How To Spot, Prevent, And Treat Spider Mites On Cannabis

How To Spot, Prevent, And Treat Spider Mites On Cannabis

Spider mites are the most common and most deadly of pests you’re going to encounter when growing cannabis. Their huge reproductive capacity makes them a dangerous treat and, if left untreated, they can destroy your crops in a couple of weeks time. In this article we cover what they are, hot to spot and treat them and how to prevent them from infesting your grow.

Spider mites are members of the Acari family – Tetranychidae which includes about 1200 species. Although many think of them as insects, they are actually arachnids and have 8 legs. Although they’re closely related to spiders they got their name because of the webs they make, not because they’re in the same family.

They are simple creatures, composed from the head and from the body, usually about 1mm in size. As they hatch, their bodies will go from transparent with 2 black spots on the back, from which they get their name – “two spotted spider mites”, to red, orange, yellow, green or brown in color. The color of the adults often depends on the crop on which they occur.

They are the most common pests you’d get on a cannabis grow but they can infect other plants, fruit and vegetables too. The biggest issue with spider mites is their great reproductive capacity, it takes just 3 days to reproduce and 5 days for the egg to become fully mature. They can reproduce sexually as well as asexually and one mite can lay anywhere from 20 to 200 eggs a day. They usually live from 3 days up to 3 weeks if given the perfect environment. If left untreated they can be quite deadly, seriously stunting and slowing down or even killing the entire grow.

Usually, when you see them – it means that there’s an infestation going on. Majority of the mite population resides on the bottom side of the leaf, feeding on plant tissue and plant sap by puncturing the cells and sucking out their content while leaving white or yellow spots behind. If not treated, the leaf will turn yellow and fall off and the infestation will spread like wildfire. With a lot of infected leaves, PH and rot issues are possible too, so you should remove all the leaves that are too much damaged – let’s say if half or more of the leaf is affected, you should remove it.

Telltale signs would be tiny white specs, or byte marks on the leaves, and leaves getting sucked dry or hurling up. Also, any discoloration, deformation, wilting, distortion, spotting or streaking of the leaves may too be a sign of a spider mite infestation. If left untreated and allowed to progress, nymph and adult spider mites would also make silky, thin, protective webs all over your grow room, whose purpose is to shield them from predators.

Outdoors, it’s mostly shaded and protected spots, where there’s no significant air movement, where mites will find their home, especially if there have been periods of no rain for longer periods of time. Usually, they’ll eat their way from bottom to top, so bottom growth, that’s a bit shielded is where you should look for them first.

When it comes to controlling and treating the mites infestation, it’s advisable to attack them by using multiple different approaches. Known to develop the tolerance and resistance to even harmful chemical pesticides, it’s important to combine efforts and try more than one approach.

Mites don’t like cold weather, so lowering your temps to below 20C will help them feel unwanted. By adding good and constant airflow, you will get your plant stalks and branches to get stronger and you’ll make an unpleasant environment for all pests and insects living there. Spider mites don’t like humid and wet environments too, so if possible, increase the RH but keep an eye for mold or rot, especially during flowering.

By adjusting the environmental factors, we’ve built a hostile environment for mites but to get them into control we need to stop them reproducing and start killing them. And to do both, we can use either predatory insects or we can use various chemical solutions. As we think that harmful chemicals, such as pesticides and herbicides, shouldn’t be used for something that’s meant for human consumption, especially medicine – chemical solutions suggested are totally bio and eco friendly.

Spraying your plants, especially when they are in later stages of flowering, with anything is not a welcomed option by any grower. It can alter and effect the taste and overall quality of your crop. To treat the infestation in a more natural way, growers use predatory insects.

General predators like ladybugs or green lacewings will go after all kinds of pests – whiteflies, fungus gnats as well as mites. Bigeyed or Minute pirate bugs or Western flower or Six Spotted thrips will attack spider mites specifically, especially concentrating themselves on the eggs but they will attack larva and mature mites as well.

Predatory insects are great to finish the job, and once you’ve applied your water solutions and washed your plants with it, insects will go after the eggs and the parts that are hardly visible to the naked eye.

All solutions work in 2 ways – one is to smother and suffocate them and the other is to essentially poison them from the inside. Soaps or selective detergents dissolve the cuticle – the wax layer of the mites body by eating it from inside. Because of the alcohol in them, detergents tend to dissolve the wax layer better but they are more phytotoxic, which may end up burning or damaging the plant. Vegetable oil, such as soybean, canola or cottonseed tends to smother the mites, leaving a sticky, thick residue on the plant. Paraffinic or narrow range oils – chemically react to the wax layer and destroy it, eating the mite from inside.

