoms of powdery mildew include:

  • White patches of powder on leaves
  • Mottling or a mosaic pattern on leaves
  • Pale colored leaves
  • Older, lower growth is affected first, and then upper, newer growth
  • Wilting and drooping plants

How do you prevent powdery mildew?

spray for powdery mildew Spray with a fungicide to combat PM

An ounce of prevention is worth a pound of cure, and preventing PM in your indoor garden is as simple as removing moisture, circulating air, and setting up a proper ventilation system.

Humidity

Excess humidity creates a breeding ground for powdery mildew, along with many other fungi. While plants are vegging, you should keep humidity between 40-60% to encourage fast, healthy growth.

While this is essential to cultivating strong plants, you need to be careful about excess moisture leading to PM. If you are having trouble controlling your humidity, you may consider a dehumidifier.

Ideal-Air Dehumidifier

Ideal-Air Dehumidifier

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Quest CDG Dehumidifier

Quest CDG Dehumidifier

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Lack of airflow

Another common culprit of powdery mildew is a lack of airflow. Make sure you are circulating air effectively in your grow room or grow tent. Using oscillating fans and clip on fans will keep air moving, which not only strengthens stems, but also aids in pest and disease control. Stagnant air creates an environment conducive to bug and fungus problems.

To learn more about fans and blowers, check out our full guide to using inline fans and blowers for grow room ventilation!

Note - if you do have a powdery mildew outbreak, it may be best to turn your fans off until it is under control. Your fans will circulate the spores around the room, spreading the disease quicker!

Grow room ventilation

Poor ventilation will keep fresh air from entering your grow room, and increase the likelihood of powdery mildew infecting your garden. If you are already battling PM, poor ventilation will allow it to spread much quicker than normal.

You need to be exchanging the air in your grow room or grow tent at least every 3-5 minutes. A ventilation system consists of an intake fan and filter to bring in fresh air, and an exhaust fan and filter to remove hot, smelly air.

A HEPA intake filter will greatly reduce the chances of contaminants entering your system, and a carbon exhaust filter will help remove odors from the grow room. Both are essential components of a ventilation system.

If you want to learn more about setting up a proper ventilation system, check out our full guide on grow room atmosphere and ventilation.

Leaf to leaf contact

Leaf to leaf contact can also contribute to powdery mildew. A very dense canopy will create a micro-climate with higher humidity levels than ideal. This can be mitigated by housing fewer plants in the growing area, and attention to detail while pruning.

Defoliation is a great way to increase airflow within your plants, and can actually increase growth. By pruning large fan leaves, other areas of your plant can receive light.

Be careful not to remove too many fan leaves, as this can shock the plant and stunt growth.

For more information on controlling your environment, click here.

How to treat and eliminate powdery mildew

inspect weed Inspect plant foliage daily for PM

If you have taken all the steps to prevent PM and still find yourself dealing with it, don’t worry! If you catch it early, eradication can be pretty simple. Before you go crazy with the fungicides, assess how serious the outbreak is.

If there are just a few affected leaves, try removing them and surrounding leaves. Watch the plant(s) closely, and at the first sign of continued infection, apply a fungicide.

PM will never go away on its own, so if you do not take steps to treat it, it will only worsen.

Fungicides for powdery mildew

At Hydrobuilder, we carry a number of products you can use to fight powdery mildew, such as:

View our full fungicide category here

Home remedies for powdery mildew

These products are all safe for you and your plants, and will generally require the use of a garden sprayer or fogger. There are also a few home remedies you can try, such as:

  • Milk Spray ( 10-12oz per gallon of water, 1:9 Ratio)
  • Hydrogen Peroxide 35% (1 tsp per gallon of water)
  • Baking Soda (“Sodium Bicarbonate” 2 Tablespoons per gallon)
  • Apple Cider Vinegar (2-3 Tablespoons per gallon of water)

There have been stories of success with these treatments, but we recommend going with something proven to work. With how quickly PM can overtake and indoor garden, you don’t want to waste time testing things.

As mentioned earlier, the best way to fight powdery mildew is preventing it from infecting your plants in the first place. Put an emphasis on controlling your environment, and you will be far less likely to deal with any pests and diseases.

To learn more about common indoor gardening pests, check out this article!