How to Avoid and Spot Moldy Weed

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Moldy weed
Author avatar By Derek LaRose
March 11, 2022
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It’s perfectly normal to see critters crawling around on your plants, but they aren’t the only living organism that likes to take a bite from your marijuana. There’s something else that sees your cannabis as the ideal snack. Yes. We’re talking about mold on weed

You might be used to spotting a moldy piece of bread or some furry green fluff on your cheese, but what does it look like on your marijuana plant? Can weed get moldy? Does it do a lot of damage? What would happen if you smoked weed mold? 

Fear not! Marijuana mold is widespread, and you’re likely to encounter it during your growing endeavors. We’re here to answer all your questions and give you the lowdown on three types of fungus you might encounter, how to tell if weed is moldy, and how to combat the stuff. 

Are you ready to attack your moldy weed and maintain healthier plants? Read on!

Weed with mold
Weed with mold

What is cannabis mold?

When you think of the word ‘mold,’ your mind likely conjures up images of rotting food and something you left at the back of the fridge for too long. Not nice, right? Mold on pot plants might not look attractive when it nibbles away at your pretty leaves, but it plays a fundamental role in nature

This fungus works by forming a dense mass of fibers called mycelium. Molds don’t have a digestive system. Instead, they put out enzymes to break down substances, including plant matter and wood. They’re known as nature’s great decomposers as they destroy waste, dead animals, and plant matter into tiny particles to return to the soil, which we know as the circle of life. The mold on your weed is doing just this.  

What does moldy weed look like? Fungus on your plants isn’t as apparent as it is on food, but if you know what to look for, it’s easy to spot. The mold tends to have a grayish-white coating

If you’re not an experienced consumer or grower, you might get confused. You’ll need to understand if you’re dealing with trichomes vs. mold. The former is the shiny, sticky crystals on leaves and buds and gives marijuana that delightful, infamous aroma.

When you look closely, you’ll notice that trichomes appear like tiny hairs that glitter, whereas white mold on weed looks powdery. Fungus gives off a musty or mildew smell, which can give it away if you can’t tell otherwise. 

The 3 different types of mold on weed

If you’re unsure what you’re dealing with and still need an answer to the question, ‘what does mold on weed look like?’ We’ve put together a description of the three different varieties you can expect to pop up on your plants

Understanding basic knowledge about each type of moldy weed can help keep your precious cannabis safe. Ensure you get familiar with the traits, signs, and symptoms to help treat and prevent them in the future. After all, the only one trying your marijuana should be you!

Be extra careful if your indoor cannabis humidity levels are high, as this provides the perfect environment for any mold.

Bud rot

This grey mold, aka botrytis, usually gets into your plants through openings and wounds. Nothing is safe from bud rot, though, and even healthy plants are at risk. This fungus is difficult to avoid as it spreads through airborne transmission and is almost always existent in the air. 

When bud rot enters an opening, its spores can spread rapidly, which has the potential to infect a whole plant and even its neighbors. 

What to look for:

  • Small, black mold on weed in dot formations
  • Large, fuzzy grey areas
  • Buds and leaves shrivel, turn brown, and die
  • Leaf tips go from green to yellow to brown

White powdery mildew

Despite there being one collective name, a variety of powdery mildew exist. It doesn’t matter the species as they all create a fine dust-like layer on the foliage. Your knowledge of powdery mildew vs. trichomes is crucial here in understanding whether you have an issue or not. 

The infection begins as small patches and then spreads into larger areas on lower leaves. Over time, the fungus expands to branches, stems, and even flowers. If an infection reaches advanced stages, the mold produces spores on the most compromised leaves.

What to look for:

  • White, powdery patches on fan leaves
  • Stunted growth and distorted leaves
  • Discolored plant tissue
  • New leaves and flowers look infected
White powdery mildew on marijuana plant
White powdery mildew on marijuana plant

Sooty mold

If you spot black mold on weed, it could be the sooty variety. This fungus creates a dark, flaky powder on leaves that looks like it belongs to a chimney sweep, hence the name. The black dust is easy to spot, and you can treat it quickly. 

The small black patches begin to spread until they cover the surface of fan leaves. Sooty mold on weed disrupts photosynthesis, impeding your plant’s growth

What to look for:

  • Black’ soot’ on leaves
  • Aphids, leafhoppers, and whiteflies on your plant

Encountering moldy weed at different grow stages

Throughout your plant’s life, there’s always the chance that marijuana mold will come creeping. Even if you make it through every stage, you’re most likely to get attacked in the last two weeks before harvest, which can damage your entire crop.  

