Everything You Need To Know About Bud Rot & White Powdery Mildew On Cannabis Plants

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Added 13 October 2021

Many things can go wrong for cannabis growers as they approach the final few weeks of flowering. From pest invasion to nutrient deficiencies, several problems can lower your yields. 

While you can correct most of these issues, it gets difficult to get rid of mold once it starts spreading. So the only way to protect your plants is to prevent mold in the first place because once it takes over, it quickly spreads to the rest of the grow room. And, before you know it, you've got moldy buds that are not only dangerous to ingest but can also kill other plants.

In this article, we will explore why mold is so dangerous and how you can prevent it.

What is Mold?


Mold is nothing but a fungus that can affect a cannabis plant at any stage of its growth, including the vegetative, flowering, drying, and curing stage! It's perhaps the most dangerous of all problems growers face because it renders the buds useless.

Many people ask if it’s okay to remove the mold from buds and use them. No. Do not ever ingest or smoke moldy buds. Smoking moldy buds can be dangerous for your lung health. Moreover, diseased buds never taste good. Instead of tasting the strain’s characteristic flavor, you will have a sour taste in the mouth. 

Types of Mold

Technically speaking, two types of mold can quickly problematic if you don’t address them:

1) Bud Rot or Botrytis

2) White Powdery Mildew (WPM)

Bud Rot 


Bud Rot begins developing in the center of the buds. Since it starts at the core and then spreads towards the outer parts of the bud, it's tough to catch it early. Typically, it affects the plant during the flowering stages. Unfortunately, Botrytis can destroy an entire grow room within a week once it spreads, which is why you should be stubborn about preventing it at all costs. 

Botrytis systematically breaks the buds down and releases spores that impact all neighboring plants. It appears wispy and white during the initial stages but turns gray and then black if you don't take action. The buds may also seem slimy to the touch.

It's a good idea to get rid of the bud in the initial stages as soon as you see white mold. If the buds are badly affected, the best solution is to cut off the infected stems and let the plant grow as usual.

Since bud rot sets in due to extra moisture, it may still be possible to salvage the remaining buds. However, if the entire plant is hit, you may want to discard it and inspect every neighboring plant to catch it early.

In outdoor grows, the plant gets affected during and after rainfall. Mold is usually easy to spot in cured buds as you break or grind them. Sometimes, it's possible to detect Bud Rot with just how the buds smell — musty, old, and damp. 

White Powdery Mildew


As the name implies, White Powdery Mildew is a type of mold that appears as a powdery white substance on the plant. However, unlike bud rot, WPM is visible, making it easy to detect it in the early stages. WPM attacks the plants during their growing and flowering stages and starts in the lower parts of the plant before spreading to the upper parts.

WPM may also look like trichomes, but the main difference is that WPM feels and looks like powder while trichomes are gooey and resinous. Once WPM attacks the plant, it can rapidly spread to other parts if you don't stop it in time. This mold will usually attack vulnerable plants and will also thrive in areas with less or no ventilation.

Another type of mold that can affect your plants is Downy Mildew. Many people confuse Downy Mildew with WPM, but they are not the same. Unlike WPM that likes hot weather, DM loves humid and colder temps. On the other hand, it’s very similar to Botrytis because it can appear bluish and gray at times. 

The symptoms first develop on the undersides of the leaves with blue and white spots. It can also look fuzzy, indicating the presence of mold. If untreated, the spots can spread to other parts of the plant and kill it eventually.

How to Prevent Bud Rot?

Bud Rot or mold is fungi that thrive in specific environments that are conducive to its survival. A few factors that encourage Botrytis includes:

1) Thick buds and leaves

2) High humidity

3) Poor airflow

4) Vulnerable plants

5) High temperatures

Many growers invest in Sativa strains with airy leaves and buds to prevent bud rot. How? Well, Sativas grow lean and tall, and the mold has very few chances to spread in areas with lots of airflow. In contrast, Indica plants are bushy and produce dense buds that are simply perfect for mold and fungi.

