Spider Mites in Marijuana Grow Room, How-to Identify, Prevent, Kill

Spider mites on Cannabis Plants

How to identify and deal with an infestation

Hey there and welcome (back) to Free the Tree!
Today we decided to cover a nasty problem… Spider Mites, related to spiders, ticks, and other mites, and they can do heavy damage to a cannabis crop .
This little guys are one of the most common cannabis pests, giving a hard time to indoor and outdoor growers all over the world since they can be very difficult to get rid of.

This is actually something that we’ve been dealing with for awhile now, so we’re not promising a silver bullet solution, as these suckers are fighters.

Alright, enough said, let’s get into it

Dealing with Spidemites – Table of Content

I. Spider Mites – Learning about the foe

  • Characteristics of Spider Mites
  • The Lifecycle of Spider Mites
  • Spider mites spreading step by step
  • The Environment and spider mite colonies
    – What environment do Spider Mites hate(must read)
    – Thriving environment for Spider Mites
  • Spider mites in the U.S.A
  • How did you get spider mites?

II. How to get rid of Spider Mites in a Cannabis Culture

III. FAQ around Spider Mites and Marijuana

  • What is the base leaf
  • How to avoid colony spreading
  • Do Spider Mites bites humans?
  • Can I get Spider Mites from clones? (coming soon)
  • Do Spider Mites come from outside? (coming soon)
  • Can I get Spider Mites from people? (coming soon)

IV. Spider Mites Myth Busting

  • Truth or Myth –Spider Mites can reappear months later.
  • True or False – In less than a month you can have a colony of over 1 Million individuals (coming soon)
  • Spider Mites explode in very humid conditions (coming soon)

I. Knowing more about the Tetranychidae Family (aka Spider Mites)

Characteristics of spider mites

As we said we personally had to deal with this issue, and spent sooooo much time searching on the internet for information. From Grow Journals to blogs, passing by sites selling products and our local grow shop, we searched everywhere for info, heard everything and it’s opposite.

After that struggle, we decided to regroup everything in one spot, here’s a list of the different characteristics, hope it helps out!

Spider mites Characteristics
Family Spider mites are part of the Tetranychidae family of Acari’s which includes over 1 200 different species.

The most common types are the

Environment Thrives in hot and dry environments
Size of adult An adult spider mite is under 1mm long, making it almost invisible to an untrained human eye.
Lifespand Spider mites can live up to 2/3 weeks.
Hatching and
sexual maturity
Under optimal conditions (27°C/80°F):

  • The eggs will hatch in about 3 days.
  • The newly born will become sexually mature in as little as 5 days.

On average 75% of newborns will be female.

reproducing cycle Spider mites become sexually mature in 3 to 5 days, after which they can lay up to 20 eggs a day.
If the full life of a spider mite it will lay hundreds of eggs.
Visible Colour Depending on the type of mites they will be either:

  • White
  • Red
  • Black
  • White with 2 black spots (aka the 2 spotted mite, fierce for marijuana cultures)
Fertility of females Once a male has fertilised a female she is fertile for life. Meaning that every day she can lay 20 more eggs without needing a male around.
This is another reason why these little guys are so vicious
Birth of Males and Females When mated, females avoid the fecundation of some eggs in order to produce males.
Only fertilized eggs will produce females.
Un-mated and unfertilized females still lay eggs that originate exclusively haploid males.
Generally Spider mites will keep a nice balance of 75% Females and 25% in order to fully infest a plantation very quickly.
What do they feed on Spider mites feed on the leaves by removing the chlorophyll (green pigment) with their stylet like mouth.
This is why you see these white marks on the leaves, those area’s are deprived of chlorophyll, thus their green color.

Keep in mind that a leaf without chlorophyll cannot participate in photosynthesis.

