Sooty Mold: The Causes And Effects On Cannabis Plants 

You enter your cannabis room and your Purple Haze has suddenly developed black spots instead of purple ones — should you be worried? Yes, black spots aren’t a good sign regardless of the cannabis strain you are growing, unless you’re growing black cannabis. In any other case, black spots indicate sooty mold. 

This mold will appear on your cannabis plant in small dark blotches that look kinda furry, and while mold is usually a very dangerous problem for cannabis plants that would have you toss the entire plant in the bin, black mold is a little different. 

It isn’t so harmful, but that doesn’t mean you ignore it. But what is black or sooty mold? Learn everything you need to know about sooty mold in this article, including what causes it, how to fix the problem, eliminate the cause, and prevent it from occurring again in your cannabis garden. 

Black Mold Caused By Pests on Cannabis Plants 

Black mold, actually sooty mold, is a type of mold that develops on cannabis plants, among other plant species, but it is not caused due to a pathogen and it isn’t a disease, either. Instead, this particular type of mold is caused by pests; sooty mold is an umbrella term that describes fungi species that get attracted to pests’ honeydew. 

Cannabis plants have a cellular machinery, which creates sugar within their system through photosynthesis. At the same time, cannabis absorbs nutrients and minerals from the soil via roots, which are transported throughout the plant via the intricate vascular system present within — think of them like veins that are flowing with sugars and minerals. 

While the vascular system is a crucial organ for the plant, it is also quite appetizing for insects. It’s a buffet. Some notorious pests are lucky enough to have piercing mouthparts that allow them to piece the skin of the plant and suck on those nutrients and sugars, which creates many problems for the plant, including nutrient deficiencies, imbalanced growth, infections, etc. 

One such problem that’s caused by such sap-sucking insects is sooty mold. When these insects devour the sap, they defecate, leaving behind a trail. This trail is known as honeydew, which is a botanical word for insect poop. 

Honeydew gets its name thanks to its appearance; it is amber and sticky, and often glistens on the leaves. But don’t dismiss honeydew as just poop — it plays a crucial role in the ecosystem — even honeybees use this honeydew to produce honey. But sometimes, this honeydew can create some problems for your cannabis plants. 

Honeydew is a food source for some varieties of fungal species, which are referred to as sooty mold. Once these spores come in contact with honeydew, they start consuming it and developing into mycelium, which in this case appears black and somewhat fuzzy. This is sooty mold, which may appear harmless at first but it can completely cover the leaves in no time and lead to various other problems as discussed in the following section.

Effects of Black or Sooty Mold on Cannabis Plants

You may have already heard of mold or other fungal diseases cannabis plants may experience, where the mold directly infects the plant tissue. Some of the most common ones include Pythium, powdery mildew, or root rot. However, sooty mold is different as it does not infect the tissue of your cannabis plants directly. 

Sooty mold grows on the surface of the leaves as it expands, following the honeydew trail left by the insects. It isn’t a systemic pathogen like other fungal species, so in that regard, it isn’t as harmful as the rest of them. In most cases, sooty mold isn't a significant threat to your plant. 

If you’re growing outdoors and have a few pesty visitors, sooty mold won’t even grow that far. A few insects aren’t enough to produce adequate honeydew that covers the entire plant, allowing the mold to grow. But sometimes, luck may not be in your favor and sooty mold can get out of hand. 

If the hungry pests don’t have any predators and their population isn’t controlled, they may leave enough honeydew behind for the sooty mold fungus. In such a case, black mold can become a significant problem for your cannabis plant, threatening its health and growth. 

If the black mycelium covers significant portions of the leaves and grows thick enough, it can stop the sunlight from reaching the chlorophyll, which hinders the plant’s energy production. This drop in the photosynthesis process can slow down the plant’s growth, leading to a weaker harvest and subpar yields. 