Another effective way to prevent Bud Rot is to reduce humidity and maintain it at low levels using a dehumidifier. Since buds develop more resin in dry environments, it's a win-win for the grower.

In addition, keep the temperatures as low as possible to keep the mold from spreading. Using a fungicide during the vegetative stage may also help as a preventive measure. Since you need to maintain both humidity and temperature levels, an air conditioner is a better option. 

Bud Rot is not really hard to destroy. It's just the amount of spores that make it difficult to manage. Unlike Root Rot that's pretty much impossible to cure, you can manage Bud Rot if you're quick.

In addition, Bud Rot rarely affects healthy plants. Instead, it goes after susceptible plants in wet grow rooms with high humidity levels above 90%. So, how do you prevent humidity from increasing? First, install small fans that helps all the excess water dry up. Some growers ignore ventilation and just install an air conditioner. However, fans are more critical because it encourages airflow.  

Next, make sure you do not overwater the plants. If the water is collecting in puddles after watering, there's a problem with the water drainage. Bud Rot generally attacks plants through pests. If you keep pests at bay, you're automatically avoiding bud rot.

Finally, if the bud rot has advanced to uncontrollable levels, you will have to eliminate the plant before it infects all the plants in the grow room. Ensure that you don't leave any diseased material like dead leaves behind. Clean and disinfect the grow room after removing the plants so it's safe for future projects.

How to Prevent White Powdery Mildew?

White Powdery Mildew is similar to Bud Rot in terms of the conditions required to spread. So, you can take the same preventive measures used for Bud Rot. From selecting the correct type of seeds to installing air conditioners, dehumidifiers and fans, follow the same procedure used to prevent Bud Rot.

WPM is slightly more forgiving than Bud Rot; however, if you're late to take action, the results are pretty much the same because WPM also spreads just as fast as any other mold.

WPM is an airborne pathogen that spreads through spores in the air. Keep the grow room sealed at all times and ensure that you don't allow pets inside the grow room. In addition, other growers cultivating cannabis plants may also bring in outdoor spores, so do not allow anybody else to enter your grow room.

The first signs of WPM start with a powdery substance accumulating on the undersides of the leaves. Your best bet to beat it would be to catch the early signs and defoliate all sick leaves.

Another way to prevent mold is by pruning the plants frequently to ensure that there’s a lot of room around the plants. Also known as defoliation, pruning is great for your plants because it forces them to grow back stronger. 

If you’re wondering whether it adversely affects the plants, just remember that it’s also a way to train the plants to become stronger. The basic idea is to prevent a dense structure, so the mold cannot attack the plants.

Next, always make sure that the grow room is clean. This sounds obvious, but most people don't realize that unclean grow rooms only invite pests and diseases. As debris collects in the grow room, pests, and mold latch on to them only to invade the plants later. Therefore, cleaning the grow room after every harvest is best to prevent mold spores.

If the plants have suffered due to WPM or mold of any kind, it becomes even more important to clean the grow room thoroughly. First, make a bleach and water solution by mixing equal parts of bleach and water. Next, spray it all over the room and let it dry. Make sure you get every little corner because mold tends to collect in small damp spaces. Cleaning with either bleach or hydrogen peroxide will also keep pests at bay.

Since grow rooms generally remain damp due to watering and spraying the plants, it becomes very tough to keep mold at bay. You may try all the tricks in the book and still have mold or bud rot due to factors that are not in your control. Although installing a powerful air conditioner is enough to control humidity, you may need to install an air purifier if you're constantly struggling with mold.

Spending money on an air purifier may seem too much for a home grow, but consider it the last option if nothing works. Commercial operations set up air purifiers that destroy mold spores and other air pathogens because mold can quickly spoil their crop during the drying stage.


Rather than using fungicides at the last moment, use preventive measures to control mold. As long as you keep the humidity and temperature low, you have nothing to worry about. Both Bud Rot and WPM are forms of fungi that spread through spores in the air. Therefore, it’s important to keep the grow room dry and position the plants a little far away from each other. 


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Good and informative story! Also, I like the clean layout and nice images!