Pests In Cannabis Soil: How To Identify And Eliminate Them

You’re casually watering your cannabis plant and notice something strange — a couple of leaves are wilting and the soil looks a bit funny. You bend down to take a closer look at your soil, and to your surprise, you find a few white specs crawling around in the soil and a couple of fruit flies hopping around. 

Spoiler alert: the white specs are probably insect larvae (maggots) and the fruit flies aren’t fruit flies because there are no fruits in a cannabis garden; they are probably fungus gnats. But that’s not the only pest that can infect your cannabis plant’s soil. 

So, why are these pests in your soil, and should you be worried? If yes, what’s the next step for eliminating them? You’ll get all the answers in this article where we dive into why common pests make their way into cannabis soil and how you can deal with them. 

Why Does My Cannabis Soil Have Pests?

Cannabis is no stranger to pests, and as a cannabis grower, you need to prepare your plant against a variety of bugs ranging from spider mites that build webs under the leaves to caterpillars that feast on leaves. 

Such pests are a nuisance and can do a lot of damage to the plant. Some pests suck the sap from the branches, others chew the leaves. These pests cause wounds that can stress out the plant, consume essential nutrients from the plant, and impact various processes including photosynthesis.

But there is a particular kind of insect that’s perhaps worse than this — those that live in the soil. These pests can wreak havoc on your cannabis plant as they consume the roots directly, which stops your cannabis from absorbing necessary nutrients, leading to deficiencies and stunted growth.

Additionally, pests living in cannabis soil can drastically reduce the quality of the soil, and if not fixed on time, they can render the soil infertile for cannabis. They may also invite other pests to the soil, creating further nuisance. 

In some cases, pests in the soil can also give rise to fungus in the rhizosphere, which can quickly turn into slimy roots or root rot, which have the potential to kill your cannabis plant quickly. 

The pests in the soil occur due to various reasons, and they can even occur in indoor cannabis plants. In fact, some indoor plants are more at risk of such pests since they don’t have beneficial insects guarding them, which is usually the case with outdoor cannabis plants. 

How did they get here? Pests can get to your cannabis plant in various ways. If you’re growing an outdoor plant, pests are usually present in the ambient surroundings and can make their way to your plant either by crawling or hitching a ride on other birds and small mammals that may give your plant a visit once in a while. 

On the other hand, indoor cannabis plants can get such pests via open doors or windows or through the vents. Sometimes, these pests can also get on your clothes and shoes, which is why you must change clothes before entering your cannabis grow room.

In some cases, if you have purchased your soil from a random store, it may already be present in the soil in a small population but can quickly grow in numbers over the course of your cannabis plant’s growth — another reason to always choose high-quality soil for your plants. 

What are the Common Pests in Cannabis Soil?

Hundreds of pests can attack your cannabis plant, but those that thrive in the soil are fortunately limited in numbers. More often than not, the pests you see in your plant’s soil are fungus gnats, but they can be other pests, too. Let’s take a look at fungus gnats in detail and go over other pests you may come across. 

1. Fungus Gnats

Fungus gnats are tiny insects that are dark in color and look a lot like fruit flies, and you’ll often see these insects hopping around on the surface of the soil. But unlike other pests, fungus gnats don’t care about your plant’s buds or leaves; their focus is locked on the roots. 

Roots are crucial for your plant’s health, so fungus gnats can be a major problem for cannabis plants. They can claw away the roots within a few days and start affecting your plant’s health drastically.

Plus, fungus gnats reproduce fast. Their life cycle is a month long and an adult female gnat can lay around 300 eggs in her final week, usually on the top of the soil. These eggs hatch and produce larvae that eat root hair and soft root tissue for the first couple of weeks. 

Once they are near their adulthood, they emerge to the surface of the soil to pupate for up to a week. After a week, they turn into adult fungus gnats that live for another week, during which time they start reproducing. 

Fortunately, fungus gnats are usually only a nuisance if your cannabis plant is healthy. A healthy root network can withstand an onslaught of fungus gnats well, but if they grow a lot in numbers or your plant isn’t in the best shape, the infestation can turn nasty. This is why fungus gnats are usually a major risk to seedlings and young plants. 

