marijuana fungus

Cannabis: Types of Fungi

Fungi are microorganisms that generally live on/off other organisms such as animals, food and many, many kinds of plants. Today we’re going to talk about different types of fungi that can infest cannabis plants and how to get rid of them; keep your plants healthy and stable without losing any of your quality flowers.

Types of Fungi


Oidium is a typical issue when it comes to growing cannabis; a simple excess of humidity in your grow room can cause oidium to rear its ugly head. It looks like a white powder that covers your plants’ leaves along the top in most cases, although in some cases it can be found on the underside of the leaves.

You can get rid of the powder by simply rubbing it off, although it’ll be right back on your plants after just a couple of days. Once it’s on your plants it gets into their cell wall, and it’s impossible to get rid of it fully. You’ll need to treat your plants with fungicide in order to stop the fungi from spreading – try to save as much of your plant as you can, and throw out the part that’s been infected.

Over the last few years this fungi has been found in increasing quantities in outdoor crops, especially in extremely humid areas which need to be sprayed with fungicide if you plan on growing there.


Botrytis is a type of fungi that generally appears on plants that have been attacked by caterpillars which causes holes to appear in the buds. Once the hole has been made, various factors can increase the risk of this fungus such as caterpillar feces, rain water or relative humidity. Buds can easily rot from the inside out, turning quite an ugly brown color, as if it were still wet.

If your plants have become infested you can say goodbye to most of your plants – even if you get rid of all the fungi you can see, the spores have probably gotten to everything. It spreads incredibly fast, even in already-harvested flowers, so when it’s found in one bud the entire branch is usually removed to be safe.

Consuming this fungus is incredibly dangerous for your health – its spores will go straight to your lungs which can cause breathing issues.


Rust is one of the fastest-spreading fungi, as it gets into your plants’ skin and is incredibly easy for your plant to absorb. It shows up as yellow/orange stains on your plants’ leaves, starting on the tops of the leaves which is why sometimes it’s confused with nutrient deficiencies. Once the fungi has taken over your plants, the underside of the leaves will also begin showing red and brown dots, and the rest of the plant will start becoming deformed.


Pythium is a kind of fungi that grows in your plants’ roots, impeding your plants from feeding properly. This fungus essentially weakens your plants’ roots until they eventually kill them completely. It can appear in plants of all ages and sizes, although younger plants are the weakest. Its spores are transported via contact and can even be brought to your plants via the soles of your shoes.

In order to detect this fungus you’ll need to keep a careful eye on your plant, as it’ll cause them to be super weak and show many deficiencies due to the deterioration of its roots. In systems where the roots are exposed such as hydroponics or aeroponics you’ll be able to see them change color to dark brown or even red on occasion.

The best way to fight Pythium is to reinforce Microlife in your plants’ substrate, introducing beneficial fungi that can work together with your roots to protect them and keep them healthy. This can help avoid Pythium rearing its ugly head.


This fungi only ever shows up if your plants haven’t been able to survive Pythium, and it spells the absolute end of your plant. It essentially takes advantage of your plants roots in order to take over the rest of your plant, forming a sort of liquid that covers the roots which stops them from absorbing water and nutrients.

The symptoms are similar to Pythium, although it takes it even one step farther – your plants’ trunk will lose all strength and its leaves will begin drying up and falling off.

Once this fungus is in your plants it’s 100% impossible to get rid of – all you can do is take preventive measures during the growing process and try and keep your plants as healthy as possible, using the beneficial fungi we mentioned earlier.

How to Prevent Fungi

One of the most important factors is how healthy your plants are – the more stressed and unhealthy they are, the more likely they are to become infected by fungi. Healthier plants are a lot less likely to become infected.

Fertilizers rich in silicon reinforce your plants’ structure and cell walls, especially on the leaves, making it much easier for fungi to get to them.

Excessive water can also cause fungi to appear, especially if you haven’t used any clay in your substrate which helps to filter extra water. This tends to happen when people flush out their plants’ roots by watering way too much until the water comes out the bottom. This, plus the fact that it’s your plants’ last few days, makes for a sure-fire recipe for fungi in your plants, especially if their flowers are quite dense.

How to prevent fungi indoors:

You’ll need to use oscillating fans indoors in order to avoid stagnant air which can float in among your plants and easily cause rot and fungi.

During the flowering period you need to make sure that your relative humidity sits under 40%, especially during the few weeks before harvesting which is when your plants are at their most vulnerable and it’s also when it hurts the most to have a mishap. In order to control temperature and humidity, we recommend using a thermos-hygrometer, especially when growing in a grow tent. You can also use a dehumidifier in order to lower humidity.

