Keep Bud Rot and Mildew From Claiming Your Harvest
Identify bud rot, powdery mildew, and sooty mold before they spread.
According to The Hill, did you know that almost half of US adults said in a poll that they’ve tried medical marijuana? This percentage was 49% out of all the adults polled, which is much higher than it has been in the past, at 40% four years before 2021.
If you’re one of the many Americans who has tried medical marijuana, and you grow your cannabis, then you don’t even have to go out to buy medical marijuana products.
However, if you’ve noticed something gray on your plants, you might be worried. What is it? Chances are, it’s cannabis mold. Does this make you feel even more worried? Fortunately, there’s no need to.
Here’s everything you need to know about mold in cannabis, including what signs to look out for, as well as how to prevent and treat this mold. Along the way, you’ll see where Tri-Oxy ozone water treatment systems fit into a clean, healthy grow.
Finally, your cannabis plants can be healthy. Read on to learn more.
Before we go into cannabis mold prevention and how to get rid of mold on cannabis plants, we’ll review the signs of different types of cannabis mold. This way, you can identify whether mold is the issue—and, if it is, know what type is negatively impacting your plant’s health.
Additionally, there’s the added benefit that if you identify the mold early on, you’ll avoid having it cause too much damage over time to your plant.
Botrytis is known colloquially as bud rot or gray mold. This mold can occur both in dried buds and growing plants, but it’s most common in outdoor plots after a lot of humidity or heavy rainfall. Often, this fungus originates inside moist, dense buds. Only after that does it usually become visible outside of the buds.
Botrytis can enter the plant’s tissue, remaining dormant until the plant’s environment is conducive to the spread of the mold. Then, when this happens, it will rapidly rot the cannabis tissue.
How does it do this? This type of mold produces toxins and enzymes that destroy the cannabis plants’ cell walls. According to research, this might cause the plant host to begin cellular death. However, it can be challenging to spot because bud rot is so insidious.
However, some signs include yellowing or dying leaves near the cola, gray or brown patches that look like lifeless, discolored- or limp-looking colas, and plant tissue that feels dry or crumbles when you touch it.
If you notice any of these signs, you can break apart buds that are suspicious-looking. If the dark mold is hidden inside, you know your cannabis has bud rot.
Powdery mildew is a type of mold that appears on the flowers and leaves of the cannabis plant. It often appears when cannabis is growing in an environment that has a lack of airflow and moisture. If it appears on the flowers, it could become a systemic problem quickly.
Signs of powdery mildew include white, circular spots that look like a light flour dusting, white spots that appear on the leaves’ upper sides (instead of the underside ones), and the drying out and yellowing of leaves.
Another sign of powdery mildew is the more mature plants becoming disfigured, especially as the powdery mildew’s spread progresses.
Another type of cannabis mold is sooty mold. This mold resembles soot. Sooty mold doesn’t directly attack the cannabis; it grows in common garden pests’ secretions. So if your cannabis has been infested with whiteflies or aphids, you might notice sooty mold.
Sooty mold grows more often in plants that are grown indoors.
Signs of sooty mold include dark black, small patches on the cannabis fan leaves, plant growth hindered by impeded photosynthesis, and the affected areas having a grimy appearance.
Additional signs include the affected areas being sickly and the foliage yellowing as the mold obstructs the light coming from the sun.
Because humidity and warmth are necessary for growing medical marijuana, mold growth can be likely. Mold often requires humid and warm conditions for its growth. As a result, when you’re growing cannabis, you’re often doing a balancing act when trying to avoid mold growth.
In addition to the cannabis growing environment being a reason why mold might grow, other factors that might contribute to the growth of mold include poor plant health, overwatering, and humidity.
Considering how easy it can be for mold to grow on your cannabis plants, you must take whatever preventative measures you can to avoid mold growth. These include the promotion of air circulation, using organic fungicides, and more.
One of the most effective ways you can prevent mold growth is by promoting air circulation. To do this properly, make sure that the air that circulates moves to rustle the cannabis leaves gently. By ensuring this, it will be more difficult for the mold spores to settle, after which they would spread.
Additionally, some growers will promote air circulation by pruning their plants. Techniques of this type include trimming the flower nodes that are inside and the bottom branches.
As for outdoor plants, you can promote air circulation by planting your plants with more space between each other.