The funny thing about these guys is that they don’t care what plant you are growing. Whether it is cannabis or tomatoes, they will attack the roots by default. But it’s not like they are on the lookout for roots to hunt; they occur due to two primary reasons. 

Fungus gnats don’t start attacking the roots straightaway, either. They start by eating away the fungus and other organic matter in the soil, and once the soil is devoid of those, they move to the roots, especially root hair and soft tissues. 

Fungus gnats can affect your cannabis plant in various ways, such as the following:

• Yellowing leaves, drooping, spotting, and wilting once the gnats start devouring the roots 
• Symptoms of nutrient deficiencies since the roots can no longer absorb the nutrients well 
• Weakened seedlings that may fall over and eventually die — also known as damping off 
• Stunted plant growth 
• Lower yield than expected 

Fungus gnats are fairly easy to spot in cannabis soil. Yes, they are tiny little insects but are visible to the naked eye. If you suspect fungus gnats in your soil, look closely at the medium and you’ll find some of them hopping around the soil. 

If you see white maggots in your soil, it is also a sign of a fungus gnat infestation. Those little maggots are nothing but gnats in their larvae stage. 

You may also notice other side effects that point to a fungus gnat infestation, including yellowing or drooping leaves, stunted plant growth, or nutrient deficiencies — if these symptoms arise without a clear cause, it’s time to look at the soil. 

To prevent fungus gnats, you should remember a few things. First, let the soil dry out in between waterings. They thrive in moisture, as mentioned earlier, so dry soil can disrupt their life cycle and discourage reproduction. Use soil that drains well to grow cannabis so it doesn’t get waterlogged. 

Also, avoid overwatering. The soil should be moist, but not wet as fungus gnat larvae prefer wet soil. Another reason is if your grow room or ambient climate is humid in general — pests love humidity, it seems. 

You can also place yellow sticky traps near the soil surface since they love the color. The traps will capture adult flying insects and reduce their population. 

As a preventive measure, regularly remove fallen leaves and plant debris from your growing area to maintain cleanliness and discourage gnats. They lay their eggs in decaying matter, so your grow room should be clean to prevent breeding. 

2. Springtails 

Fungus gnats are the most common soil pests for cannabis, but they aren’t the only ones. Another pest that you should look out for is springtails, which is a species of tiny wingless insects that belong to the Collembola order. 

Springtails are no longer than 5-6 mm in length and are usually black, gray, or white in color. They possess three pairs of legs and like to crawl around in the soil and even water trays of hydroponic cannabis. And they can jump really high, hence the name springtails. 

These insects thrive in moist conditions, which is usually the soil used for growing plants like cannabis. Hence, these pests can be a common issue in tropical or humid environments. 

Fortunately, springtails don’t harm cannabis plants directly, but they can still be annoying to deal with. They feed on algae, fungi, and decaying organic matter in the soil, which can sometimes be a good thing, but if their population rises, they can compact the soil and even start eating the roots. 

Plus, springtails often attract other pests to your plant, including mites and thrips, which can lead to other issues for your cannabis plant and its health. 

Since they thrive in humid and damp conditions, it is always a good idea to keep your cannabis room or soil clean and free of decaying organic matter. Leave no treats for them and they will not come. 

3. Root Aphids

Another pest that can sometimes pay a visit to your cannabis plant is root aphids, a small sap-sucking insect that directly attacks the roots. These insects spend most of their life cycle under the soil, which makes them difficult to detect until their infestation has grown to severe levels. 

When these pests attack a plant, they start chewing away the roots, which causes various problems for the plant. Their feasting can lead to slow or stunted growth, yellowing of leaves, symptoms of nutrient deficiencies, and eventually death. 

What makes root aphids worse is not only how difficult they are to detect but how fast they multiply. If they get the right conditions, their population can double in as little as one and a half days!

So, how do you know if your cannabis plant is being attacked by root aphids? Look for honeydew; it’s essentially insect poop that forms sticky residue on the roots, and this also invites other insects and ants to the substrate. 

Additionally, you’ll spot various nutrient deficiency signs without any clear cause like an incorrect nutrient ratio or wrong pH. 

Root aphids are uncommon but a dangerous pest for the cannabis plant. In worse cases, they are almost impossible to eliminate and the best course of action then is to cut your losses and toss your plant in the trash. 

