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How To Deal With White Spots on Fan Leaves

December 13, 2022

The appearance of white spots on fan leaves is generally a sure sign that something is wrong with your cannabis crops. The earlier you treat your infected marijuana plants, the better your chances of saving your grow.

Do you want to keep your cultivation area free of pests and pathogens? Keep reading to discover more about identifying, treating, and preventing white spots. We also delve into what they mean for your cannabis plants.

Let's get into it!

Causes of white spots on fan leaves

White spots on marijuana leaves indicate that your plants aren’t happy. To get your babies back on track, you need to identify the reason for the blemishes and treat them accordingly.

Thrips, spider mites, and powdery mildew are the primary causes of white spots on weed. Knowing how and why these cannabis pests and pathogens invade plants is vital for every grower.

Let’s explore them below.

Fungal diseases 

Cannabis plants are susceptible to fungal diseases. These pathogens are highly detrimental to your crops and can spread quickly.

Powdery mildew on cannabis is the primary fungal disease that presents as white spots. It inhibits the plant’s ability to photosynthesize by attacking its foliage.

In the early stages of infection, it presents as small white spots on fan leaves. As it spreads, which it does at a rapid pace, the small dots turn into a white fuzz covering the entire leaf surface.

Your climate is the main factor in the occurrence of powdery mildew. The spores multiply in cool, humid conditions. Climate control is vital in combating and preventing this fungus from infecting your grow. 

Excess cannabis fertilizer speeds up growth, making plants more susceptible to fungal disease as powdery mildew tends to attack new foliage.


Spider mites and thrips are common cannabis pests that cause white spots on weed plants.

spider mites on cannabis

Spider mites are tiny yet can cause significant damage. They’re translucent and come in shades of red, brown, green, black, and orange. Early detection is vital, as these pests get to work quickly. 

The mites feed on the foliage and present as white spots on the fan leaves of your plants. They drain crops of their nutrients and leave small yellow markings in their wake. They reproduce rapidly and thrive in hot, dry conditions.

Thrips are tiny, yellowish-white pests with elongated bodies and wings that help them fly from plant to plant. They leave a silvery, sheen stain on the leaves of cannabis crops. This mark results from the pests sapping the leaf of its nutrients and female thrips laying their eggs. 

They tend to be most common in indoor marijuana grows and reproduce fast.

Prevention is key when it comes to white dots on cannabis leaves. Taking the time to check your plants regularly is of great importance for a healthy harvest.

If these nasty critters take up residence in your grow room, equip yourself with knowledge about weed leaf problems and hand them their eviction notice.

How to get rid of white spots on weed leaves

The first step in ridding your plants of white spots on cannabis leaves is identifying what they are. From the above information, you should be able to determine whether they’re spider mites, thrips, or powdery mildew.

Let’s take a look at your treatment options:

  • Thrips: Place yellow sticky traps around your grow area to catch these small insects. Use potassium soap or neem oil every two to three days. Be sure not to use neem oil during flowering, as it can negatively affect the taste of your weed.
  • Spider mites: Lower your temperature, increase humidity, and improve airflow in your grow room to slow reproduction. Prune and dispose of all infected leaves far away from your growing environment. Gently wash down the remaining plants to eliminate any remaining spider mites. Spray safe, organic insecticides on your leaves but avoid the buds at all costs.
  • Powdery mildew: Attack this problem head-on with organic treatment methods such as potassium bicarbonate or baking soda. Use them up until two weeks before harvesting. Increase the airflow through your grow area and give your plants plenty of space to spread out.
Spray safe, organic insecticides on your leaves

Can I prevent the appearance of white spots on cannabis leaves?

We can’t stress this enough: prevention is key. Here are some tips to help you avoid white spots on your weed leaves:

  • Keep the temperature and humidity levels stable and in the recommended range of the particular marijuana strain.
  • Don't leave decaying or old plant matter lying around your plants. They’re breeding grounds for pests and fungi.
  • Follow a strict IPM (Integrated Pest Management) regime to prevent unwanted critters and diseases in your grow area.

Where to from here?

Finding white spots on cannabis leaves can be scary, but theres no reason to panic.

Control pests like thrips and mites by thoroughly checking your plants to ensure they aren't carrying unwanted visitors. Prevent powdery mildew by keeping a controlled climate and ensuring unrestricted airflow.

Find an unrivaled selection of cannabis strains with impeccable quality at our online seed bank. We stock cultivars with premium genetics to give you an enjoyable, hassle-free cultivation experience.

About the Author: Kyle Kushman

Kyle Kushman is a legend in the cannabis community. He is the modern-day polymath of pot: cultivator, breeder, activist, writer, and educator. After winning no less than 13 Cannabis Cups, there’s nothing this guy doesn’t know about indoor growing - he’s been there, done it, and is still doing it to this day!

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