Using organic fungicides can ward off the mold that might otherwise attack your cannabis plants. Some natural options include baking soda, burning sulfur, and neem oil. Additionally, you can use a fungicide like Actinovate.
When using these options, alternate between them. This will more effectively protect your plants from potential mold growth.
Monitoring humidity levels can also help you prevent mold growth on your cannabis plants. You can do this in indoor grows with a humidity monitor. Additionally, it can be smart to install a dehumidifier, so you can remove some humidity if the levels end up being too high.
Additional strategies for preventing mold growth include inspecting your cannabis plants every day for mildew or mold signs, maintaining a temperature that’s consistent in your grow room, and cultivating strains that are known for the withstanding of mold.
Also, you can use temporary tarps to protect your plants when there are temporary long rain periods, and when you grow your plants outdoors, you can do so in full sunlight.
If you already have mold growing on your cannabis plant, then you need to use cannabis mold treatment. In this case, a great option is the TRI-OXY COMPLETE. This solution uses ozonated water to get rid of mold and mildew, as well as pesky insects and pathogens.
When removing mold and mildew, you only need to spray the ozonated water on the plants for two minutes to reduce the population significantly. However, when you use this treatment for cannabis mold removal, make sure you do it more than once. This is because you need to regularly spray your plants to kill the mold and mildew and prevent it from growing there again.
In addition to helping you get rid of cannabis mold, there are additional benefits of using the TRI-OXY COMPLETE on your cannabis plants. One of these is that your plants will produce more and grow larger, making your efforts more effective.
Another benefit is reducing the population of insects that try to make your cannabis plants their home. How does this work? You can regularly add in fog ozone gas (the Tri-Oxy FRESH) to destroy the larvae of these insects. Sometimes, this can also kill some of the live insects. As a result, you’ll eventually lower the number of insects in your plants. To do this most effectively, use the intermittent timer that comes with the Tri-Oxy FRESH to discharge the ozone gas at the right time.
Remember that, for safety, you need to make sure you keep pets and people away when you’re using this ozone gas. For indoor water ozonation, the Tri-Oxy® Refresh Ozone Diffuser & Degassing Kit is a companion worth a look.
Now that you’ve learned everything you need about cannabis mold, you might be interested in learning more about the TRI-OXY COMPLETE Solution. Maybe you want to learn more about how ozone works or how to use it on your plants.
The TRI-OXY Complete is one of the best solutions out there for cannabis growers, and it’s also approved and certified safe by the USDA (for organic uses).
To learn more about the TRI-OXY COMPLETE, check out the product now.
Fungus is a stubborn opponent, and I learned that firsthand. Even when I switched from medicines that were antifungals, that are toxic to your body, to natural antifungals, that darn stuff mutates against it all the time. Watching an organism adjust to one remedy after another changes the way you think about keeping it in check.
That frustration is exactly why an oxidative approach appealed to me for grow-room sanitation. I wanted a sanitation step with real strength behind it—one that works alongside whatever program a grower already has in place.
Consistent sanitation is the quiet workhorse of healthy plants, and ozonated water keeps that step simple. The Tri-Oxy® ozone water systems I designed are how I do it.
Look for yellowing or dying leaves near the cola, gray or brown patches that make colas look lifeless, discolored, or limp, and plant tissue that feels dry or crumbles when you touch it. If a bud looks suspicious, break it apart—dark mold hidden inside means bud rot.
Powdery mildew shows up as white, circular spots that look like a light flour dusting, usually on the upper sides of leaves. Leaves may dry out and yellow, and more mature plants can become disfigured as the spread progresses.
Mold favors the same humid, warm conditions cannabis needs to grow, which is why growers are always doing a balancing act. Poor plant health, overwatering, high humidity, and a lack of airflow all contribute.
Promote gentle air circulation, prune interior flower nodes and bottom branches, space outdoor plants apart, alternate organic fungicides such as baking soda, burning sulfur, and neem oil, monitor humidity with a monitor and dehumidifier, inspect plants daily, and cultivate strains known to withstand mold.
Spraying ozonated water on the plants for two minutes can reduce the mold and mildew population significantly. Repeat the treatment regularly so the mold and mildew stay away, and keep pets and people clear whenever ozone gas is discharging.
Yes. The TRI-OXY Complete is approved and certified safe by the USDA for organic uses.
Published December 13, 2021 • Updated August 27, 2026
By Eileen Durfee, inventor of the Tri-Oxy® ozone water systems.
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