A last-minute invasion is very frustrating, especially when you know that smoking moldy weed can do you harm. Never roll a joint with buds that look fuzzy white, brown, black, or gray. If you do, you risk the following unpleasant symptoms:

  • Coughing
  • Nausea
  • Vomiting
  • Sinus pain
  • Congestion
  • Wheezing

The best thing you can do to help your beloved plants is know how to tell if weed is moldy at different growth stages

Vegetative stage

During the vegetative stage of your plant’s life, white powdery mildew is the most likely to appear. Your cannabis will be enjoying spreading its leaves that create a hot and humid environment. These conditions pave the way to white mold on weed. This fungus finds its way to your leaves, buds, and stems

Your leaves will look like someone threw flour on them, which is a bad sign. Let it get out of control, and this pesky mold will destroy buds and possibly the entire plant

Keep your eye on your marijuana during this stage, especially if you’re growing indoors. When plants get big in small spaces, there’s less airflow, which can form pockets of stagnant air, leading to, you guessed it, moldy weed.

Flowering stage

Can cannabis mold during the flowering stage? It sure can. This period is a very susceptible time for your weed, and your plant is prone to the white fuzzy mold and the dark brown or dusty gray kind. Sadly, the bigger and denser your buds are, the easier it is for an invasion to occur. 

Whatever type of mold infects your buds, they all have the same effect; bud rot takes hold inside the flower without you knowing. You’ll think everything is going well until the leaves suddenly die on you. Soon after, the bud will discolor, and you’ll know mold is taking over.

When bud rot strikes, you need to act fast and cut down all affected flowers and trash them. Your best bet is to harvest the plant immediately because an infection can spread rapidly and damage your whole crop overnight. 

Trichomes or mold?

If you notice white mold on buds, you’ll have to decipher whether it’s trichomes or mold. Trichomes should be there and are what gives your marijuana its delightful smell. Mold, on the other hand, needs to be taken care of. 

Remember that trichomes look like tiny hairs or crystals, whereas mold tends to look powdery. To make sure you don’t make any mistakes, a magnifying glass is your best friend. Imagine harvesting early because you thought there was mold on your plant, only to find it was trichomes!

Drying and curing

You’ve worked extremely hard up til now and harvested some beautiful-looking buds. Don’t let your guard down yet. Your drying and curing method plays a massive role in your weed’s potency, appearance, and taste. Turning a blind eye to moldy weed now could be a fatal error.

When you dry and cure your weed the right way, you prevent mold. Without knowing it, you can easily create an environment ideal for the fungus to form, so don’t skip any steps. Make sure you check your buds frequently to react quickly if a problem arises.  

Moldy cannabis
Moldy cannabis

How to treat and prevent mold on pot plants

Ideally, you want to prevent mold before you have to deal with the problem. Depending on if you’re growing weed indoors or outdoors, there are a few techniques you can apply to ensure your plant has the healthiest life possible.

Indoor weed mold prevention

If you’re an indoor weed grower, you’ll need to create the perfect environment from the get-go. Keep humidity relatively low and set up an exhaust system. Consider these tips to prevent cannabis mold inside.

  • Place fans around the growing space so your plants get air from above and below to prevent stagnant air.
  • Stay on top of pruning and trimming by being aware of overall plant mass. The more leaves there is, the more moisture.
  • Invest in a quality humidity monitor and check it regularly.
  • Do a quality check often to inspect buds and act quickly if you see any signs of moldy weed.
  • Don’t let the environment get too hot or cold.
  • Grow strains renowned for withstanding mold. Great indoor options include Moby Dick and Sweet Tooth.
  • If you get mold on weed, it’s best to harvest the plant as soon as possible. The longer your infected cannabis stays among the crop, the more mold spores will be in the air meaning other plants will get infected.

Outdoor weed mold prevention

Growing weed outdoors makes it a little easier to prevent mold on pot plants as they’ll have more access to natural airflow. You can help them further with these techniques.

  • Shake your plants every morning to get rid of dew and after every rainfall. Wet buds are a breeding ground for fungus, so you need to avoid them as much as possible. 
  • Plant in a spot where there’s lots of breeze and sunlight to help keep leaves dry. 
  • Protect your weed as much as possible from wet and cold climates. 
  • Plant cannabis in portable containers so you can move during bad weather. 
  • Space your weed out, so no plants are touching.
  • Grow resistant strains for the outdoors, which could be Frisian Dew or Jamaican Pearl.
  • If the weather is too cool or wet, harvest immediately. These conditions are prime for cannabis mold and bud rot, and once one plant gets infected, it can spread rapidly. 
Healthy cannabis flower
Healthy cannabis flower

Prevent moldy weed and keep your plants healthy

Marijuana mold will look and smell off, making it easy to spot. As long as you perform regular checks on your plants and create the right environment, you should be able to prevent a majority of fungus from attacking your cannabis. 

Knowing how to tell if weed is moldy is essential so that in the unfortunate event that an infection does take over, you can act fast. Check out our other articles to know how to keep your cannabis healthy and grow the best weed.


About the author: Derek LaRose

Also known as Kronic from The Cannabis Kronicles, Derek LaRose is a young ambitious cultivator and a staple educator for indoor cultivation.

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