marijuana pests spider grow

Most common marijuana plant pests: spider mite

  • The spider mite (Tetranychus urticae) is one of the most common pests for marijuana plants and also one of the most feared.
  • These tiny fellow travellers, very common in indoor crops, are very capable of ruining your marijuana harvest if they are not stopped in time.
  • Below we will explain everything you need to know about this inconvenient arachnid because, if you are starting out in the noble art of growing your own marijuana, be sure that you will be visited by this pest sooner or later. The key to preventing them from spoiling your plants is identifying them in time and acting quickly, so let's get on with it.
marijuana pests spider grow

How to identify spider mites

At first glance you might find it hard to see this tiny spider, they are actually quite small and stay on the underside of the leaves, meaning that they are hard to detect visually. A very clear sign indicating the presence of these microscopic mites on your cannabis plants is the appearance of small yellow or translucent patches on the leaves; this is the trail they leave after feeding, as the spider mite sucks out the marijuana plant's vital fluids and this translates into very characteristic and easily recognisable yellowish specks on top of the leaves.

If you see this type of "yellow dots" on your marijuana plants, you can fully confirm that the cause are spider mites by wetting the underside of the leaf with water, if the infection is quite advanced, in this way you can see the tiny spiderwebs on stalks and leaves. You can also use a magnifying glass, a weak one is enough to see this mite without difficulty. The red spider mite can be whitish-yellow in colour or with two brown patches, and its eggs are transparent.

Damage caused by spider mites on cannabis plants

This type of mite feeds off the plant's vital sap, it is a plague that mostly affects cultivations with high temperatures (the higher the temperature the faster they reproduce), and through their suction they debilitate the general vigour of the plant and obstruct its metabolic functions. When they extract the sap from the leaves, these cannot carry out their function (they cannot produce chlorophyll, therefore photosynthesis is not carried out correctly), and depending on how large the infestation is, the damage will be partial or total. If the infestation is advanced, leaves will turn yellow and fall off the plant.

This plague grows and expands very quickly, and if measures are not taken quickly, it can even kill the plant. The spider mite is very common in indoor crops and, although it also attacks outdoor cannabis crops, It becomes more lethal indoors as there are no predators that are normally found in natural ecosystems. In crops with very advanced infestations, the spiderwebs can even cover the whole plant.

How do we prevent the appearance of spider mites?

Like with any other plague or infection that can attack your marijuana crop, the best way to fight spider mites is preventing their appearance. These are the measures you can take to avoid this pest:

  • Cleanliness: keep the cultivation area clean and tidy. Disinfect all the tools you use in your grow room every day and change clothes when you enter it to avoid bringing in any pests from outside.
  • Wash the cuttings or plants in a vegetative state: spray them once with Neem oil preventively.
  • Control the humidity: the spider mite develops in dry environments and with a temperature of 21-27 °C and reproduces very quickly if the temperature exceeds 27 degrees. Therefore, maintain an adequate temperature that does not exceed 25 degrees and a relative humidity of 55-60%.
  • Introduce predator mites: as a preventive measure you can use Neoseiulus (Amblyseius) californicus, a micro-mite that eats other mites such as the spider mite and that is harmless for the plants. Applied and bred correctly, these mites work very well, as they feed off other mites and do not attack vegetable matter. If you use this method, you must bear in mind that these predators can only eat a certain number of mites per day (20 eggs or 5 adults), therefore, if there is an infection and it is very advanced, they will be unable to stop it by themselves. You must distribute them among all the plants, as they find it difficult to move from plant to plant.

What do you do if your marijuana crop has spider mites?

  • Take special care to keep everything clean.
  • Remove the infected plants and try to prevent the plague from spreading.
  • Remove leaves that have more than 50% affected and throw them away and don't touch other parts of the plant or other plants during this process to avoid spreading the infection.
  • Create a hostile environment by reducing the temperature to 16 degrees and increase the humidity.
  • Spray the leaves with cold water, this literally removes the mites. If the infection is not too advanced, you can also remove them manually with the aid of a small sponge. Get rid of the sponge once you have finished and wash your hands and all the tools you have used carefully.
  • You can use organic remedies such as:
  1. Neem oil: this works very well.
  2. Insecticidal soap: works well in general and will take two or three applications with intervals of five to ten days.
  3. Pyrethrum oil: an excellent ally to control this pest, a good natural insecticide that we recommend you apply two or three times leaving an interval of five days in between.


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  1. 4 out of 5
    Great info on red spider mite. Thank you

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