Spider Mites and Cannabis: How to Identify, Eliminate, and Prevent Infestations

You enter your grow room, eager to see your thriving cannabis plants, and you notice something…off. Silky webs adorn the leaves but before you praise their beauty, you realize the scene is straight out of a horror film. 

No, your grow room isn't being decorated by friendly Halloween spiders; instead, these are evil creatures and despite your experience dealing with them, they are enough to make you shiver, especially if your plants are in the flowering stage. 

These tiny pests have taken over your plants like unwanted guests as if they view your house as one giant buffet. Once green and full of life, your leaves are now mottled with yellow spots and it seems like your buds are crying out. 

But don't panic (yet)! This article will equip you with all the information you need on spider mites. We will help you discover them, kick them out of your grow room, and ensure they never return. 

Let's get started!

What Are Spider Mites?

Spider mites are tiny spiders under the Tetranychidae family and although they are named “spider mites”, they aren't true insects despite being related to spiders and ticks. 

Less than 1 millimeter long, it's hard to notice them until they have a thriving population. Depending on the species and life stage, spider mites usually have red, orange, pale yellow, or green oval bodies.

Spider mites are known for spinning delicate threads of silk. The webs are employed to shield their colonies and eggs from predators and environmental threats. Cannabis growers often can't see the silk until it is severely infested.

Spider mites are one of the most infamous nuisances and you'll relate if you're a cannabis grower. They may be tiny and hard to see, but their sap-sucking habit can cause plenty of damage to plants. If you do not take care of it, spider mites can weaken the plants, reduce the yield, and even destroy the whole crop. You must learn about these pests to have optimum plants and yield an amazing harvest.

Spider mites can pose serious problems for growing cannabis for several reasons including:

• Rapid Reproduction

Spider mites can reproduce rapidly, particularly when it's warm and dry. A female can lay hundreds of eggs in her lifetime, which hatch in days and mature. If this keeps on growing exponentially, an infestation can happen in a matter of weeks.

• Plant Damage

These pests suck the juices of the plant by piercing the surface of leaves. The little bug's feeding leaves a yellow or white dot-like speck on the leaf surface — a phenomenon known as stippling. Eventually, the leaves turn yellow, dry up, fall off, and weaken the plant considerably.

• Yield Loss

Spider mites are notorious cannabis pests that affect bud and foliage quality. If a plant is weakened, it cannot put its energy into resinous flowers, meaning lower potency and smaller harvest.

• Resistance to Treatments

Some spider mite populations become resistant to chemical pesticides, making them harder to control. The situation gets worse if the growers rely heavily on one type of treatment. Thus, it's best to rotate between various types of treatments to ensure you're successful. 

• Challenges in Indoor Grows

Spider mites like controlled settings, like indoor grow rooms and greenhouses. The favorable circumstances presented by these environments (warmth, low humidity, and limited air circulation) enhance breeding. So, it can be quite challenging to deal with them in these setups without impacting the fragile equilibrium of the surroundings.

Signs of Spider Mites on Marijuana Plants

Spider mites will often go unnoticed until they cause serious damage. If you can spot them early enough, you can save your plants. Here are a few effective ways to identify them.

• Yellow or white spots on the leaves

Spider mites suck plant sap after piercing the plant surface causing small yellow or white spots to appear on the foliage. You often first notice their presence by the stippling effect.

• Fine Webbing

As infestations continue, you might see fine silky webs on the plants' underside of leaves, between branches, or across parts of the plant. The webs are a protective barrier for the mites and give you a clue.  

• Leaf Discoloration and Wilting

When the leaves of a plant that is infested start turning yellow, browning, curling, and falling off, you know there is a problem.

• Less growth and poor health

If a plant has lots of spider mites in it, the bugs may drain the plant of so much energy that the plant might get stunted. You'll also see that even if it grows, it's way too slow compared to other healthy plants of the same age. Even if you assume that it's a nutrient deficiency and check the pH and everything else to make sure it's in the right range, check the undersides of the leaves first to see if you're missing something. 

• Visible Mites

If you examine carefully (or magnify), you might see tiny, moving dots on the undersides of leaves. These are the spider mites themselves. Depending on the species and their stage of growth, they can be red, orange, or green.

How to Detect Spider Mites on Cannabis Plants

Spider mites are tiny, as you already know. Unless you regularly inspect the undersides of the leaves and look for bite marks, you might miss them and they get away undetected. However, don't worry as there are a few ways to detect them before it's too late: 

• Glasses or Jewelers' Loupe

Use a 10x–30x magnifying glass to inspect the undersurfaces of leaves. You will see spider mites as a dot.