Level of danger
for plants
HIGH – This suckers will invade your place, at first slowly, but the more mites you have the quicker they invade.
This is especially dangerous since the invasion in generally discovered when it’s too late.
Don’t wait until they’ve conquered multiple plants, as soon as you spot that base leaf(s) get rid of it/them! (below for more on that)
Plant invasion capacity Spider mites invade by colonising and feeding on leafs. Being so small a single mite doesn’t cover much ground, a colony on the other hand…
Once the leaf is covered, some of the female mites of that colony will migrate to a new leaf in order to feed on it.This happens much faster that you might expect, within the first rounds new-borns some of those little guys will go search for their own leaf.Generally they will stick to the same plant except if:

  • Leafs are close and/or touch which is generally the case in a grow room. This makes it easy for a mite to pass on to a new plant.
  • You main leafs already have a couple mites on them, the one’s searching for new ground prefer to start off on an un-colonised leaf.
  • Your plant it totally colonised. At this point they have no other choice but to invade another plant.
    Generally they will have already spread to other plant via leaf proximity before this happens
Speed of spreading For this let’s take back the numbers we gave you further up.
1 female mite can lay up to 20 eggs a day. In 8 days the 20 eggs have hatched, 75% of those are females and are ready to lay eggs. So:

  • 8 days after having 1 mite you will have 16 females mites, each day laying 20 more eggs.
  • 3 days later try to guess how many you’ll have…. yep that’s it!
    61 total females, and over 3100 eggs
  • If untreated, by day 21 you’ll have more than 6500 females and almost 400 000 eggs.
  • And by day 30.. that number of mature females would be up to over 840 000 with over 40 million eggs and non-mature spider mites.

If you remember right, the lifespand is of 2/3weeks. At the latest, when your first spider mite naturally dies, she will have given birth to a colony of over 6000 individuals, scary!

As you can see the spreading is exponential, this is why you must identify and treat them quickly and swiftly, it’s no joke. The survival of your babies is at stake.

How do they spread Coming soon
Genera Spider mites include over 1 200 species. The most common for marijuana growers are the
If you want to know more on the different species of this type of mite, check out the Wikipedia page dedicated to them.
Resistance to treatment High – Spider mites are known to develop resistance very quickly. For example some individuals that aren’t killed or the eggs can become immune to whatever you used.

It is important to have 2 different counter-measures, whether they’re organic or pesticides so that in case one individual has become immune you kill it in the second round.

Predatory mites The best predator are actually lady bud larvae’s; they will feed on the spider mites and their eggs and will not harm your plant. Introducing these insects within your ecosystem is a great counter-measure for spidermite infestations, especially for outdoor growers.

The lifecycle of Spider Mites

In optimal conditions, from egg to death the lifespan of Spider Mites is a little over 3 weeks, in the best cases. In that period in time just one of those small little spiders can devastate a harvest.

Here’s the different stages of life and their average length.

Stage of life LENGTH IN TIME
Hatching period As short as 3 days in a hot (27°C/80°F) and dry environment
Sexual Maturity Spider Mites will reach sexual maturity in as little as 5 days. It can take longer if the environment is cold or humid.
Mating period Female Tetranychidae are active from 2 to 4 weeks, laying up to 20 eggs a day. This gives them time to reach hundreds of eggs within their life.

This is also the stage of their life where they create the webbing on your plant in order to safely lay their eggs.

If you start seeing the webbing with a naked eye and without using water to spray under the leafs you’ve got a serious infestation on your hands

Post-mating period As most animals (basically all except humans), once the female is no longer able to lay eggs she will die.

Spider mite eggs – Photo credit to Epic Gardening


Ministry of Agriculture, Food and Rural Affairs

Mite Pests in Greenhouse Crops: Description, Biology and Management

Agdex#: 290/621
Publication Date: May 2014
Order#: 14-013
Last Reviewed:
Written by: Graeme Murphy — Greenhouse Floriculture IPM Specialist/OMAFRA; Gillian Ferguson — Greenhouse Vegetable IPM Specialist/OMAFRA; Les Shipp — Research Scientist/Agriculture and Agri-Food Canada

Table of Contents


Mites are more closely related to spiders than they are to insects. They are small (usually less than 1 mm in length), eight-legged organisms, with a wide host range, capable of causing extensive damage to a range of greenhouse crops. There are several species of concern. The most important is the twospotted spider mite (Tetranychus urticae); however, other species that can also cause significant damage include two other spider mites, the Lewis mite (Eotetranychus lewisi) and the carmine spider mite (Tetranychus cinnabarinus), as well as the broad mite (Polyphagotarsonemus latus), the cyclamen mite (Tarsonemus pallidus), the tomato russet mite (Aculops lycopersici) and the bulb mite (Rhizoglyphus spp).

Description and Life History

Mites pass through a few stages from egg to adult. The eggs of the above-mentioned pests are laid singly on foliage or in the growing points of plants (or in the case of the bulb mite, in the soil).

