What Causes Powdery Mildew on Cannabis?

Find out what causes powdery mildew on cannabis and how to prevent it from happening to your plants.

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Powdery mildew is a type of fungus that can affect a variety of plants, including cannabis. This disease is characterized by white or grayish powdery spots on the leaves and stems of the plant. Powdery mildew can occur indoors or outdoors, and it can spread quickly if not treated properly. If left unchecked, powdery mildew can cause your cannabis plants to yield fewer buds or even die.

There are a few different things that can cause powdery mildew to form on cannabis plants. One of the most common causes is high humidity levels. This is why powdery mildew is more common in humid climates or during the summer months. Another cause of powdery mildew is bad air circulation. This can happen if your grow room has poor ventilation or if there are too many plants crammed into a small space.

If you suspect that your cannabis plants have powdery mildew, it’s important to act quickly. There are a few different ways to treat powdery mildew, but the most effective method is to use a fungicide specially formulated for this purpose. You can also try using a homemade solution made with baking soda and water. Whichever method you choose, be sure to follow the instructions carefully and apply the treatment at the first sign of powdery mildew.

The Biology of Powdery Mildew

Powdery mildew is a type of fungal disease that affects a wide range of plants, including cannabis. The powdery mildew fungus uses small, thread-like structures called hyphae to infect plant tissues and produce spores. These spores are spread by wind and water to other plants, where they germinate and produce new infections.

The Fungus

Powdery mildew is caused by a fungus called Erysiphe cichoracearum. This fungus is able to infect many different types of plants, including cannabis. The fungus spreads through the air, and can be transported on clothing, hair, or any other type of material that comes into contact with infected plants. Once the fungus is established on a plant, it will begin to produce spores. These spores are what allow the fungus to spread to other plants.

Powdery mildew tends to prefer warm, humid conditions. It can also survive in cooler temperatures, as long as there is enough moisture in the air. The fungus will usually only infect leaves that are already damaged or stressed in some way. This could be from too much or too little water, nutrient deficiencies, or even just from being brushed up against something. Once the fungus has infected a leaf, it will begin to spread throughout the plant. It can eventually kill the plant if left unchecked.

The Spores

Powdery mildew spores are ubiquitous in the air and can be transported long distances by the wind. The spores do not require water to germinate and can infect a wide range of hosts, including most cultivated plants and many weeds. The disease is often first noticed as small, circular, powdery white lesions on the upper surface of leaves. These lesions eventually expand and coalesce, leading to extensive white powdery growth on the leaves, stems, flowers, and fruit of susceptible plants.

The Conditions Powdery Mildew Needs to Thrive

Powdery mildew is a type of fungi that affects many different types of plants, including cannabis. This disease is caused by a variety of conditions, including high humidity, poor air circulation, and high temperatures. Let’s take a closer look at each of these conditions and how they contribute to powdery mildew.


Warmth is one of the three primary environmental conditions that powdery mildew needs in order to thrive. The ideal temperature range for powdery mildew to grow and reproduce is 59-77°F (15-25°C). However, powdery mildew can still grow at temperatures as low as 41°F (5°C), though its growth will be greatly slowed. Likewise, powdery mildew can still reproduce at temperatures as high as 95°F (35°C), though again its growth will be slowed. The bottom line is that powdery mildew can survive and reproduce in a relatively wide temperature range, making it difficult to prevent simply by controlling the temperature.


Powdery mildew needs two things to survive and reproduce: a living plant and moisture. Once it’s settled on a cannabis leaf, it’ll happily feast on the water inside the leaf cells, spreading its hyphae throughout the plant in search of more water and food.

Powdery mildew is most commonly seen in humid environments, or when there’s too much space between plants (or leaves) and not enough airflow. The lack of airflow prevents moisture from evaporating quickly, which creates an environment where powdery mildew can thrive.