4. Cutworms

If you’ve grown enough cannabis plants, you must have encountered a cutworm or two. As the insects tend to chew their plant stems in such a way that they look like they are cut or make them topple, they are known as cutworms. 

Cutworms are nothing but the larvae of moth species, and are notorious for their tendency to chew through plant stems that are close to the ground. While they love chewing on the base of most plants, they particularly love young seedlings, so you might find your seedlings beheaded at times, thanks to these little monsters. 

Spotting cutworms directly can be challenging since they are primarily active during the night. During the day, they hide in the soil. If you notice that your plant has wilted all of a sudden or has toppled over, it could be due to cutworms. They rarely attack plants with thick stems, but young seedlings and plants are susceptible to them. 

Adult moths that lay eggs on leaves or in the soil near the base of plants are dull in color and come out only during the evenings. The life cycle of cutworms consists of four stages: egg, larva, which is the caterpillar, pupa, and adult. Once the eggs hatch, the hungry larvae or caterpillars start munching on plant material.

If you see that your seedlings are dying suddenly, just till the soil and you’ll be able to spot them. This will help disrupt their pupae in the soil too. One of the best ways to treat cutworms is to spread diatomaceous earth on the soil. The sharp edges can kill these pests effectively. 

Another way is to use Bt (explained below). If you’re growing outdoors, you can also use floating row covers. Create a barrier around the plants to prevent cutworms effectively. Even birds, parasitic wasps, and some types of beetles can help reduce the population of cutworms when you’re growing them outdoors. 

5. Root-knot Nematodes 

Nematodes are small organisms that can either benefit or harm plants. Among these, root-knot nematodes can harm cannabis. These are unsegmented roundworms and measure just a few millimeters in length. They get their name from the knots or galls they cause on plant roots. 

Root-knot nematodes hatch from eggs in the soil. Next, they enter plant roots which causes galls to form. Then, the nematodes feed inside those galls and reproduce, effectively completing their life cycle.

The galls created by these nematodes can affect the root system of your cannabis plant and prevent it from functioning properly. This is because the nematodes snatch nutrients from the cells of the plant which further affects its ability to absorb water and nutrients. Ultimately these plants can experience various nutrient deficiencies and start wilting. 

To prevent root-knot nematodes to a certain extent, avoid using sandy soil as they thrive in it. Although they can affect plants indoors, outdoors plants are more vulnerable to them. These pests love hot temperatures so make sure you maintain the temperatures of your grow room. 

Root-knot nematodes are pretty common in soil and affect a wide range of plant species. In cannabis, though, you’ll see several symptoms ranging from wilted and yellowing leaves to the presence of galls on their roots. Infected plants may also display stunted growth. These pests harm your plants in such a way that they become weak and vulnerable to other pests and diseases, ultimately reducing the quality and yield. 

If you notice that your plants are affected by root-knot nematodes, make sure you treat the soil by heating it. Or, spread the soil out on a tarp on a hot day outdoors. It’s best to get rid of the soil and start anew but you can use it provided all the bugs are dead. 

How to Get Rid of Pests in Cannabis Soil?

Pests can do a lot of damage to cannabis plants, but fortunately, there are several ways of dealing with them. It may seem daunting at first but if you go through the steps properly, you can save your plant while minimizing the damage. 

These solutions are effective against various pests and usually only require basic ingredients that you may already have lying around in your home. Let’s dive in. 

1. Nicotinoid Insecticides

Neonicotinoid insecticides like imidacloprid and dinotefuran are chemicals that are commonly used in agriculture to control pests, particularly root aphids. However, you should use them with caution as they can affect even beneficial organisms in the soil. 

Imidacloprid and dinotefuran are available as granules, liquid drenches, and systemic treatments. Follow the manufacturer’s instructions carefully and use it when the root aphids are still in their nymph or larval phase to prevent them from multiplying. 

2. Bacillus thuringiensis (Bt)

Another effective option for dealing with pests in soil is Bacillus thuringiensis (Bt). It occurs naturally in the soil and is used to treat pest infestations in many crops. Bt produces proteins that kill some pests but are safe for your pets and humans. This biological pesticide is particularly effective against pests that thrive in soil. 

Different strains of Bt target groups of insects, but a subspecies known as kurstaki (Btk) is commonly used for pests like caterpillars, cutworms, and some types of beetles in the soil. 