Newly hatched mites pass through a six-legged larval stage and two eight-legged nymphal stages known respectively as the protonymph and deutonymph. The last of these is an immobile resting stage from which the adult emerges.

The twospotted spider mite (TSSM) (Figure 1) has a host range of hundreds of plant species, including all major vegetable crops and many ornamental crops. The eight-legged female adult is approximately 0.5 mm long, with a rounded abdomen. The male is distinguished from the female by its smaller, narrower body and pointed abdomen. Adults range from pale yellow to orange to brown or black. Day-lengths of 12 hr and less, decreasing temperatures and a deteriorating food source will induce diapause (an overwintering stage similar to hibernation).

Figure 1. Twospotted spider mite adult.

The diapausing stage is reddish-orange in colour (Figure 2) and can tolerate very low temperatures. A short spell of heating is not sufficient to break diapause.

Figure 2. Overwintering twospotted spider mite.

Close examination of leaf undersurfaces will show the mites to be miniscule moving dots. There are usually two dark spots on the body of TSSM, although this can be somewhat variable. After mating, each female mite lays approximately six pearly white eggs (Figure 3) a day. Over an average lifetime, a female lays 100 or more eggs on the undersurface of foliage. The life cycle from egg to adult ranges from 23 days at 15°C to just 4 days at 32°C. Development is fastest under hot, dry conditions.

Figure 3. Adult twospotted spider mite with eggs.

The carmine spider mite and Lewis mite are closely related to TSSM. The carmine spider mite has not been positively identified in Ontario, but it is present in greenhouses in other countries. It is difficult to distinguish from TSSM in its immature stages, but the adult stage is bright red in colour and more commonly found on vegetable crops than in ornamentals. The Lewis mite is most often found on poinsettias and, in many ways, appears similar to TSSM, although it is often found with a few small spots on its back rather than the two distinctive spots of TSSM.

Broad mite (Figure 4) and cyclamen mite are microscopic in size (0.1-0.3 mm) and can be difficult to see even with a hand lens. For this reason, growers usually only know when they are present by the damage that they cause (see Damage). The life cycle (egg-to-adult) of these mites varies from less than a week under summer conditions to 10-18 days during winter, with the broad mite developing more quickly than the cyclamen mite.

Figure 4. Broad mite adult.

These two mites can be difficult to distinguish from each other in the mobile stages. The most reliable method of identification is in the egg stage. Eggs are laid on the surface of young leaves (often along the mid-vein) or in developing flower buds or new growth. The broad mite egg has a very distinctive appearance, with small bumps covering the surface (Figure 5), compared with the cyclamen mite egg, which has a smooth surface (Figure 6).

Figure 5. Broad mite egg.

Figure 6. Cyclamen mite egg.

Tomato russet mite belongs to a different family of mites known as gall mites and is even smaller than the broad mite and cyclamen mite. It is an elongated mite approximately 0.2 mm long and 0.05 mm wide (Figure 7). It differs from other mites in having only two pairs of legs in all stages. Because of its size, it often develops large populations before being noticed. It is primarily a pest of tomato but can also occasionally be found on other members of the tomato family.

Figure 7. Tomato russet mite.

Bulb mite (Figure 8), as the name suggests, can be a pest of crops such as lilies, tulips, gladiolus, daffodils and amaryllis. Slow moving, bulb mite has a white body, 0.5-1.0 mm in length, and short reddish-brown legs.

Figure 8. Bulb mite.


Mites feed by piercing the epidermis of the plant with sucking mouthparts and removing the cell contents. The various mite pests attack different crops and can be found on different parts of the plant.

Twospotted spider mite, Lewis mite and carmine spider mite are found primarily on the underside of leaves. The feeding injury caused by TSSM and Lewis mite is very similar and starts as a yellow «stippling» where the cell contents of the leaf have been removed (Figures 9 and 10). As mite numbers increase, the entire leaf appears stippled or light-coloured on the upper surface and develops a bronzed appearance under heavy mite populations. Very heavily infested leaves become yellow and brittle, and in some cases (e.g., hibiscus), plants can exhibit a toxic response to feeding, with leaves yellowing and dropping from the plant even at quite low mite population densities.

Figure 9. Twospotted spider mite damage on rose leaves.