The ‘problem’ with using any solutions that eat up the waxy cuticle is that cannabis leaves have a very similar wax layer of their own – that helps to keep the water and the humidity inside them. Levels and concentrations that are used to kill the mites are significantly lower than the ones needed to damage the leaves but they can accumulate and, if left untreated, end up hurting your plant or at least damaging the quality of your harvest.

Although there are many good and reliable products that you can buy in any growshop, it’s quite easy to make your own too. Mighty Wash or Mighty, Azamax, different insecticidal soaps and detergents are generally as effective as your own mixture, especially when used in combination.

Neem oil and products refined and distilled from it work both as insect growth regulators – causing the mites to become less reproductive and less hungry, as well as smothering them. Mix a teaspoon of neem oil with a gallon of water and a few drops of dish soap or plant detergent but keep in mind that neem oil is photosensitive so spraying your plants with neem should only be done in or around the dark cycle or night.

You can use peppermint, eucalyptus, lemon, cinnamon or rosemary oil too and in order not to damage your plants as well as mites, concentrations of oil shouldn’t be greater than 1-2%. Some of those oils have very intense aromas and they can end up changing your plants natural smells and flavors, especially if used later in flower.

It’s important to notice that Neem can take up to 2 months to fully leave your plant system and some people have reported to have medical issues, that some contribute to use of certain neem oil products.

Alcohol based solution – whether it’s ethanol or isopropyl, mix it with water and dish soap – about 15% alcohol and a few drops of soap and apply the same way as oil based solution.

Whatever solution you end up mixing and using, applying it is always the same. Mix all ingredients with lukewarm water, it dissolves and disperse better and makes for an even application. Depending on your area, you may want to use anything from a spray bottle to a large sprayer but generally the smaller the mist it generates the better. By adding soap or detergent to the mix, you’re making sure that your solution sticks to the leaves and infected areas, as well as that it dissolves the wax parts of the mites’ bodies.

Shower your plants with your solution, make sure you wash the bottom of the leaves too, because that’s where the majority of them will be. It’s advisable to shower your plants some 15-20 minutes before the dark cycle, in order not to cause any burn issues, water drops might cause. After you’ve showered your plants, clean the grow environment with 1tbsp of bleach per gallon of water or with a solution of 1/10 of rubbing alcohol – isopropyl or ethanol and water.

It’s important to repeat the procedure, at least 3-4 times, spraying your plants every 3 days. That way the eggs that will hatch will get attacked when they are most vulnerable and prevent them from further reproducing. Before spraying your plants again, you can wash them down with water, to remove the dead mites.


Having a clean environment is more than half of prevention. Make sure you pick up any dead plant material, soil medium or debris that might be left when tending your plants, as well as make sure there’s no stale or spilled water anywhere.

If you’re growing indoors, all infestation will come from contaminated sources that came from outdoors. Mites are very common and they can be found in most vegetable gardens and they are super easy to transport. Pets, as well as humans, can bring eggs, larva and mature mites if they aren’t careful. Cleaning your clothes, or changing them, after you’ve been exposed to other gardens, before you enter the grow room is highly advisable.

It’s important to seal all your air holes, to have a tight and closed environment and to use a filter for your intake, especially if you’re using the outdoor air, usually for cooling down.

Steady airflow, below and on top of your plants will also make it harder for any pests to find home there. Wash down with bleach and rubbing alcohol any new equipment, especially if it’s been used before in other gardens, before you introduce it to yours.

If you’re adding a new plant to your garden, it’s smart to put them in quarantine for 10-15 days, in order to make sure that there aren’t any eggs or pests that may have come with it that could potentially infect your whole crop.

As with any problem, it’s always better to prevent it from happening than to deal with the aftermath and the consequences once it does happen. Having a clean environment, cleaning yourself, any new equipment, plants or anything else you’re introducing to the garden is highly advisable.

If you happen to get infested, use more than one solution and apply it as long as you see mites.If you’re into flowering, you might want to consider using predatory insects, as they provide a cleaner and safer alternative and don’t alter your harvest quality. If you happen to use chemical solutions, be mindful of their application and aftereffect.

Remember: It is illegal to germinate cannabis seeds in many countries including the UK. It is our duty to inform you of this fact and to urge you to obey all of your local laws to the letter. The Vault only ever sells or sends out seeds for souvenir, collection or novelty purposes.

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