• Sticky Traps

Sticky traps will not trap spider mites mainly but will give you an idea about spider mites when they come wandering.

• White Paper Test

Put a piece of white paper below a suspected leaf and tap it gently. If tiny dots land on the paper and start moving, you may have spider mites.

• Regular Inspections

Get into the habit of looking at your plants at least once a week. Pay special attention to the undersides of leaves, as well as any yellowing foliage.

• Digital Microscope

To take a less manual and more high-tech approach, use a digital microscope and zoom in on potential infestations to confirm spider mites.

When you know the signs and have the right tools, you can catch spider mites early, minimizing damage to your cannabis plants. 

Life Cycle of Spider Mites

If you want to control spider mites, then it is important to know how they live and what they do because if you don't deal with them quickly, they will outnumber you and your plants as they reproduce much faster than you can imagine. In addition, let's explore how to use their life cycle to combat infestations. 

Understanding Their Reproduction Cycle:

Egg Stage

• Female spider mites lay tiny eggs on the undersides of leaves and usually carry an egg sack in their web.
• A female lays only 100-200 eggs and the eggs hatch within three to five days under the right conditions.
• The eggs are so tiny that you will barely notice them. They are often translucent and look like pale white dots.

Larval Stage

When they hatch, the larvae have three pairs of legs (as opposed to the four pairs they will have as adults). At this stage, they start to feed on sap from the plant, although they are less mobile and don't cause as much damage as the adults. 

Nymphal Stages

• Spider mites develop as nymphs in two stages: the protonymph and the deutonymph.
• These phases last just for a few days, in which they grow, molt, and become more active and destructive. Nymphs are little adults with the same anatomy but lighter in color. Think of them as teenagers! 

Adult Stage

• Adult spider mites can move and breed whenever they wish. The male matures faster and immediately seeks a female.
• After becoming adults, females can start to lay eggs 1-2 days after fertilization.
• In warm, dry conditions, the whole life cycle from egg to adult can take just 5-7 days to complete.

As you can guess, even a small population can explode into a massive one simply because of the speed of reproduction, which can be bad news for cannabis growers. But, how can you control spider mites by understanding their life cycle? Here's how: 

• Targeting Eggs and Larvae

It's easier to target the adults rather than the eggs, which means a lot of treatments are ineffective, hence timing is key. But, when you repeat the treatments every 3–5 days, newly hatched larvae are destroyed before they can mature and reproduce.

• Breaking the Reproductive Cycle

Any interruption at one stage of the lifecycle will shock their population. You can use miticides or introduce predatory insects to hinder reproduction.

• Optimal Timing for Treatment

Spider mites breed faster in hot and dry conditions. When the temperature and humidity go lower, the pests don't multiply as much and their growth and reproduction are slow too. 

• Rotating Techniques

If you use the same technique every time, the pests get resistant. To prevent this, alternate treatments like neem oil, insecticidal soaps, and predatory mites. Different methods work at different stages of their lifecycle and are more effective. So, once you understand how they reproduce, you can be strategic and proactive in eradicating spider mites and protecting your cannabis plants.

How Spider Mites Harm Cannabis Plants

Though spider mites aren't easy to spot, they can do some serious damage to your cannabis plants. These sinister pests not only attack the leaves and stems but also the health of the plant, causing problems that can hamper yield and quality. You can get rid of them during the vegetative stage, but pray that they don't invade your plants during the flowering stage as it can be very difficult to get rid of them. 

Let's take a closer look at how spider mites damage cannabis plants and why they are a grower's nightmare.

1. Deformed leaves and stems.

Spider mites use their needle-like mouthparts to pierce the surface of leaves and suck on sap, which contains valuable nutrients and chlorophyll. 

As a result, you may notice dots or specks on leaves. These yellow or white dots increase in size as the infestation becomes severe. Eventually, if you don't take control soon, they may even become larger discolored blotches leading to leaf necrosis. Necrosis is nothing but tissue death so the leaves may turn brown or black and fall. 

When the spider mites feed on the leaves, it lowers the chlorophyll content and restricts the energy production of the plant. Needless to say, the plant ultimately becomes very weak as the leaves start losing their color as well. 

2. Disruption of Photosynthesis

Spider mites severely harm chlorophyll-rich cells. By doing so, they limit the capacity of the plant to conduct photosynthesis.