If your plants do end up getting infected you’ll need to fully disinfect your growing area once you’ve harvested. The next few times you grow in this spot you’ll need to treat them with preventive products and fungicides such as propolis. Keep in mind that mildew spores can stick around for up to two full years before dying off, so you’ll need to protect your plants during that entire time.

How to prevent fungi outdoors:

Some strains are weaker and more susceptible for fungi than others, so you’ll need to plant a strain that’s fungi-resistant if you live somewhere humid. The denser the bud, the more likely it is to become infected. Picking the right strain for your climatic conditions can help you to avoid serious issues down the road.

You will absolutely need to use fungicides and preventive measures when grown outdoors – the last few weeks, outdoor plants generally coincide with low temperatures and high humidity, which is why it’s much more dangerous and it can end up ruining a lot of hard work.

In this article we're going to explain the types of fungi that can infect cannabis plants and the best way to get rid of them.

PSA: Check Your Cannabis for Mold

Spotting mold on bread or cheese is pretty easy, but on cannabis? Not so much.

Here’s everything you need to know about what to look for, whether it’s safe to smoke moldy cannabis, and how to keep your stash mold-free going forward.

Moldy cannabis usually has a grayish-white coating. If you’re not a seasoned consumer or grower, though, it can be easy to mistake trichomes for mold and vice versa.

Trichomes are those sticky, shiny crystals on the leaves and buds that give cannabis its aroma.

Unlike trichomes, which look like little hairs that almost appear to glitter, mold has a gray or white powdery appearance.

Mold also has a distinct odor to it, so your nose may notice the mold before your eyes do. Moldy weed usually has a musty or mildewy smell, or it may smell kind of like hay.

It probably won’t kill you, but it’s still not recommended.

In healthy people, smoking moldy weed isn’t likely to have a detrimental impact on your health — barring the general risks of smoking, of course.

If you smoke moldy weed, you might experience symptoms like coughing, nausea, and vomiting, which are more unpleasant than dangerous.

But if you’re allergic to mold, you could end up with inflammation of your sinuses or lungs and symptoms like:

  • sinus pain
  • drainage
  • congestion
  • wheezing

In people with weakened immune systems or lung conditions, inhaling smoke from weed that contains certain mold species can have serious health consequences.

Fungi like Aspergillus, Mucor, and Cryptococcus can cause serious and even deadly infections in the lungs, central nervous system (CNS), and the brain in people with compromised immune systems.

A UC Davis study found these and other types of potentially harmful fungi on cannabis samples bought from dispensaries and growers in Northern California.

You may be tempted to cut off the obviously moldy bits and smoke the rest, but it’s not a good idea. Life’s too short for bad bud.

If you can see mold or mildew, you’re better off tossing it. It’s not going to taste or smell good anyway, and could make you feel sick.

Storage is everything when it comes to preventing mold.

Exposing cannabis to the wrong temperature, light, humidity, and oxygen can promote the growth of mold.

Here’s what you need to keep in mind.

Avoid the fridge or freezer

Forget what you’ve been told about storing your green in the fridge or freezer. The temperatures are too low, and the exposure to moisture can result in mold.

The ideal temperature to store cannabis is just below 77°F (25°C).

Use the right container

Glass jars with an airtight seal are the way to go if you want to keep things mold-free.

Mason jars and similar glass containers help limit the exposure to oxygen and moisture, which can prevent mold and keep your nugs fresh longer.

If you want something a little more sophisticated than a Mason jar, most dispensaries sell containers designed for this exact purpose.

Keep it in a dark, dry place

Direct sunlight and moisture are recipes for disaster when it comes to keeping cannabis fresh.

The sun’s rays can heat things up and hold in moisture. A damp environment can also cause too much moisture to build up if your container isn’t properly sealed.

Keep your container in a dark, dry cabinet or closet that doesn’t get too hot.

Mind the humidity

Cannabis is best kept at a relative humidity of 59 to 63 percent. Go any higher and you run the risk of trapping moisture and growing mold.

Adding a humidity pack to your container can help. These are little packets that contain a mix of salts and water that help regulate the humidity in your container. They’re inexpensive and last a couple of months.

Humidors made specifically for cannabis are another option if you want to get fancy and are willing to spend some extra bucks.

Like most green things, cannabis can develop mold under the right conditions. Learn what to look for and whether there's any way to salvage your bud.