White spots on cannabis leaves are alarming because they can signify infection or disease that can lead the plant to even death. There are many reasons which can cause the white spots, including pests, fungal infection, or powdery mildew.

Battling White Spots on Cannabis Leaves

As you read through this article, you will receive experts’ advice regarding how to identify and treat the issue via the article. Don’t skip reading the article if you want to solve your white spots problem for good.

What Causes White Spots on Your Cannabis Leaves?

The white spots on cannabis leaves are caused by power mildew, thrips, and spider mites. In addition, the spots could even be some from fungus gnats that are fungal diseases that would harm the cannabis plant in the long run.

– Powdery Mildew

White powdery mildew is a surface-level fuzzy texture growth formed on the plants or leaves of plants, usually which are moist and decomposing or even living. The reason behind this Powdery Mildew, is a kind of fungus

It is a common fungal disease attributed to plenty of separate species of ascomycete fungi belonging to the order Erysiphales and is seen in a wide variety of plants, including cannabis plants and marijuana plants. The perpetrator fungus feeds off the leaves of the plants, and as a result, cannabis fan leaves and stems show white powdery spots. 

The spots get bigger and denser over time if the disease is not treated because nonproductive spores are structured, and gradually, the woolly white spots start to spread up throughout the green leaves.

The fungus affects lower leaves most, but the mildew infection can present on any part of your cannabis. However, the positive thing is powdery mildew is a disease that can be identified easily.

– Thrips

Pests, especially thrips, are very detrimental to cannabis health and can cause white spots on cannabis leaves. Thrips are tiny and thin insects with lopsided mouth parts belonging to the Thysanoptera order, and they are up to one mm long with decorated wings which make them look unique. 

There are around 6,000 species of thrips, but not all are harmful to plants. However, A good number of species act as vectors for almost 20 viruses that cause plant disease, as thrips live on plants and are reported to be digging and eating the leaves of the plants.

Reasons for White Spots on Cannabis Leaves

Thrips tend to sit on cannabis leaves all day and draw out the essence of the leaves, which causes silvery-white spots on them. These white worms, which look different based on the place and their age, fly only once a week as their wings are inconvenient for conventional flying.

For lifting themselves, these pests would set and throw to use an irregular circulation style with quick whirls near the wings.

– Spider Mites

Spider Mites are another bug, or pest, that brings white spots to the plants. White spots on your plant leaves indicate a daunting problem that the spider mites have attacked it. As the insects spread rapidly and can damage many crops in the twinkling of an eye, these insects must be treated quickly and sincerely.

Spider mites are very small insects that can be seen as red, black, yellow, and brown dots to human eyes. These insects belong to the Tetranychidae family and acari, or mites subclass. They are distributed among 1,200 species. 

You can spot them on the edge of branches or under the leaves, because spider mites live, guarding tiny, thin webs that look like silvery dots, and the mites also look like white dots on the plants. They feed off leaves cells by piercing them.

Whenever you are aware of their presence on your cannabis fan eaves, you should check the underside of the leaves and identify whether there are eggs or not. The existence of spider webs between fan leaves or flowers gives the sign that your plant is in danger.

– Fungus Gnats

Fungus gnats are also harmful pests to cannabis leaves. These small, dark flies look like gnats belonging to six families positioned in the Superfamily Sciaroidia. On the other hand, its larvae feed on plant roots, which hamper the cannabis’ ability to absorb water and other nutrients, damage roots, and hinder the plant’s growth. 

Especially when the cannabis is in its seedling or young condition, note that the damage can be dangerous. Fungus gnats live in the soil, not in the leaves or plants like most other bugs, and damage the roots of your plants. 


How To Stop White Spots on Cannabis Leaves?

You can stop the white spots by using Trifecta Crop Control Super Concentrate or TCCSC, spraying sodium bicarbonate, potassium bicarbonate solution, place another fungus which is the beauveria fungus. In addition, you can even place yellow sticky traps, and SM-90 oil, and lastly, applying neem oil can be a solution as well.

– Use Trifecta Crop Control Super Concentrate

Trifecta Crop Control Super Concentrate can is the best to use when to treat indoor white powdery mildew, just like the PM in flowering cannabis. 

You must apply this compact pesticide, fungicide, and miticide every three days to your infected plants. The measurement is two ounces per gallon till the disease is laid back. Once PM is under control, using one ounce per gallon each week is sufficient. Ensure your cannabis has access to fresh air.

Regarding powdery mildew treatment on cannabis that are placed outdoors, Trifecta Crop Control is a savior again, as it is as effective to treat outdoor powdery mildew as indoors. Make sure to apply two ounces of Trifecta Crop Control Super Concentrate every three days, just like for indoor PM problems, to take the disease under control. 