Naturally, the plant will struggle to grow and may display stunted growth. Of course, the transport of nutrients is also limited. In short, the plant starts declining slowly and will not recover if you don't intervene. 

3. Webbing and Colonization

As spider mites keep increasing in number, these pests weave silky webs to protect themselves and their eggs from predators and environmental conditions. Thanks to these webs, the light will not reach the leaves and further affect photosynthesis. In addition, they can increase the humidity, especially if you have a small grow room, and eventually invite mold and fungi on the buds as well. 

4. Weakening of Stems and Leaves

As spider mites feed on leaves, they curl up, wilt, and eventually drop off. The plant will not be able to survive without leaves. Also, spider mites feed mostly on the leaves but may also attack tender stems that can disrupt nutrient flow and weaken them.

5. Weakened Immune System

When feeding wounds are made in quick succession, it creates openings for pathogens to enter and infect the plant. As a result, they become more susceptible to the attack of fungal diseases like powdery mildew as well as bacteria.

As you can understand, spider mites injure the plant directly but they indirectly invite other problems that can make the plant struggle more. 

6. Reduced Bud Quality

Spider mites redirect the plant's energy from bud production to survival, leading to smaller, less dense buds. Also, it affects the production of trichomes and cannabinoids that reduce the flavor and aroma of the buds, not to mention the potency. 

Don't forget that the buds might get covered in webbing, which makes them unappealing and hard to clean.

7. Lower Yields

When plants get to work with just a bunch of healthy leaves, their system is weakened and the yield naturally decreases a lot. This affects every grower but commercial growers that have invested a lot may lose a lot more. It's a big blow even for home growers as they work in limited spaces and all that hard work is for naught when you don't get the yields you deserve. 

8. Stress-Induced Problems

Spider mites can stress the plants so much that they start becoming hermaphrodites, which means they start producing seeds. When the plant spends its energy producing seeds instead of flowers with rich resin, this lowers the quality of your harvest as most people are interested in sensimilla or seedless buds. 

9. Total Crop Loss

When infestations are particularly severe, the plants may die altogether. As a result, you may not have anything to harvest, unfortunately. Added to that, you'll have to clean and re-establish your grow area to prevent the infection from spreading again. This is very important and you shouldn't skip this. Otherwise, the same story will repeat in the next grow! 

So, if you let spider mites infest your cannabis plants for any amount of time, they will be harder to control and will have a greater impact. 

As you can understand by now, spider mites harm cannabis plants not only in the short term but they can also cause lasting damage that affects the health and yield potential of plants. You must act quickly to detect and eradicate them quickly to keep your plants healthy and productive.

How to Get Rid of Spider Mites 

Spider mites are tough pests to get rid of, but with the proper method, you can get rid of them and protect your cannabis plants! Let's look at the best ways to get rid of spider mites, including organic and chemical methods. 

Organic Solutions

1. Neem Oil

Neem oil is an organic insecticide that affects the feeding and reproductive abilities of spider mites, interrupting their life cycle.

To use it effectively, combine neem oil with water and an emulsifier (like dish soap) and spray it on the affected plants, particularly on the undersides of leaves. However, note that you'll have to use it repeatedly until the pest population starts to reduce. One major con of using neem oil is that you cannot use it during the flowering stage. This is because the buds smell and taste nasty when you spray them with neem oil. If your plants are infested by spider mites during the flowering stage, you'll be better off trying other methods described below. However, if it's during the vegetative stage, use it every 3–5 days over the course of several weeks to reduce spider mites. 

• Beneficial Insects

You can manage spider mites with the introduction of their predatory insects like ladybugs, lacewing larvae, or predatory mites. These enemies of your enemy will eat spider mites on your plants! Let them go directly on the infested plants. And make sure the growing environment is conducive to the insect's survival. 

• Spinosad

Spinosad is a natural product that comes from a soil bacterium. It works very well on spider mites and can be used in organic growing. To use it, spray on the plants covering the leaves and stem. However, alternate other techniques along with this for the pests to be eliminated. 

DIY Solutions

A mixture of water, dish soap, and vegetable oil made at home can kill spider mites and stop their feeding. Apply the solution directly to the affected area every few days.

Chemical Control Options

• Miticides and Pesticides.

When organic measures aren't strong enough, chemical control becomes necessary. Agents like bifenazate and abamectin can rapidly reduce the infestation of spider mites. 

Pick a miticide that is safe for cannabis and follow directions.

• Pyrethrum-Based Products.

