How to eliminate the red spider mites in marijuana plants?

How to eliminate the red spider mites in marijuana plants?

What are Red Spider Mites?

Red spider mites (Tetranychus Urticae) are a type of small 0.5mm mite from the Tetranychidae family, also known as Spider Mites, capable of spinning webs which is why they’re often confused with spiders. They can be brown and deep red depending on the stage they’re in. They tend to hide on the underside of the leaves and in their webs, allowing them to trap natural predators and protect themselves from certain types of acaricides.

Over the past few years, spider mites have been occurring more often in cannabis grows; they used to die off when winter rolled around outdoors. However, they can now stick around all year round indoors and in greenhouses, and combined with the increasing temperatures of our planet they can last for all year round anywhere they want, getting stronger each and every year.

Spider Mites and Cannabis Plants

Spider mites don’t produce large markings on your plants unlike other infestations such as caterpillars, slugs or snails. However, spider mites can bite your plants leaves hundreds of times until they’re absolutely covered in small grey dots; they absorb sap and empty out your leaves. When this infestation is in its most advanced stage it can cover buds with its webbing which can cause you to lose quite a lot of harvest.

Preventing and getting rid of spider mites ASAP is absolutely necessary, especially if you’ve seen any signs; it can develop and thrive in no time at all if found in the right conditions, colonizing entire plants within days.

Red spider mite under a La Huerta Grow Shop microscope
Red spider mite under a La Huerta Grow Shop microscope

How to Identify Red Spider Mites

  • Even though these mites are super small, they’re easy to identify due to their greenish brown color or intense red color and their slow movement along the plant. Sometimes, in outdoor grows, another similar mite may appear but it won’t damage your plants; you can tell them apart because they move much faster than red spider mites and they don’t leave any markings on your plant.
  • Red spider mites can be found on both sides of the leaves; the upper part is where they feed from and they lay their eggs along the bottom, just like white flies.
  • Red spider mites leave small white or grey dots along the leaves of your plants as they feed.
  • If you run your finger over the leaf where you think there might be spider mites and it goes a sort of red color, it’s most likely red spider mites.
  • In advanced infestations it can also spin webs on the leaves, stems and flowers.
  • The best way to identify this inset infestation is by using a x100 microscope or magnifying glass on the underside of the leaves. Spider mites in their larvae state have three pairs of legs, and in their adult state they have 4 pairs; they’re easily identifiable.
Cannabis leaf infested with red spider mites
Cannabis leaf infested with red spider mites

Red Spider Mite Infestation Characteristics

  • Red Spider Mites are extremely common in outdoor growsindoor grows and greenhouse grows. They do well in warm climates, which is why they start to shop up during spring/summer.
  • Red spider mites are incredibly sturdy and can live out winter in other plants, leaves and vegetation. Clean all of your flowerpots and growing material before and after growing in order to avoid infestations going from one grow to another. Don’t reuse substrates, especially if you’ve had insect infestations previously.
  • In the middle of summer they can complete their life cycle in just over a week; they can easily spread rapidly and can become quite a problem. Plus, this coincides with your plants’ flowering period so you’ll need to take preventive measures in order to make sure you can successfully harvest healthy cannabis plants.
  • Every female red spider mite can lay between 3 and 5 eggs a day, which makes it easy for an infestation to suddenly appear. When they can no longer feed off of the plant, they group up on the edges of the leaves in order to move around with the wind to other leaves and plants.
  • In grows with little ventilation, insufficient watering and/or humidity, or grows where heat can accumulate like glassed greenhouses, red spider mites can really flourish and breed quite heavily if the conditions are met.

Red Spider Mite Life Cycle

Red spider mites goes through the following stages: egg (2 – 7 days), larva (2 – 3 days), proto and deutonymph (5 – 7 days) and adult (10 – 30 days).

  • In indoor grows they can appear at almost any time, especially if you bring new plants in and they’re infected.
  • In outdoor grows they tend to appear in spring/summer, once it begins to heat up. They reproduce easily in temperatures over 15 – 20°C.
  • They prefer areas that are warm, dry and poorly ventilated.
Cannabis plant during flowering under attack by red spider mites.
Cannabis plant during flowering under attack by red spider mites.

Red Spider Mite Phases

  • Egg: the eggs that red spider mites lay tend to be on the underside of the leaves, in small groups. One red spider mite can lay up to 100 eggs over their entire life cycle. Eggs take about 2 – 7 days to hatch depending on the environmental conditions in which they’re in.
  • Larva: this is the most fragile period spider mites go through, as they aren’t fully developed yet. This is the perfect time to get rid of spider mites, as they’re easier to get rid of, although it can be difficult to catch them in this stage. It’s much easier to spot them when they’re adults or are in various different stages on your plant. During this stage, red spider mites have six legs. The larva stage lasts just 2 – 3 days.
  • Proto and deutonymph: during the protonymph and deutonymph stages this insect grows an additional two legs. This process takes about 7 days.
  • Adult: these are the most dangerous for your cannabis plants; females can lay around 5 eggs a day and up to 100 during their entire life cycle, making them the main causes of the infestation. Adults can live for 10 – 30 days depending on the conditions and how strong they are.