You'll find Bt available in various formulations including liquid sprays, powders, and granules. Depending on the type of pest you’re dealing with, you can choose any formulation. Regardless of what you choose, though, apply Bt when the pests are still in their larval stage. The larvae must consume the Bt toxin for it to work effectively, so your timing is crucial. 

Typically, growers use Bt as a soil drench or spray to deal with pests in the soil. Follow the instructions provided by the manufacturer to mix it properly and apply it to the soil surrounding the plants. Make sure it distributes well in the soil so it can target most of the larvae. If the infestation is too severe, apply it multiple times for best results; however, make sure you wait for a while before a repeat application. 

Remember that although Bt works great for root aphids, caterpillars, and several other types of pests, they may not be ideal for all pests that dwell in the soil. Therefore, you should identify the pests properly so you can determine whether you should use Bt or not.

3. Hydrogen Peroxide 

Hydrogen peroxide is an excellent solution to common pests living in the soil since this chemical is antiseptic; it disinfects the soil fairly well. Additionally, hydrogen peroxide can also be used for various other plant problems. 

Hydrogen peroxide can come in handy if you want to recycle your growing medium or soil for the next batch of plants. But in this case, we’ll be using hydrogen peroxide as a soil drench to disinfect it from harmful pests and pathogens. 

A hydrogen peroxide solution can not only eliminate insects from the soil but it can also prevent them in the future. This solution can also work if you have pests living on your cannabis plant as opposed to living in the soil. Lastly, it is effective against eggs, too!

Hydrogen peroxide is a naturally occurring compound that turns into water and oxygen once it degrades. It is completely eco-friendly and organic, especially when compared to other synthetic pesticides. However, it is best you don’t use a solution that’s highly concentrated in hydrogen peroxide as it can harm you and the environment. 

You should also keep in mind where you are sourcing your hydrogen peroxide from. When this compound is produced in labs, the process may not be eco-friendly. Some producers of this compound use palladium catalysts, a non-renewable resource. 

But if you source it from the right producer, you don’t have to worry at all. Hydrogen peroxide is even approved for organic agricultural use since it is 100% biodegradable and not a toxic compound. 

Using Hydrogen Peroxide as Soil Drench

Using hydrogen peroxide is fairly easy — all you need to do is dilute it with water and use it as a soil drench. For best results, you should use 3% hydrogen peroxide mixed with water in a ratio of 1:3 (H2O2 to water). 

Ideally, you should use hydrogen peroxide once a week during irrigation. This should be enough for disinfecting the soil and even getting rid of root rot. 

Things to Keep in Mind 

Hydrogen peroxide is a safe and organic compound, but there are a few things you must keep in mind when using it:

• It can sometimes affect the beneficial microbial life within the soil 
• It doesn’t fix the root of the problem, only eliminates the pests 
• Store it in a dark place since it degrades fairly quickly in light 
• It is highly explosive, so do not ever heat it — always treat it with respect — the concentrated form is literally used as rocket fuel. You will probably only have access to 3% H2O2, but still, do not boil it. 
• Always wear rubber gloves when using it since highly concentrated hydrogen peroxide can be dangerous for your skin 

4. Neem Oil 

One of the best and most effective agents against common cannabis pests in soil and otherwise is neem oil. As a grower, you should always have this compound handy. Neem oil has been in use for centuries and there is a reason why it still hasn’t gone obsolete — it’s highly effective. 

Neem oil is nothing but an extract from neem, which is a tree that’s commonly found in South Asia, but it has made its way to various other tropical regions since it is important for farmers around the world. 

Essentially, neem oil makes it difficult for pests to live and reproduce as it hampers their ability to eat and lay eggs. Neem oil is rich in azadirachtin, a compound that hampers pests’ feeding and interferes with their hormones, making it difficult for them to reproduce and lay eggs. 

Additionally, experts believe that this oil also creates a coating layer on insects, which can reduce their breathing abilities. Although neem oil doesn’t necessarily kill pests on contact like other pesticides, it is still effective at eliminating populations of common pests like fungus gnats, mealy bugs, white flies, aphids, spider mites, etc. 

