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Most Common Pests In Cannabis: Spider Mites

Spider mites are tiny spiders, they're the very common in cannabis and their webbing can be a growers worst nightmare.
22 April 2022
8 min read
Most Common Pests In Cannabis: Spider Mites

Contents:
  • 1. What are spider mites?
  • 2. What do spider mites look like?
  • 3. Where are they found?
  • 4. What do spider mites do?
  • 5. Spider mites symptoms
  • 6. How to prevent them?
  • 7. How to deal with them?
  • 7. a. Environmental factors to keep in mind
  • 7. b. Regular pruning
  • 7. c. Hosing the crop regularly
  • 7. d. Beneficial insects
  • 7. e. Organic pesticides and essential oils
  • 8. In conclusion

Spider mites are the most common pest in cannabis. These bugs live in dirty indoor and outdoor grow spaces where they feed on chlorophyll and sap, webbing all over your precious plants.

1. What Are Spider Mites?

Spider mites are common in cannabis, these small mites hide inside the buds, sucking the liquid in your plants and leaving webs all over. It's fairly easy to eliminate them but make sure you spot them early because they can rot the buds, ruining your entire harvest really fast. These tiny mites are related to spiders, ticks,  and other small Tetranychidae. They are a very common bug that attacks cannabis, seeking dark places in plants where they can lay eggs and continue to reproduce.

2. What Do Spider Mites Look Like?

These bugs are actually super tiny (around 0.5mm). They can be red or black and have 8 legs.

 

Most Common Pests In Cannabis: Red Spider Mite

Red spider mite.
 

Because they’re so tiny, you’ll only be able to see tiny dots walking around your plant unless you have a 10x microscope available.

3. Where Are They Found?

Spider mites can be found walking all over the plant but you’ll usually find them on the underside of the fan leaves. That’s where they lay their eggs, protecting them from the sun and other elements that may affect them.

4. What Do Spider Mites Do?

These mites feed not only on sap but also on chlorophyll, damaging the plant. Even though this can have a toll on your plant, this is not the worst they can do. Spider mites can reproduce super fast and will use their web to protect their eggs. This means they will completely cover your plant in spider web if you don’t deal with them early. They can even lay eggs inside the buds and when the eggs hatch, they will start eating the inside of your bud, causing bud rot.

 

Most Common Pests In Cannabis: Spider Mite Bites on Cannabis Leaf

Spider mites feed not only on sap but also on chlorophyll, damaging the leaves.
 

Even though the webbing won’t kill your plant, it will be impossible to remove it if you’re in the flowering stage as it can get stuck in the flowers. So although it doesn’t kill your plant, you will have to throw it away if you get seriously infested when flowering.

5. Spider Mites Symptoms

The symptoms you’ll see with spider mites are just signs of their presence. The first thing you see is tiny yellow or white spots, these are mites' bite marks and they are a sign that they are feeding on your plant. After that, you will start to see small transparent eggs stuck under the stems and leaves, this is a sign that the infestation is starting to grow.

 

Most Common Pests In Cannabis: Spider mites infestation

Spider mite infestation during the preflowering stage.
 

If left untreated for around a week, you’ll see what they can do. You will start to see webbing all around your plant and you’ll be able to see the mites walking all over your plant.

6. How To Prevent Them?

Although like with other pests like Mealy bugs, there is nothing you can do to avoid them 100% other than keeping a good growing environment. Keeping your growing space clean and quarantine clones (or other plants) before bringing them in with your plants is a good way to prevent them. Because spider mites don’t like wind, keeping a well-ventilated growing room can be an effective way to prevent them also. If you want to do everything you can to prevent them, you could slightly spray insecticides to prevent their appearance but this can affect your plant. But the best way really is to keep your space clean, with the appropriate temperature, humidity and ventilation.

7. How To Deal With Them?

If spotted in the early stages, it can be fairly easy to remove the eggs manually or with a high-pressure sprayer to knock them down. After you remove the excess, you can apply Neem oil or a mix of alcohol and water to eliminate the rest. Now if your plant is being taken over, it can be difficult, because they can cause bud rot and can hide inside the buds.

 

Most Common Pests In Cannabis: Neem Oil against Spider mites

After knocking them down, Neem oil is a good way to deal with spider mites.
 

You will have to make the hard decision of completely eliminating them by applying harsher chemical products, with the risk of damaging your plant or applying organic and safer-to-use insecticides daily, with the risk of losing your plant to spider mites. If your plant is severely affected, the best thing to do is throw the plant out to avoid them spreading to your other plants. Spider mites are infamously good at quickly developing a natural resistance to many of the common pesticides used, and these pesticides can also have a harmful effect on other beneficial insects that gobble up spider mites. Not worry though, as there are some ways you can improve your chances of infestation prevention and control. By controlling the growing environment, regularly pruning your cannabis plants, and hosing your plants you will decrease the likelihood of spider mites (and other bugs) ever affecting your crop.