Spider Mite Damage

  • Leaf damage: they can bite your plants’ leaves in hundreds of places, which can easily be seen as small white dots all over your plant. This causes permanent leaf discoloration.
  • Plant stress: your plants are under a lot of stress and can end up losing leaves and slowing their growth or flowering depending on how advanced the insect infestation is.
  • Less quantity and quality: your plants will produce less yield of lower quality; buds end up smaller and may end up covered in spider webs.
  • Bad-tasting buds: your flowers may end up damaged beyond repair with illness due to the bites and insect excrement, which can make for a nasty flavour.
Flowering cannabis plant at the start of a red spider mite infestation.
Flowering cannabis plant at the start of a red spider mite infestation.

How to Prevent Red Spider Mites in Cannabis

As with all infestations, we recommend preventing it rather than getting rid of it when it’s too late. There are all types of tips and tricks when it comes to getting rid of red spider mites:

  • Avoid excess nitrogen when fertilizing; this attracts spider mites and other infestations.
  • When growing outdoors, keep your cannabis plants far away from other plants; many types of spider can stick around during the winter in other plants.
  • When growing indoors make sure the room is properly ventilated to avoid excess heat which can make it easier for an infestation to appear. If you want to know more about ventilation and air extraction, check out our post about ventilation for indoor cannabis grows.
  • High humidity isn’t good for this insect, which is why they tend to go to week or dried out plants.
  • Make sure to be as hygienic as possible; change your clothes before entering your grow room.
  • Check your plants periodically to check if they have adult red spider mites, eggs, etc. Check the undersides of the leaves and keep in mind that they tend to bunch together.
  • If you’re using homemade compost or you’re adding manure to your plants, make sure that they have been properly fermented and do not contain insects.
  • If you’re just finishing up your grow and have had red spider mites, you’re going to want to make sure that they haven’t stuck around. You can use Solfac Automatic Forte to get rid of any stragglers (toxic product, read instructions well).
Flowering cannabis plant infected with red spider mites
Flowering cannabis plant infected with red spider mites.

Getting Rid of Red Spider Mites During Growth

Once you see signs of infestation in your plants, all you have left to do is to fight it off as best you can in order to get rid of it as soon as possible. During the growth stage there are more ways to efficiently get rid of this infestation as your plants are smaller and you can spray them without damaging buds. You can use bio and chemical acaricides.

Bio insecticides for growth

  • If the infestation is present during the growth period, we recommend using insecticidal soap such as Mobet alongside organic pyrethrins such as Spruzit, which contains rapeseed oil which asphyxiates red spider mite eggs.
  • You can also use bio acaricides designed specifically for red spider mites such as Plant Vitality by BAC.
  • Another great option when it comes to getting rid of red spider mites is to treat your plants suing natural Elosal sulphur which also works against fungi such as oidium (mildew).
Cannabis plant under siege by red spider mites in the growth period
Cannabis plant under siege by red spider mites in the growth period.

Chemical Insecticides for Growth

If you have an indoor grow and you’ve had a recent insect infestation, you can guarantee to be rid of it by using Solfac Automatic Forte, which automatically sprays the room. Make sure to carefully read the instructions.

Getting Rid of Red Spider Mites During Flowering

During the flowering stage in cannabis plants you can only use bio acaricides; chemicals stick around for much too long in the plant and it could be dangerous to use them at this stage. You can also use natural predators to get rid of the infestations both indoors and outdoors.

Bio Insecticides for Flowering

  • During the flowering period is the worst possible moment for this infestation to appear, so you’ll need to act fast and treat your plants correctly in order to avoid adding issues.
  • To fight off red spider mites you can use bio acaricides such as Spruzit which can kill eggs. You can also use it alongside insecticidal soap such as Mobet.
  • Another highly efficient acaricide is Plant Vitality.
  • Make sure to check on your plants daily, especially the underside of the leaves. In order to manually get rid of adults, larvae, protonymphs and eggs, you can use a solution of water and the three previously mentioned products in the manufacturer’s recommended proportions; in order to do this you’ll need to use a sponge or soaked cotton on the underside of the leaves.
Cannabis plant under siege during the flowering period
Cannabis plant under siege during the flowering period.

General Advice

Keep in mind that red spider mites have numerous natural enemies. Some of the easiest to find are phytocide mites known as Phytoseiulus Persimilis, Noeseiulus Californicus and Amblyseius Californicus; you can also use Feltiella Acarisuga, a type of fly larva. Check with our team of experts if you’re looking to get natural predators to fight any type of insect infestation.


  • Red spider mites tend to colonize one plant and move on to another when they feel threatened. If you find an infested plant, move it away from the rest of your plants and treat them all using acaricide.
  • If you suspect that you have an infestation you should inspect your plants daily and get rid of any eggs and adults, by hand if necessary.
  • Make sure to keep your grow room clean and the environmental conditions stable (especially ventilation).
  • We recommend reading and following your insecticide instructions carefully, using the recommended safety measures for each one. If you have any questions check with our team of professionals.
  • At La Huerta Grow Shop we always recommend growing cannabis plants organically and naturally, respecting the environment. When possible, use organic insecticides and preventive products. source

How to eliminate the red spider mites in marijuana plants?

