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White Powdery Mildew on Cannabis Plants

Powdery mildew on cannabis leaf

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White powdery mildew on cannabis is one of the most problematic of all cannabis pests and diseases. Powdery mildew can be tricky to treat and extremely harmful to harvests.

How to identify white powdery mildew on cannabis plant

Although WPM is a frequent yet significant hazard to cannabis plants, it’s not always easy to identify and treat. WPM shows as white spots on cannabis leaves or gray powdery-fuzzy residue on immature leaves of a cannabis plant. Though powdery mildew normally starts on leaves, it soon spreads to the buds, rendering them useless essentially. It is important to treat white powdery mildew as soon as it appears.

White spots on fan leaves is likely White Powdery Mildew on cannabis
White spots on fan leaves are likely White Powdery Mildew.

White spots on fan leaves may be an indicator of powdery mildew cannabis. If the infection is severe, you can smell decaying foliage. If you see it early, you can eliminate it from plants with the correct treatment, but you should throw away any buds with WPM  since they are likely to contain more spores than your eyes can see.

What causes white powdery mildew on cannabis?

  • High Humidity

Even while powdery mildew cannabis thrives in damp environments, it doesn’t imply it needs water. It’s important to maintain good humidity for growing cannabis regardless. WPM needs a high-humidity growing environment to get going. It seems to be a concern since immature cannabis plants thrive in both warm and humid (40 percent -60 percent RH). Fortunately, the combination of high humidity and low/no airflow is generally enough to produce a problem.

A dehumidifier is a good option for those in areas with high relative humidity, such as the southern United States or the United Kingdom. Try a a lower relative humidity (around 45%) to help avoid white powdery mildew and mold during the flowering stage.

  • Low or No Airflow

When the air in a grow room is constantly changing, it’s difficult for White Powdery Mildew to establish itself. While high humidity is essential for WPM’s survival, insufficient ventilation initially allows it to settle in. You can avoid a great majority of powdery mildew nug difficulties using a simple oscillating fan.

  • Poor Airflow

A lack of fresh air or air circulation allows WPM spores to spread much easier around the grow space. Confined and unventilated grow spaces allow powdery mildew to grow much easier, therefore it is important to maintain proper ventilation.

  • Leaf-to-Leaf Interaction

Leaves that come into contact with one other are more likely to develop WPM because of the moisture between them. Untrained bushy/leafy plants with much new vegetative growth are particularly vulnerable since their leaves are often smashed together as they attempt to reach for the sun.

Advanced growers may reduce the number of potential landing sites for White Powdery Mildew by defoliating part of the fan leaves entirely shaded from the grow light. Defoliation also enhances yields by freeing up energy for the plant to use.

How to get rid of white powdery mildew on cannabis?

Clean the white powdery mildew from the leaves

Get some water and paper towels (tap water is OK). Paper towels should be soaked in water and gently remove cannabis leaf mold from the afflicted leaves while being cautious not to jiggle any leaves with spores on them. More spores will attach to the cloth if you use a damp one instead of letting them go into the air. If you don’t have disposable paper towels on hand, you may still use them to prevent spores from spreading from one leaf to the next.

Ensure that plants are adequately ventilated and have enough air movement

Even if your grow area is entirely devoid of any airflow or ventilation, installing only two fans can significantly lower your risk of coming into contact with WPM while also improving the health of your plants. As a rule of thumb, one fan should rotate and blow air softly over your plants. Powdery mildew on cannabis will have a hard time settling down if there isn’t enough breeze to flutter the leaves of the plants softly. Place a second fan in your grow room with its blades directed outward to replace stale air with fresh air. When you have a fan pointed out of your grow room, you’ll be able to remove old air from the area and bring in fresh air. New air will be brought in, utilized, circulated, and finally expelled. Two fans are the minimum need.

As a Weapon, Use the pH of the Leaf Surface

Even though powdery mildew cannasbis spores may be hard to eradicate from the environment, producers may at least make it more difficult for diseases to spread. If you want to inhibit powdery mildew’s capacity to establish itself in a crop, it is necessary to alter the pH of the leaf surface.

Sulfur-containing treatments will lower the pH of the leaf surface, whereas potassium bicarbonate-based compounds would boost it. It’s best to avoid using these treatments on fully bloomed plants, even when they’re organically approved.

Dealing with white powdery mildew outdoors 

You can interrupt the spread of white powdery mildew on cannabis by physically removing any damaged leaves if found early enough. Start by looking for white spots on cannabis leaves. To prevent the transmission of germs, this should be done using sterile shears that have been cleaned thereafter. Most powdery mildew is not discovered until it has progressed beyond a few leaves. At this time, the producer must select whether to employ chemical or organic fungicides.

Chemical fungicides sold over the counter abound on the market. Chlorothalonil is a reliable remedy for this problem. Use this active ingredient to identify insecticides. Thiophanate-methyl, myclobutanil, propiconazole, and tebuconazole are other active chemicals that you can use in this medication. To avoid the illness developing a resistance to a single therapy, use at least two distinct formulations. It is valid for both conventional and organic solutions.

Natural and organic approaches are available to producers interested in tackling this issue. Use organic and natural nutrients primarily, as they are most effective, however, stressed or overheated plants may suffer with added nutrients.

Stop white powdery mildew before it becomes a problem

The most excellent method to avoid a disease is to avoid getting it in the first place, just like everything else. However, if you can prevent powdery mildew from forming in your producing regions by using pesticides and other measures, you will reap both physical and metaphorical rewards.

Heat, gloom, and wetness are all favorites of fungi. Take steps to prevent the occurrence of all three of these environmental elements coming together for an extended period. Proper lighting, ventilation, and spacing of your cannabis plants are essential for a healthy crop.

Avoid overwatering plants, and focus on watering correctly to help prevent WPM. Powdery mildew is less prone to grow on dry leaves.

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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. While Ed has a particular penchant for the SCROG, Schwazzing and Mainlining techniques in his own garden, he has basically mastered every growing technique which has allowed him to choose the ones he personally favors. When it comes to pests and diseases, Ed draws on his own experiences as a novice grower way back in the day and builds upon his own learning curves to provide comprehensive guidance on dealing with plant problems in a pinch.
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. While Ed has a particular penchant for the SCROG, Schwazzing and Mainlining techniques in his own garden, he has basically mastered every growing technique which has allowed him to choose the ones he personally favors. When it comes to pests and diseases, Ed draws on his own experiences as a novice grower way back in the day and builds upon his own learning curves to provide comprehensive guidance on dealing with plant problems in a pinch.

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