Figure 10. Lewis mite damage on poinsettia.

If infestations proceed without control measures, plants may be killed. These mites produce webbing that is used by the mites to disperse with the aid of air currents. Large mite populations can produce large quantities of webbing (Figures 11 and 12, which can be unsightly (especially in ornamental crops). The mites also use the webbing as protection, increasing the difficulty of control with predators and with pesticides.

Figure 11. Twospotted spider mite webbing on rose.

Figure 12. Twospotted spider mite webbing on cucumber.

Carmine spider mite feeding can result in feeding damage that includes widespread leaf yellowing and leaf drop (Figure 13).

Figure 13. Carmine mite feeding on tomato.

Broad mite and cyclamen mite each feed on a wide variety of crops and exhibit similar damage symptoms. They feed in the tight, newly emerging foliage and flower buds, with the damage becoming obvious as the plant tissue develops and enlarges. Toxins injected by the mites result in distorted, thickened and twisted growth at the top of the plant and in the flowers (Figure 14). The occurrence of these symptoms is usually the first indication that growers have a problem. These mites can be distributed throughout the greenhouse as hitchhikers on workers, equipment and even on insects such as whitefly (Figure 15).

Figure 14. Left, broad mite damage on peppers. Right, broad mite damage on cyclamen.

Figure 15. Broad mites hitchhiking on Bemisia whitefly (Source: D.E. Walter).

Although there are subtle differences in the biology and damage symptoms between these two mites, they are often treated in the same way in terms of recognizing the problem and management strategies.

Tomato russet mite is another mite where the symptoms of damage are the first sign of the presence of the pest. They are found on the leaves, stem and fruit of tomatoes and, in large numbers, result in the plant tissue taking on a bronzed appearance (Figure 16). Damage symptoms include yellowing, curling and wilting of leaves, flower abortion and bronzed, cracked fruit. If uncontrolled, they will eventually kill the plant.

Figure 16. Bronzed and cracked tomato fruit infested by russet mites .

Bulb mites live and feed on plant parts below the soil surface. Feeding scars on the bulbs can turn brown and necrotic, and the wounds can create entry points for plant pathogens. The mites are attracted to and use damaged and diseased tissue to enter the bulb and feed. Often bulb mites and disease are found coexisting. Infested bulbs can show above-ground symptoms in the form of yellowing and stunting.

Management Stategies

Spider mites

Good monitoring is critical to the early detection and management of spider mites. Pay close attention to new plant material entering the greenhouse and to susceptible crops and varieties. Monitor closely in areas of the greenhouse that are warmer and drier, e.g., around heating pipes, south-facing walls and open vents/doorways. In ornamental crops, make regular crop inspections to detect early infestations before mite populations build up. In crops such as rose, inspect both upper and lower canopies. In poinsettias, Lewis mite may be introduced on cuttings. Inspect them carefully and monitor closely throughout the crop, paying attention to all varieties.

For vegetable crops, conduct a proper clean-up at the end of the crop to reduce initial infestations in the crop that follows. It would be better to reduce, if not eliminate, populations just before the overwintering or diapausing phase of the spider mites, since the diapausing mites hibernate in the ground, hollow stems, pipe fittings, cracks and crevices during the fall and winter. The mites become active again during late winter and early spring, and infestations in the new spring crop are often found where «hot spots» occurred during the previous fall. To detect infestations early, scouts should ideally check every row weekly. The red mite stages are generally pesticide resistant and are not as readily fed upon by predators. When the red diapausing mites are detected, use soap sprays on lightly infested leaves, and remove and destroy more heavily infested leaves.

Biological Control

Spider mites can be controlled biologically using the predatory mite, Phytoseiulus persimilis. Other predatory mites used against this pest include some strains that are tolerant to high temperatures or pesticides. For example, the predatory mite Amblyseius californicus is reported to better tolerate dry conditions, while Amblyseius fallacis is resistant to some pesticides. Amblyseius andersoni is another predatory mite that has a wide range of temperature tolerances. Many Ontario growers have had good success with these predators.