Solution for White Spots on Cannabis Leaves

When you are sure you are dealing with a white powdery mildew infection caused by the fungus, you have to take the situation seriously as it prevents the growth of your plant and causes it to wither and die gradually.

Once the condition improves, apply 1oz every seven days per gallon. However, weather and humidity are significant to get the best result of the treatment.

When the cannabis is flowering, you can treat PM up to 14 days before you reap the harvest with Trifecta Crop Control. The standard amount of applying Trifecta is two ounces per gallon every three days until you feel the condition of the fan leaves is improving.

On the other hand, when you identify Thrips that cause the white spots on your plants, you have to deal with the problem differently. Applying Trifecta Crop Control works great in this case, also. Apply two ounces of Trifecta Crop Control Super Concentrate per gallon and use it.

However, treating the problem with only Crop Control is not easy. You have to spray fine mist atomizers with a deluge sprayer. But ensure to spread it to their thorax area to make them suffocate as their breathing organs lie there.

– Use Sodium Bicarbonate

After the infestation is healed, sterilization of the room is a must to destroy if any mold spores are still alive, which can cause trouble in the future. For sterilization, you can use Sodium bicarbonate and water solution. This is because baking soda or sodium bicarbonate is a handy solution to the white powdery mildew issue of cannabis leaves.

Place the mixture of one teaspoon of baking soda in one quart of water in a spray bottle container and spray the infected plants. It holds a high pH, which powdery mildew cannot tolerate. Use an Ozone generator and ensure a good ventilation system before using the room again. 

– Prune the Leaves

If you find the disease after it gets intense, you must prune off all infested fan leaves and stems and destroy them by burning them or putting them in the trash can. Moreover, you must stop giving compost to your infected cannabis because, in such cases, any fungus would spread on any other crops.

Predators bugs, including ladybugs, six-spotted thrips, bogeyed bugs, etc., can be collected from nurseries and are very good at destroying mites. However, if any leaf or the whole plant is infected severely, it should be removed and destroyed.

– Spray Potassium Bicarbonate

Potassium bicarbonate works fine in PM disease as well, you must be spraying them on as you have mixed it, it works best if you place it in a spray bottle. 

It provides a quick and effective solution as a contact fungicide by killing powdery mildew spores. This is another way to get rid of the white tiny circles that are on the leaves and are basically contaminating them.

– Place Beauveria Fungus

Beauveria, a useful fungus, can be used alongside Crop Control which has been proven beneficiary in destroying thrips and even Fungus Gnats. Using both crop control and the fungus in the rotation will give the best result.

– Place Sticky Traps

Another way to kill thrips is using blue sticky traps in the infected leaves as they are allured to vibrant colors. Besides, predatory bugs such as green lacewings, specific species mites, minute pirate bugs, etc., can be used to kill thrips. 

However, when there are not many thrips, you can solve the problem by cutting the infected area. You can prune the plant above the roots avoiding cutting terminals to fight the thrips.

When it comes to gnats however, you can use yellow sticky traps as the yellow color is very attractive to gnats. The bug will die after getting trapped in it.

– Spread Neem Oil

When spider mites attack your plants, essential oils are good options, as the neem oil knock down the bugs’ central nervous system and kill them. 

Interestingly, spider mites are astute and can web like a canopy to survive the spray. You must remove the webs before spraying the plants to receive the best outcome. Diatomaceous earth is also helpful in slowing down the infection. Use the powder on the leaves, and the mites will die.

A Complete Guide to Identification and Remedy

– Use SM-90 Oil

Using SM-90 oil is a great option as a natural remedy for gnat larvae, as it does not pose a risk to root health. Besides, Neem Oil can be used against fungus gnats larvae.

You can use food-grade Diatomaceous Earth to kill these bugs, as the rock powder pierces the gnats’ exoskeleton and dehydrates them till their death. Essentria IC3 Insecticide and taking away the insects’ habitats are great ways to destroy fungus gnats.


Now you know how to recognize the specific cause behind the white spots of your cannabis fan leaves and how to treat them.

Let’s make a quick summary to look at the reasons and solutions for the last time.

  • Different factors, including pests and fungi, can cause white spots on cannabis leaves.
  • White spots caused by the fungus are known as white powdery mildew, these are primarily the main factor.
  • You can get rid of them by placing sticky traps, or you can even spray them way with neem oil.
  • Trifecta Crop Control, baking soda, predatory bugs, colorful traps, etc., can be used to solve the problem, and their uses are different based on various causes.

So, follow our experts’ advice, and enjoy cannabis cultivation being free from the white spots problem for a lifetime.

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