Pyrethrum is made from chrysanthemum flowers, and it is a natural insecticide that works on spider mites. Doktor Doom Spider Mite Knockout is a product that contains pyrethrum for an immediate knockdown of mites.

However, use pyrethrum sprays sparingly, and make sure the area is well-ventilated to avoid harming beneficial insects and plants.

• Hydrogen Peroxide Spray (H2O2)

You'll kill spider mites on contact by using a strong hydrogen peroxide solution. To use it, combine one part food-grade hydrogen peroxide (3%) and three parts water.

Make sure to spray the plants completely so that all the leaves, stems and undersides are soaked. However, apply with caution, as overdose can damage plant tissue.

• Systemic Pesticides

Systemic pesticides are taken up by the plant that kills spider mites on contact. Although effective, they should be used sparingly and only when the plants are not flowering. For example, Imidacloprid is an insecticide found in Bayer Advanced Tree and Shrub and other products. To use, follow the manufacturer's directions precisely and apply it as a soil drench or a foliar spray.

• Proper Application Techniques.

When using a pesticide or any chemical control, be certain to cover the tops and bottoms of leaves. Spider mites hide on the bottoms of leaves.

Do not use the same chemical repeatedly to prevent the pests from becoming resistant. Use different kinds of insecticides.

Mechanical and Environmental Controls

• Water Pressure Spraying

A vigorous spray of water can physically knock off spider mites and wash away their webs and eggs. Use this method first before the application of treatments. However, adjust your pressure or you'll end up damaging the plants. 

• Adjusting Temperature and Humidity

Spider mites love it warm and dry. You can slow their reproduction and make conditions less favorable by raising humidity levels to 60–70% and lowering temperatures as well. You can also use humidifiers and fans to control the environment in your grow location. 

Using an alternative organic approach, chemical ones, and modification of the environment can get rid of spider mites from cannabis. To prevent pests in the future, however, a regular check is always crucial before it is done.

Things to Remember: 

• When using strong chemicals, please wear gloves, goggles, and a mask.
• Don't use any type of chemicals on your flowering plants to ensure your buds are not contaminated.
• The only way to be sure that spider mites are completely destroyed is a hard reset and/or using strong chemicals. As you control the infestation, the next step is to do the prevention.

Preventing Spider Mite Infestations

Rather than trying to eliminate spider mites after they have already invaded your plants, the best practice is to prevent them. This way, your plants will be happy and there won't be any threat. You can do this by using some strategies that will not only prevent spider mites but other pests as well. Here's how you can do that: 

• Control the Environment

Spider mites are often found in a dry warm environment. However, if you make them uncomfortable by manipulating the environment as mentioned before, they will not make your garden their home. For this, keep the humidity between 50 to 70% indoors while the temperature should be less than 80°F or 27°C.

In addition, use oscillating fans indoors. Spider mites do not like it when there's wind blowing on them. They are fragile and can drop immediately when you use some strong fans. However, you have to take care not to hurt the plants as too much wind can sometimes break branches. 

• Quarantine New Plants

New plants or clones must be quarantined for at least 2 weeks before being introduced to your grow area. During this time, check for any infestation signs. By doing so, you will keep the rest of your plants safe. 

• Regular Plant Inspections

Whether you want to prevent spider mites or any other common pests that can attack cannabis, it's important to inspect your plants regularly. Do it more when the weather is hot and dry as most pests love these conditions. Check your plants at least twice weekly for spider mites. Make sure you look under the leaves as mites often hide there. 

• Watch out for Warning Signs

Look for little yellow or white spots on leaves (stippling), thin webs on leaves, or the presence of mites (use a magnifying glass to look closely).

Also look in the corners of the grow room, near fans/air vents, and nearby plants for spider mites waiting to hitch a ride!

• Maintain Cleanliness in the Growing Space

First make sure you disinfect the tools, pots, trays, or any other equipment you use to grow cannabis. Sterilize them all regularly using bleach or other disinfectants. In addition, don't reuse soil that may contain eggs or mites.

Most importantly, make sure you remove dead leaves or plant material right away as they attract pests. Keep dust out of your grow room, as it encourages the activity of mites. You can also put a fine mesh filter on your air intake to keep spider mites out if you grow indoors. 

• Using Companion Planting

Companion planting can deter spider mites naturally. Certain plants can keep pests away or attract useful insects that prey on them. Here are a few examples: 

Marigolds: A strong smell that repels spider mites.

Garlic and Onion: Their sulfur compounds repel many different pests.

