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White Spots on Fan Leaves

white spots on fan leaves

White spots on fan leaves are a sure sign of a disease or pest – it could even be a form of bugs on your cannabis plants.

Cannabis farmers often encounter the problem of white spots on fan leaves. In the majority of cases, it is because of the following:

  • White powdery fungal infection. (The most prevalent kind is powdery mildew on cannabis)
  • A spider mite infestation is the primary cause of pest problems.

Mold spores move from plant to plant, causing white powdery mildew. There are a variety of factors that might have an impact on your plants, including:

  • Wind
  • Air Ventilation
  • Pets

How can you recognize a white spots infection on leaves?

Spider mite white spots on fan leaves infestation, and a WPM infestation may seem similar at first glance. Consequently, pinpointing the source of your issue might be a challenge. It should go without saying that the first step in resolving a problem is identifying what the problem is.

In its early stages, the white spots on fan leaves during flowering are caused by a fungus known as white powdery mildew (“WPM”). First, you will damage the lowest leaves of the plant the most. Scattered patches will become more prominent and eventually encircle the plants as the mold spreads to other locations. The following are the most important indicators to watch out for when diagnosing if you have a mite or WPM issue.

No bugs around

If your plants are covered with white spots, and you can’t find any bugs, other than fungus gnats, you probably have white spots on cannabis leaves issue.

Spot appearances

Dots in the WPM range seem more like splotches or fuzzy round patches on the leaves of plants. Spotty and occasionally withered patterns are common. Please keep in mind that you’re searching for white dots. So, if you see yellow or brown blotches on the leaves, you may have more than mildew on your hands. Leaf septoria, the medical term for yellow-spotted leaves, is another name for this condition.

The appearance of the leaf

There are white specks on the green cannabis plant leaves, making them easier to see.

How to prevent WPM and what leads to it

A lack of adequate indoor growth conditions is most likely to blame for the white spots on cannabis leaves (which do not originate from spider mites). The following are some of the most typical causes of the white spots on fan leaves – mildew:


For seedlings, a humidity level of 70 percent or more is ideal. However, WPM thrives at roughly 70% humidity for plants and flowers. Keeping humidity levels below 40 percent is essential for blooming; thus, you should avoid growing seedlings with your cannabis plants. As a result, using your hygrometer, be sure to check the humidity level in your grow room frequently.


Check out our other article to find the best humidity for growing cannabis!


Mold-proof strains

When shopping for cannabis, look for mold-resistant varieties.

Air circulation

WPM dots are more likely to appear when your plants are overcrowded. Because of this, you must ensure that you uniformly space your cannabis plants and that you get the suitable grow tent size for the number of plants you want to produce.

Spaced out cannabis plants
Well-spaced out cannabis plants. They can be grown closer to each other, but space them out according to the space that you have

Buy an excellent circulating fan for your growing area and know how to utilize it.

Lack of Light

When plants aren’t getting enough light, they’re more vulnerable to WPM. If you don’t already have a decent timer, purchase one now. When cultivating a particular strain, you’ll need to make sure your timers function and that you schedule them accordingly.


Over-fertilizing encourages plants to develop too rapidly, which is not suitable for WPM’s taste in plants. When your cannabis plants grow excessively quickly, they are more vulnerable to WPM. Remember that too much fertilizer might be detrimental to the health of your lawn. Be careful to use the proper fertilizer rate based on the total number of plants in your yard.

Poor air quality

If the air quality in your growing location is poor, white spots on pot leaves might spread more rapidly. As a result, investing in an air filtration system for your growing space is a smart move.


You can create conditions favorable to mildew growth when a growing region is both dry and humid at the same time. Make sure your plants get enough water, and you’ll be OK.

How concerned should you be about white-spotted leaves on fans?

The white specks on the top of your cannabis plants are where WPM begins. If you don’t treat it, your plants will develop a mold or fungus-like material. White spots on leaves cannabis will eventually cover an extensive section if left uncontrolled. Because it slows photosynthesis, the mildewy layer makes it difficult for your plants to obtain the light they need to thrive. Once your plants start turning yellow, they’ll soon perish unless you do anything about the condition.

How do you fix WPM?

You can fix white spots on my cannabis leaves in various ways, including organic, do-it-yourself, and commercial. Finally, don’t put it off to minimize the harm. To reduce the damage, you must address the issue as soon as possible to prevent the WPM from spreading further throughout your plants. In addition to avoiding cannabis white spots on leaves, you can apply several of the following remedies

Fixing WPM using homemade techniques

Baking soda

You may avoid and perhaps treat a WPM issue by combining baking soda and liquid soap. To make this dishwashing detergent, you need to add 1 Tblsp to 1/2 tsp of liquid soap (non-detergent dish soap) to 1 gallon of water.


Using mouthwash may help prevent cavities by killing the bacteria that cause them. You can eradicate WPM with the aid of the germ-killing qualities of mouthwash. Three parts water to 1 part mouthwash is all you need for this recipe. (Warning: this is quite strong; use caution when applying to young plants.)


You can fix white spots on leaf cannabis with milk. For the most part, it’s reserved for cukes and squash. On the other hand, you could wish to try this on cannabis. The recipes call for a simple 3:1 milk-to-water ratio.


You can treat white dots on cannabis and prevent them using a variety of fungicides. Amazon’s top-selling fungicide for WPM is Trifecta’s fungicide, specifically designed to help prevent and treat WPM.

Preventing white spots on your plants is the best way to avoid them in the first place. As a result, you must adhere to the industry’s accepted standards for indoor gardening. First and foremost, if you are a novice grower, I recommend using strains that are resistant to mold. After that, ensure you’re following the ideal methods for producing cannabis. Example: Don’t over-fertilize; keep humidity at the right amount. You will also have less of a problem if you follow the recommended procedures for cannabis production in the event of a WPM.

Picture of Ed Rushford

Ed Rushford

Ed Rushford’s impact on cannabis growing is undeniable. Though he tends to focus primarily on 2 areas, plant training techniques and dealing with disease, pests, and other problems, he has offered many insights into how cannabis plants live and grow. That’s not to say that Ed is unfamiliar with the complete life cycle of cannabis, from seed to harvest, but he uses his widespread knowledge to hone in on the minutia and niche areas of growing cannabis. Ed’s goal is to spread knowledge and allow for everyone to become better growers. About this Author

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