Mostly, you’ll be dealing with a type of sooty mold that only grows on leaves, but some cannabis plants can develop a more threatening type of sooty mold, which grows on the permanent parts of the plant like the stem or branches. 

Sooty mold isn’t only an issue for your cannabis plants. It’s crucial to know that many people are allergic to sooty mold, so that’s all the more reason to not ignore this “relatively less harmful” mold problem on your cannabis plant. 

Pests That Cause Sooty Mold on Cannabis 

As mentioned earlier, sooty mold is caused by pests’ honeydew. So, it is ideal to treat this problem as more of a pest problem and less of a fungal problem. But before you proceed, you need to learn what kind of pests you might be dealing with when it comes to sooty mold on your cannabis plants. Here are a few common ones. 

1. Aphids

Aphids are one of the most notorious pest species that can attack cannabis plants, and they are usually the reason behind sooty mold on cannabis plants. These pests possess a tiny, soft body, and they are quite common in cannabis gardens. And they have sharp and slender mouthparts that allow them to pierce the plant tissue and suck on the sap. 

Aphids aren’t only naturally designed to consume sap from the plant easily, but they also multiply quickly. So, if you are facing a serious case of sooty mold on your cannabis plant, aphids are more than likely the cause of it. You can also identify aphids through other symptoms like twisted and curled leaves, yellowing leaves, slowed growth, honeydew trails, and wilting of the plant. 

2. Mealybugs

Mealybugs are another species of common cannabis pests and are usually known as perhaps the ugliest of all. These tiny pests look like they are wrapped in cotton, thanks to their waxy white coating. This exterior protects them from natural predators and even some insecticides, making them difficult to eliminate sometimes. 

While they may look small and harmless at first, they are actually quite destructive. They feast on plant matter, making them a significant nuisance for your cannabis plant. If their population isn’t controlled, these pests can cause significant damage to your cannabis plants, including the development of sooty mold on the honeydew they leave behind. 

3. Leafhoppers 

Leafhoppers are common garden pests, about half a centimeter in size and shaped like a wedge. These range from green to brown in color and are part of the cicadellidae family of insects, and like their cousins, they are quite attracted to the sap of your cannabis plants. 

What makes leafhoppers worse than some other pests mentioned here is that they have strong mouthparts that not only help them eat the sap from the leaves but also the stems and buds. Even without sooty mold, a decent-sized leafhopper population can cause reduced vigor in cannabis plants. 

4. Whiteflies 

Not all sap-sucking insects are terrestrial, and whiteflies are one of them — they have wings. These little flies get their names thanks to their tiny white flies, and like mealybugs, even these little pests are covered in a waxy layer. A whitefly infestation can be identified with symptoms like stunted growth, loss of vigor, yellowing of the leaves, wilting leaves, and honeydew. 

Whiteflies pose one more threat apart from sooty mold; they are efficient vectors of viruses, too, that can infect your cannabis plants and wreak all sorts of havoc on them. 

5. Scale Insects

Scale insects appear so unique that you won’t mistake them for other pests. They look like bumps on the stems and leaves of the plant and come in colors like brown, tan, and white. They possess a wax protective shell that covers their bodies, offering them defense.

Like most other pests, scale insects pierce the tissues of cannabis plants with their sharp mouths to feed on the sap, which weakens the plant, leading to wilting and yellowing leaves. Similar to sap insects, scale insects release honeydew, which you’ll find on various parts of the plant like leaves, stems, and buds. This honeydew serves as food for ants that in turn protect the pests. If you see honeydew on your cannabis plants, it’s an indication that there are pests lurking around. 

Sooty mold is caused by the accumulation of honeydew on the plant. Various pests thrive on honeydew, and scale insects are no different. The combined presence of scale insects and sooty mold can have multiple effects on cannabis plants as they block sunlight and hamper photosynthesis, resulting in reduced yields and poor plant health.

Pretty soon, they will start colonizing the surface of cannabis plants, so you need to eradicate them before they completely take over. 