Poor Air Circulation

Powdery mildew spores love still air. If your grow room has poor air circulation, the powdery mildew spores will be able to float around and land on your cannabis leaves unhindered. The key to preventing powdery mildew is to keep the air in your grow room moving. Use a fan to circulate the air and prevent the formation of stagnant pockets of air where powdery mildew can take hold.

How Powdery Mildew Affects Cannabis Plants

Powdery mildew is a type of fungi that affects cannabis plants. This disease is caused by a lack of ventilation and poor air circulation. The spores of the fungi can spread quickly and infect other plants. Powdery mildew can cause the leaves of the plant to turn yellow and the buds to become stunted.

Direct Effects

Powdery mildew is a fungal problem that can affect any type of plant, but it is especially common in cannabis. The fungus grows on the surface of the plant and produces a white or gray powdery substance. Powdery mildew does not usually kill the plant, but it can severely reduce the yield. In severe cases, the entire plant may be covered in mold and might need to be destroyed.

Powdery mildew thrives in warm, humid environments. It is often found in greenhouses or indoor grow operations. The fungus can spread quickly and is difficult to control once it gets started. Prevention is the best approach to dealing with powdery mildew.

Sanitation is important for preventing powdery mildew. The fungus can spores can survive on dead leaves or other plant material. Any infected material should be removed from the grow area and destroyed. The grow area should be kept clean and free of debris.

It is also important to keep the plants themselves clean. Powdery mildew can spread from one plant to another, so infected plants should be isolated from healthy plants. Infected leaves should be removed and destroyed. Plants should be routinely inspected for signs of powdery mildew and treated immediately if any are found.

There are a number of chemical treatments that can be used to control powdery mildew. These include fungicides, such as sulfur, copper, or mancozeb. These products must be applied regularly and as soon as any signs of powdery mildew are noticed. Plant oils, such as neem oil or jojoba oil, can also be effective at controlling powdery mildew when used as a preventative measure or at the first sign of an infection

Indirect Effects

Powdery mildew can cause indirect effects on your cannabis plants even if the mold isn’t physically touching them. For example, if your plants are surrounded by powdery mildew-infected leaves, the mold can spread to your plants through the air. Although powdery mildew doesn’t usually kill cannabis plants outright, it can severely stunt their growth. In fact, powdery mildew is often responsible for preventing Cannabis plants from reaching their full potential size.

Prevention and Treatment

Powdery mildew is a type of fungal disease that can affect cannabis plants. The fungus affects the leaves and buds of the plant, causing them to turn yellow or brown. The fungus can also cause the leaves to curl up and fall off. In extreme cases, the plant may die.


Powdery mildew can be prevented with a few simple measures. Firstly, ensure that your plants have plenty of air circulation. Good air circulation will help to keep the leaves dry, which will make it more difficult for powdery mildew to take hold. Secondly, water your plants in the morning so that the leaves have plenty of time to dry off before nightfall. Nighttime is when powdery mildew thrives, so keeping the leaves dry is crucial. Finally, try to avoid mechanically damaged leaves, as these are more susceptible to powdery mildew infections.


Powdery mildew can be controlled in several ways. You can remove the infected leaves, avoid overhead watering, improve ventilation, and increase air circulation around your plants. You can also use fungicides, but make sure to read the labels carefully and follow the directions. Some fungicides are not safe to use on edible plants.


Powdery mildew is a type of fungal infection that can affect cannabis plants. The most common symptom is the appearance of white, powdery spots on the leaves, although other parts of the plant may also be affected. Powdery mildew is caused by a variety of fungi, including Oidium cannabis and Erysiphe cichoracearum. These fungi thrive in warm, humid conditions and can spread quickly from one plant to another.

Prevention is the best defense against powdery mildew, as current treatments are not very effective. To prevent the spread of powdery mildew, it is important to avoid overhead watering, water only at the base of the plant, and prune infected leaves. If you do find powdery mildew on your plants, you can try removing infected leaves or spraying them with a fungicide. However, these measures are not always effective and may not prevent the fungus from spreading.

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