Making Neem Oil at Home

When you purchase neem oil, make sure it is cold-pressed as heat-pressed neem oil lacks azadirachtin. Since pure neem oil is raw and crude, it can’t be used on cannabis plants directly; it must be diluted in water. 

But if you know anything about making cannabis extracts, you’ll know that mixing oil and water isn’t so easy. You need an emulsifier. For this, you can use silica, organic soap, or potassium-based insecticidal souls — just make sure they are non-toxic. 

Once you’ve mixed neem oil with an emulsifier, add the solution to water and mix well. The ratio depends on your preferences, but if it’s your first time making neem oil, stick to a gallon of water, 4 teaspoons of neem oil, and a teaspoon of emulsifier. 

Using Neem Oil to Get Rid of Soil Pests

Once the neem oil is ready, you need to use it as a drench — it should last for 20 days in the soil. Simply drench your cannabis soil in neem oil and let it be. It will start working its magic and the pests will leave your plant alone soon enough.

Do note that if you are using neem oil as a foliar spray, do not use it on buds or seedlings. And only spray it at night. 

5. Diatomaceous Earth 

Diatomaceous earth is an excellent insecticide you can use to kill insects living in the soil. This powder is made from the fossils of a small marine organism called diatom, which existed 30 million years ago. 

This powder is extremely abrasive and physio-absorbent to insects but completely safe for humans and pets. When pests come in contact with it, the sharp blades of the powder pierce and destroy the outer shell of the insects, leading to dehydration and death. 

You can find diatomaceous earth (DE) at any horticultural store. Follow the manufacturer’s recommendations on using it; it’s fairly easy and effective against a variety of pests. 

6. Predatory Bugs

You can also bring some predatory bugs in your grow room that will hunt down these pests. They are cheap to purchase and encourage a diverse microbial life in your garden, which is an added benefit. 

Some of the pests that get rid of fungus gnats include nematodes, rove beetles, hypothesis mites, hunter flies, and synacra paupera. 

How to Prevent Pests from Thriving in Cannabis Soil?

Dealing with pests in your potting soil is relatively easy but what’s easier is preventing them in the first place. Fortunately, it doesn’t take a lot of effort or money to prevent these pests from attacking your cannabis plant. 

Here are some tips that will help you prevent pests in your potting soil:

• Never overwater your cannabis plant; generally, you should only water your plant after the top inch of the soil is dry
• Regularly remove plant debris as it prevents the accumulation of dead matter such as dead leaves, trimmed branches, or any parts of plants showing signs of disease or pest damage. Pests love such environments and thrive in them. When plant material starts decaying it can become a reservoir for pathogens. If you clean regularly, you will disrupt their life cycles by limiting breeding and feeding.
• Excessive humidity caused by decaying plant material can create great conditions for pests and diseases, but it’s bad for the plants. Needless to say, you should maintain appropriate humidity levels and take care of the ventilation to discourage pests. If you live in a highly humid environment, point a small fan at the soil to keep it from getting too moist 
• Check your growing area frequently and look for leaves with any signs of pest infestations. Detecting these issues early on allows you to take action immediately, thereby preventing the pests from proliferating rapidly. Place yellow sticky tapes around your plant to catch pests 
• Maintaining clean tools and equipment. Pests can transfer from one tool to another many times, and the same applies even to diseases. Therefore, it's important to clean and sanitize gardening tools and disinfect your tools between uses, especially when moving between areas or plants.
• If you're using containers for planting, you should also clean and sterilize them before each planting cycle. Any leftover soil or debris in the containers can become a breeding ground for pests and pathogens. 
• Always quarantine and check new plants before introducing them to your garden

Summary: Pests In Cannabis Soil: How To Identify And Eliminate Them 

Unhygienic growing conditions, too much moisture in the soil, and a humid environment are the common reasons why some pests may find their home in your cannabis plant’s soil. And these pests should never be left to thrive. 

Pests like fungus gnats, springtails, and root aphids can create problems by eating away the roots, stealing essential nutrients from the plant, and ruining the quality of the soil. Give them enough time to thrive and they can even kill your cannabis plant. 

Fortunately, they are fairly easy to deal with with the help of hydrogen peroxide, neem oil, diatomaceous earth, and some predatory bugs. And once you deal with them, your job isn’t done — you need to make sure they never come back again.