How to Get Rid of Pests That Cause Sooty Mold

Sooty mold may seem like a big concern, but in most cases, it isn’t as devastating as you’d believe — especially when compared to other systemic pathogens that can cause a lot more damage. Nonetheless, letting sooty mold thrive on your plant isn’t something you should allow.

So, how do you solve this problem? You have to take a two-pronged approach — removing the already established mold and eliminating pests in your cannabis garden. It’s pretty straightforward and here are some ways you can do so effectively. 

1. Identify the Pest

The first step is accurately identifying the pest responsible for secreting honeydew, which ultimately leads to sooty mold formation. Common culprits include aphids, whiteflies, scale insects, and mealybugs. It's crucial to identify the pest because treatment methods may differ depending on the type of pest. 

For example, to effectively manage aphids in your garden you can use neem oil, soap water, or introduce ladybugs or lacewings. The same methods that work for aphids also apply to whiteflies, but controlling whiteflies can be more challenging as they are very quick. 

2. Wipe the Plant Down 

The first thing you need to do to fix black mold on your cannabis plant is to wipe it down — it’s simple but it works. All you need to do is wipe down your plant, especially the affected areas. This physically removes the mold from your plant. 

But that doesn’t mean you simply use your old rag; you need to do this in a particular way for the best results. Start by preparing a cleaning solution for this method; take a liter of water, add some natural soap drops into it, and shake well. Then, dip a sponge into the soapy water and wring out any excess fluid. 

Start wiping down your cannabis plant with the sponge, and focus on the affected leaves first. Remember to be gentle; being too harsh can actually damage your plant by causing stress, so don’t apply a lot of pressure. Since the fungus grows on the surface, it will be wiped clean in no time. Continue cleaning until every trace of the fungus is eradicated from your cannabis plant. 

Scale insects require a slightly different approach. The best way to deal with them is by removing them manually where you can scrape or pick them off. Then, you can use neem oil to suffocate the remaining scales.

3. Use Compost Tea 

Sooty mold grows on cannabis plants when it becomes the only species thriving there, eventually gaining dominance of the plant surfaces. You need to avoid this by introducing other beneficial microbes like bacteria and fungi on the surface of your plant, and you can do this with compost tea. 

For this, you need to brew a batch of compost tea at home, which will contain a rich mixture of beneficial microorganisms that won’t allow sooty mold to grow there in the future. You can obviously purchase compost tea from a horticultural store, but making it at home is a lot cheaper (and fun). 

For this, you need an air stone, a small amount of high-quality compost, kelp, fish extract, and humic acid. Follow these steps to brew your own compost tea at home:

1. Fill a bucket with water and let it sit for a day if you’re using tap water, so it loses all the chlorine 
2. Then, add the compost catalyst into the bucket — kelp and fish extract 
3. Add your compost to a sachet — a wire mesh container — and let it sit in the water; think of a catalyst as your tea leaves 
4. Add the air stone to the container to circulate and aerate the water 

After a day, the compost tea will be ready. Ideally, it should appear frothy — the foam indicates nutrients, fungi, bacteria, and nematodes — so it’s a good thing. You can add the compost back to your garden, too. 

Once your compost tea is ready, you need to spray down your cannabis plant with compost tea. This will eradicate any leftover spores from the plant. But don’t spray it at any time of the day; ideally, it’s better to apply compost tea before 10 a.m. or after 3 p.m. so it does not cause burning of the leaves. 

4. Use Neem Oil

Now you have to eliminate the pests, and for this, you can use neem oil. This is one of the best natural insecticides you can use to eradicate pests from cannabis plants, and it has been tried and tested by farmers around the world for decades. 

Neem oil is particularly harmful to pests as it contains azadirachtin, which messes with the hormone systems of the pests, making it harder for them to mature, feed themselves, or breed. The same compound also hampers their sexual communications, so they don’t multiply as fast. 