Environmental Factors to Keep in Mind

Spider mites are notorious for loving dry and hot conditions. They thrive in temps above 22ºC, which is also unfortunately in the perfect temp range for growing cannabis. Before you try to use any pesticide measure against spider mite, try bringing the grow room temp down to below 20ºC and keep it there for 2 to 3 days. Keep a close eye on your plants to make sure they are dealing with the lower temps.

Female spider mites can lay up to 100 eggs during their 70-odd day lifespan. These eggs can take anywhere between 3 to 19 days to hatch, depending on the room temperature. The lower the temperature, the slower the gestation period will be, and the more time you will have to deal with any unhatched eggs. It is a good idea to also create some extra airflow within the grow space, as spider mites hate windy conditions and will lay eggs less frequently if there is optimal airflow throughout the canopy.

Regular Pruning

Regularly pruning the older fan leaves from your weed plants can go a long way in preventing infestations from getting off the ground, and also stopping the spread of any small infestations. There are multiple pruning methods that growers implement to help with nutrient distribution, and all of these methods will help with removing areas for spider mites to lay their eggs. If you are already dealing with a small infestation, check your whole crop top to toe. Remove each and every site where you see any signs of infestation. Don't worry about removing too much plant material, as it is in the plant's best interests to banish the mites totally. 

If your crop is showing signs of a large-scale infestation then you may have to consider sacrificing the infected plants to save the healthy ones. Spider mite infestations can spread quicker than wildfire, and once a big infestation has taken hold it can be extremely difficult to control it. What's better, a couple of healthy plants making it to harvest, or a full crop of infested plants that do not reach their potential and maybe so badly infested that you cannot enjoy the buds either way?

Hosing the Crop Regularly

Hosing your crop is another way to help prevent infestations and also slow the rate of spread if there are spider mites present. You can hose them down with regular tap water but in general, it's a good idea to grab a sprayer bottle from the closest garden store and use water that has been pH balanced

Washing your plants like this will help remove any active spider mites, and also dislodge the unhatched eggs that will inevitably be hiding somewhere. Hosing can be done as often as you see fit, but if your crop is in the later stages of the flowering cycle be careful with the bud sites. 

Many cannabis cultivators like to use a mixture of water and alcohol to spray the plants. Any rubbing alcohol will do, and you want to make the mixture with a ratio of 9 parts water 1 part alcohol. This mixture will kill the mites and eggs pretty quickly, while the plant itself will remain unaffected. 

Beneficial Insects

There are a bunch of insects you can add to a grow room that love to eat spider mites, and other nasty bugs. They do not affect the plants themselves in any way, and while they are not suitable for big infestations, they can help control and prevent smaller-scale problems. The best bugs to introduce for spider mite control are:

  • Ladybugs
  • Lacewings
  • Minute pirate bugs
  • Predatory mites
  • Six spotted thrips
  • Western flower thrips

Organic Pesticides and Essential Oils

There is now a wide range of organic pesticides available on the market, with many of them doing a great job of controlling and preventing spider mite infestations. Products like Spinosad, Essentria IC3, SM-90, and NukeEm are all pretty budget-friendly and will do a great job with spider mite prevention. We have already briefly touched on neem oil, but let's have a bit more of an in-depth look at this fantastic product. Neem oil is, without a shadow of a doubt, the most popular organic spider mite prevention option currently available. Why is it so popular?

There are a few key reasons. It is very safe and extremely effective at controlling not just spider mites, but also most other bugs and fungus types that are known to attack cannabis crops while almost magically leaving those beneficial insects that we love totally unaffected. To make a Neem oil foliar spray simply mix together 500ml of water, a tablespoon of neem oil, and a couple of drops of insecticidal soap. The soap (or silica) helps emulsify the oil and water, while also boosting the insecticidal qualities of the spray. This can be used regularly, even before you start to suspect that there may be a spider mite issue with your crop. Give every plant a good spray, top to bottom, and remember to spray the underside of all the leaves.

Do not use this spray in the last 2 weeks or so of flower, and always protect any budding sites from the spray as neem oil and smokable cannabis are the best of friends. There is no health risk as such, but the oil mixture can have an adverse effect on the quality and yield of the harvest if applied to the bedding sites. If you have no access to neem oil, there is a range of other essential oils that can take its place. These include: 

  • Lemon oil
  • Peppermint oil
  • Rosemary oil
  • Eucalyptus oil
  • Cinnamon oil
  • Lavender oil
  • Tea Tree oil

While these oils may not be as effective as neem, they can be used in the same way and will have some insecticidal and fungicidal benefits.

8. In Conclusion

Spider mites are the worst bugs that can attack your plant. Even though they don’t feed on the roots or something more serious like Fungus gnats, they can lay eggs inside the buds, being able to compromise the entire main cola. Their webbing can also get stuck to the trichomes on the buds and it will be impossible to remove them completely, affecting yields and quality. As with all other pests, we recommend checking your plants every day and take action as soon as you see any sign of bugs.

22 April 2022