What is a red spider mite?

The red spider mite (tetranychus urticae) is a type of mite that usually infects cannabis crops while feeding on the leaves. This pest breeds quickly and they eventually build cobwebs around the flowers, so you’ll want to avoid them at all costs. Its ability to develop resistance to pest controls worries any grower. They generally live on the underside of plant leaves, where they can form silk cloth.

They are less than 1 millimeter in size and can be red or black. They prefer warm and dry conditions and lay transparent eggs that can hatch in just 3 days. The offspring are sexually active 5 days after birth, and can live up to 2-4 weeks, laying up to 20 eggs per day.

How to fight the red spider mite?

Observation is key to spotting the red spider. Some people can see them moving down the back of the leaves, while others need help of a magnifying glass to spot them. Either way, be sure to regularly inspect the plants, and if you’re looking at cobwebs, you’re certainly dealing with an infestation of this insect. The appearance of a few bugs does not mean that there is necessarily a plague. If some red spiders mites are found under the leaves, they can be plucked and thrown into a bag away from the crop, but keep watching and check that they do not multiply.

Prevention is key and high humidity will slow down the reproduction rate of this pest, so spray plant foliage frequently with water. There are also home remedies; some growers water the plants with a mixture of water and alcohol (9: 1) as it kills the mites without hurting the plants.

If your plant has already started the flowering stage, it is best to use natural products so as not to hurt the plant. The use of potassium soap is a good solution to control this pest. This product is a combination of vegetable fats mixed with an alkali (product with a very high pH) and two or three applications should be applied at intervals of five to ten days, until the hardest day.

On the other hand, biological control is one of the best methods to fight the red spider mite. You’ll need natural predators that must be introduced into the crop. They are totally harmless to the plants and feed on the red spider mite.

The best known are: Phytoseiulus persimilis, Noeseiulus Californicus and Amblyseius swirski.

Specific chemical insecticides for this type of pest also work, but they should be used with precaution and only if the plant is already infested, as they are not preventive. These products are known commercially under the name of acaricides or miticides. Ideally, apply them before the flowering stage, at which point it will be much more difficult to combat the pest.

Lastly, you will want to clean your grow room, grow tent, or greenhouse if you had this type of pest. There are many ways to clean and disinfect using products like hydrogen peroxide or alcohols. Be thorough, be clean, and be patient. source


How to Get Rid of Spider Mites on Cannabis Plants

Spider mites are considered as a common cannabis pest. It can be very problematic to protect cannabis plants and get rid of spider mites due to their powerful capabilities.  They are named as spider mites due to their property of creating a web around cannabis leaves and flowers.

Reasons why spider mites are harmful to cannabis plants

Here are a few reasons why spider mites cause problems for cannabis growers and damage cannabis plants.

  • The reproduction of spider mites is very fast. A million mites can reproduce in a very short time period i.e. less than a month.
  • Spider mites are so tiny that they are hard to notice and they possess a special ability that they can become immune to killing methods and killer sprays.
  • Spider mites feed on chlorophyll. They disrupt the process of photosynthesis by destroying chlorophyll and it can cause starvation; and  eventually death of cannabis plants.
  • They can result in a big infestation in a short time period. Due to webbing and high resistance just like zombies, spider mites can ruin the entire cannabis crop if effective preventive measures are not taken in time.

Eradication methods to get rid of spider mites 

A long-term approach is required if you want to eradicate spider mites completely from your cannabis crop. There exists multiple ways to prevent their infestation which are listed as follows:

  • Using organic compost mulch/lady bugs

Organic compost mulch involves predatory mites that eat spider mites. Ladybugs are also well-known for being natural predators of spider mites in this regard, they can kill spider mites and are beneficial for cannabis plants.

  • Using hard water spray

Use a water spray on cannabis plants multiple times in a row following a routine (i.e. 3 mornings consistently). Due to water pressure, spider mites fall to the ground and are unable to move. Lack of food can eventually cause their death.

  • Using vacuum cleaner

A handheld vacuum cleaner can suck the spider mites straight off of cannabis leaves. It is a bit time consuming process but it can remove spider mites in an effective way. The benefit of this method is that all the lifecycle stages of the spider mites will get targeted by the vacuum cleaner.

  • Using home-made killing solutions

A mixture of home-made solutions such as mixing a spoon of bleach in a bottle of water or mixing alcohol in water, can help in getting rid of spider mites on cannabis plants.


Analyze the growth of your cannabis plants thoroughly and if you feel symptoms of spider mites then opt the best available method. As explained above, spider mites actively reappear on cannabis plants even after application of various eradication methods. Therefore, it is necessary to keep employing preventive strategies on regular basis without any negligence.  In case, if you use commercial sprays then read the instructions carefully and apply them with great care. source

Leave a Reply