Another way neem oil is harmful to pests is that it creates a layer of coating on the pests, which stops them from breathing properly. Do note that neem oil does not necessarily kill pests like other insecticides would, but it does push them out of your plants. This makes neem oil effective against various pests like aphids, whiteflies, mealy bugs, fungus gnats, etc. 

Cannabis growers especially love neem oil because it is completely safe and does not harm your plant in any way. However, it is recommended that you don’t spray the buds with this oil as its strong, pungent odor can affect the buds’ flavor profile. Also, remember to mix the neem oil well as you don’t want the oil sitting on the leaves. 

It’s better to prepare neem oil at home as store-bought products may contain other additives or not enough azadirachtin. Follow these steps to make neem oil at home using these steps:

1. Get your hands on 100% raw cold-pressed neem oil — this is because azadirachtin isn’t present in regular neem oil 
2. Get an emulsifier like organic insecticidal soap, potassium soap, or silica
3. Take a gallon of water add a teaspoon of the emulsifier to it and mix well
4. Then, add four teaspoons of neem oil to the mixture and mix well 

For the best results, use neem oil within 8 hours of making it, and do a patch test on a small part of the plant to ensure it does not react to it in a bad way. If all’s good, continue spraying down the entire plant except the buds with neem oil, but do not soak the plant. Avoid spraying neem oil on your cannabis plant if it’s in the last three weeks of flowering.

Keeping Your Plant Safe From Pests 

Whether you have already treated sooty mold on your cannabis plant or merely researched the topic, it’s time to prevent sooty mold from occurring on your cannabis plant. As always, preventing such problems is better than curing them. Follow these steps to prevent harmful pests from taking over your cannabis garden.

1. Use Nets Around Your Plant 

If you are growing cannabis outdoors, it is advisable to use netting as a physical barrier between pests and your cannabis plant. This will stop these sap-sucking pests from making their way onto your plant. Remember to select a fine insect netting that can stop tiny creatures like whiteflies, and don’t worry about air or sunlight — they can still get through and be used up by your cannabis plant. 

If you are growing cannabis indoors, you can use the same netting on the vents so that it filters the air that’s entering your grow room, not allowing any pests to fly in. 

2. Introduce Beneficial Insects

Mother Nature may be your enemy sometimes, but she’s also your best friend when it comes to growing cannabis. So, allow nature to protect your cannabis plant from sap-sucking pests by introducing beneficial insects that will hunt the pests out of your garden. 

Some of the most effective beneficial insects for cannabis plants include ladybugs, ladybirds, green lacewings, praying mantis, assassin bugs, predator mites, spiders, and nematodes. You can either purchase them from your local gardening store or invite them with companion plants like purple dead nettle, dandelion, dill, mint, lavender, and nasturtium.

3. Use Beauveria Bassiana

Also known as BB, this is a biocontrol fungal species that works a lot like BT, which is a bacteria. Beauveria Bassiana infects and colonizes various insect species, including the ones that cause sooty mold on cannabis plants. 

Do note that this fungus can sometimes enter the plant and live there as an endophyte, but there’s nothing to worry about according to some preliminary studies. Research suggests that BB can even work as a natural biostimulant for plants. 

4. Other Precautionary Measures 

Apart from taking the drastic steps mentioned above, you also need to be on your toes on a day-to-day basis while growing cannabis to prevent sap-sucking insects. So, follow these steps, too:

• Keep an eye on your cannabis plant for pests, especially the underside of the leaves 
• Use wide-spectrum organic insecticides when bringing new clones into your cannabis garden 
• Keep your garden well-ventilated since pests don’t like circulating air as it prevents them from mating or laying eggs
• Conduct research and get second opinions while dealing with any pests 
• Don’t enter your grow room directly from outside as pests may be hitching a ride on your clothes 
• Use neem oil occasionally as a preventative measure in your cannabis garden 
• Grow companion plants in your outdoor cannabis garden as they not only attract beneficial pests but also deter harmful pests 
• Maintain the right temperature and relative humidity in your cannabis garden at all times
• Keep your grow room/garden clean and sanitized 
• Always sanitize your tools and equipment after use 
• Use sticky tapes around your growing space to trap any wayward insects 

Follow these steps and you will prevent most pests from making their way into your cannabis garden. 