Dill and cilantro's smells may mask cannabis and confuse cannabis pests.

• Attract Beneficial Insects

Try to plant some alyssum, fennel, or yarrow nearby to attract beneficial predatory insects like ladybugs and lacewings that eat the spider mites. Or, you can purchase some beneficial insects to keep pest populations at bay. 

These measures will make spider mites very unwelcome, while also allowing your plants to flourish. The key is to check the plants regularly and maintain them well to avoid these troublesome pests.

Spider Mites in Hydroponic Grows 

Hydroponics is very efficient in productivity but it doesn't do anything to prevent pest infestations, much like soil. In fact, regardless of the medium you use, you're bound to have pests if you don't take steps to prevent them. However, one advantage of using hydroponic systems is that you don't have to deal with soil-borne pests as it's a soilless way of growing. However, spider mites can attack hydroponic systems as they aren't restricted to soil mediums. 

In fact, spider mites can be a significant problem in hydroponics, so you'll have to do everything possible to prevent them. Otherwise, these mites can take over your entire growing operation and cause more damage than you think. 

Here's how they affect your hydroponic system and what you can do to manage infestations and prevent them from taking place.

• Controlled Environment Attracts Pests.

As mentioned already, spider mites love controlled environments, and what better than a hydroponic system in this regard? The environment of a hydroponic system is reasonably warm and humid for optimal plant growth. Sadly, the same conditions are very conducive to spider mite outbreaks.

Spider mites survive and thrive indoors because they lack natural predators like green lacewings and predatory bugs. So, if you don't control them soon, they can reproduce in an insane manner as there's a lack of natural biological controls. 

• Rapid Spread

Hydroponic plants tend to be grown close together. This is usually done to maximize the space as much as possible. Also, if you're using a drip system, for example, it makes sense to grow them as close as possible. However, this makes it easy for spider mites to move from plant to plant, which means they can easily access your entire crop via air, water, or plant-to-plant contact in hydroponics because, unlike soil where they may be restricted by the soil since it acts like a barrier, there's no barrier here. 

In addition, the plant that you suspect is affected will be compactly inside the grow room, tent, or chamber in hydroponics. When the amount of space is limited, it becomes hard to isolate the infected plant. Also, viruses or other infestations can easily spread from plant to plant. 

• Webbing and Airflow Issues

Spider mites use fine silk-like webs that interfere with airflow and light distribution in hydroponics. As you may know already, proper airflow is important whether it's hydroponics or soil so this isn't limited to hydroponics alone. However, the webs do a fine job of limiting airflow to a great extent. 

Additionally, the webs reduce light penetration although they are fine and silk-like. This, in turn, harms the photosynthesis process and affects the overall plant health.

As a result, when cannabis leaves receive less airflow and light, it causes other stresses to the plant. The damage is much greater than what spider mites would produce on healthy plants.

• Hard to spot infestations early

Growers may believe they are less vulnerable to pests without soil. Thus, they don't inspect their systems as carefully as they would in plants growing in soil. 

For instance, spider mites often hide on the underside of leaves. If you don't check often enough, you might not spot a spider mite invasion until it's severe.

Also, don't forget that hydroponic plants are at bigger risk for damage as they rely entirely on you for their health. Any damage caused by pests will quickly transfer to nutrient uptake issues or stunted growth.

So, be more careful when growing plants in hydroponic systems as a spider mites infestation, even if it's once, can kill your plants pretty soon. 

Summary: Spider Mites and Cannabis: How to Identify, Eliminate, and Prevent Infestations

To sum up, spider mites are common and a strong foe of cannabis plants, but they aren't unbeatable. By monitoring and detecting pests as soon as possible, you can protect your plants from suffering so much. 

To inspect the plants regularly, use tools like a magnifying glass, sticky traps, and a white paper test to catch the infestation early to prevent them from spreading more and more. There are several strategies you can employ to minimize the risk of spider mites invading your grow space, which include keeping the grow room clean, managing humidity and temperature, and quarantining new plants.

However, in a hydroponic setup pest detection becomes a little more challenging. But, you should use the same strategies to eliminate the pests as you would while growing in soil. 

Remember, you can handle spider mites effectively whether you grow in soil or hydroponically. These pests can be eradicated quickly using a combination of organic, mechanical, and chemical means. Ultimately, with some hard work and the right practices, you can ensure that your cannabis plants are strong and healthy without spider mite damage. If you follow all the steps mentioned, you'll never have to see another spider mite again! Good luck and happy growing!