How to Distinguish Between Mold and Trichomes on the Cannabis Plant?

Sometimes, growers find it difficult to distinguish between mold and trichomes. Here's how you can do that:

1. Location

You’ll usually see glistening trichomes on your buds’ surface, leaves, and stems. You can easily see them without any equipment as they appear like shiny crystals. They have important roles that include protecting the plant from predators and environmental stress.

In contrast, mold tends to grow in concealed areas of the cannabis plant that have less ventilation. Typically, you’ll see mold in buds that are packed tight and other places where moisture can get trapped.

2. Appearance

Trichomes are hairy structures with a round head at the top. Although they appear clear and glassy when young, they may become milky or amber in color when they mature. 

Mold looks more like a webbed structure with irregular patterns. Depending on its type and stage of development, it can be white, gray, green, or even black.

3. Texture

Trichomes feel slightly sticky due to the resin they produce. This resin contains cannabinoids and terpenes. 

Mold has a fuzzy texture and may even feel damp or slimy when touched, thanks to the moisture content. 

4. Smell

Trichomes have a characteristic cannabis smell, depending on the type of strain. If you crush them or take a deep whiff, you’ll see that they can smell skunky, floral, citrusy, or smell like a mango. 

Unlike trichomes, mold tends to give off an unpleasant odor. If you detect this smell, it's an indication that mold is present and should be taken seriously.

5. Density

In terms of density, trichomes tend to be distributed evenly across various parts of the cannabis plant, including buds, leaves and stems.

Mold develops in clusters in certain areas. You’ll see that it’s present only in specific portions of the plant in an inconsistent manner. 

6. Growing Conditions

Trichomes occur naturally and play a major role in the reproductive system of the plant. They are responsible for producing cannabinoids like THC and CBD. They also produce terpenes that are responsible for how the plant smells and tastes. 

Mold doesn’t help the plant in any way. Instead, it ruins the plant and develops primarily because of unfavorable conditions when there is humidity and poor ventilation. It can thrive in areas where air circulation is lacking so it's important to maintain good conditions to prevent mold growth. 

If you’re still confused and find it hard to distinguish between mold and trichomes, you can use a magnifying glass to get a close look. Remember, trichomes will appear like mushroom-shaped heads and will have specific patterns or structures whereas mold will look fuzzy with irregular patterns. 

While trichomes are beneficial and naturally occurring in cannabis plants, the same isn’t true for mold. Consuming cannabis contaminated with mold can lead to health risks, so be cautious and keep an eye on your plants as much as you can. 

Summary: Sooty Mold: The Causes And Effects On Cannabis Plants 

Sooty mold is a result of pest activity in your cannabis garden. When sap-sucking pests like whiteflies and aphids make their way into your garden, they suck the sap of the plant and excrete honeydew. This honeydew attracts and nourishes sooty mold spores, which can turn into a fungal infection really fast. 

However, dealing with sooty mold on cannabis plants is relatively easy. All you need to do is wipe the plant down with organic soapy water, use compost tea as a foliar spray, and neem oil to eradicate the pests. 

In the future, you must prevent sooty mold and sap-sucking pests from making their way into your garden again. You can do this by creating physical barriers between the external air and your plant, introducing beneficial pests into the garden, using BB, and by maintaining basic hygiene in and around your cannabis garden. 

That’s it. Follow this guideline and you won’t have to worry about sooty mold again. To know more about dealing with such problems your plant might face, stay tuned to our blog.