Phytoseiulus persimilisPhytoseiulus persimilis is about the same size as TSSM but is pear-shaped and pale salmon to bright orange (Figure 17). It also differs from TSSM in that it does not have two spots and moves more rapidly on long legs. It feeds on spider mites and does not diapause. Without spider mites, the predators die. This means new spider mite infestations require new introductions of the predator. Adult predators feed on about seven adults or 15-20 eggs per day. At 20°C, P. persimilis reproduces at almost twice the rate of TSSM. Control with P. persimilis is best between 20°C and 26°C. At temperatures above 30°C and humidity under 60%, the predators do not thrive and seek cooler, more protected areas lower in the crop canopy. In contrast, TSSM thrive under these conditions. The predators are available commercially either mixed with vermiculite, sawdust/wood chips or on bean leaves. With either carrier, treat infested plants at the first sign of damage. Try to place a few predators onto every infested leaf. Such placement is particularly important in crops (e.g., tomato) with sticky hairs that interfere with the mobility of the predator between leaves. Before releasing the predators, ensure that they are alive and active.

Figure 17. Phytoseiulus persimilis.

Amblyseius californicusAmblyseius californicus is a tan-coloured predatory mite similar in size to TSSM and P. persimilis. While it feeds primarily on spider mites, it can survive for longer in their absence than P. persimilis, feeding on other insects such as thrips, other mites and pollen. Its advantage over P. persimilis is that it develops more quickly at higher temperatures, remains active and effective at temperatures above 30°C and is less affected by low humidities. Amblyseius californicus can be used simultaneously with the more specialized P. persimilis, but this latter predator is best used by itself under low population conditions or in «hot spots,» because A. californicus will also feed on P. persimilis.

Amblyseius fallacis — Similar in appearance to A. californicus, A. fallacis is a naturally occurring predatory mite in North American orchards. Likewise, it can survive in the absence of spider mites by feeding on other small insects and pollen. It has the benefit of remaining active and reproducing at lower temperatures than either P. persimilis or A. californicus. They can be used with other mite predators such as P. persimilis, Feltiella and Stethorus.

Feltiella acarisugaFeltiella is a gall midge, a small predatory fly that lays its eggs on leaves infested by spider mites. When the larva (Figure 18) emerges from the eggs, it feeds on all stages of mites. The adult midge is not predatory. Feltiella enters diapause under short day conditions and as such is only suitable for use from March to September.

Figure 18. Feltiella larva.

Stethorus punctillumStethorus is a small black ladybeetle (approx. 1.5 mm) (Figures 19 and 20) that feeds primarily on spider mites. Both adults and larvae are predatory. The adult is a good flier, locating spider mite infestations in the crops and laying eggs within the colony. This predator may not thrive on some host plants that have sticky hairs (e.g., tomato).

Figure 19. Stethorus adult.

Figure 20. Stethorus larva.

Cultural Control

Misting plants and raising the humidity will help suppress spider mite populations. For example, at 20°C and 36% relative humidity, a female TSSM will lay about seven eggs per day, while at 95% humidity, approximately 30% fewer eggs are laid.

Chemical Control

Because of their great reproductive potential, TSSM can quickly develop pesticide resistance. To effectively manage this pest using pesticides, observe these guidelines:

  • Direct sprays to the underside of leaves where spider mites usually congregate.
  • Be sure to achieve good coverage, particularly when using contact miticides such as Dyno-Mite, Floramite and Shuttle.
  • Use higher spray pressures to penetrate the web in areas of high mite density to reach the mites and the eggs within and beneath the web.
  • Use non-chemical control options as much as possible to minimize the development of pesticide resistance.

Broad mite/cyclamen mite

Observation of damage is usually the first indication of the presence of these mites. Know what the damage looks like and which crops are most susceptible to damage. Educate greenhouse workers so that any suspect plants are quickly brought to the attention of the grower or IPM manager. Early removal of infested plants or plant parts and good weed control inside and outside the greenhouse can slow the establishment and spread of these mites.

Various predatory mites are reported to feed on these mites, including Neoseiulus cucumeris, Amblyseius swirskii, A. californicus and A. andersoni. Neoseiulus cucumeris, A. californicus and A. swirskii have demonstrated effective suppression of broad mites on crops such as peppers and begonia in greenhouse studies. As with many pests, however, it is likely to be much more effective when the predatory mites are already in the crop prior to any infestation developing. If using biocontrol, apply higher numbers of predators in areas where damage is observed.

Pesticides can control broad mites and cyclamen mites, but not many pesticides are registered for their control in Canada and there is the potential for compromising biocontrol of other pests. Use pesticides with caution and check with the side-effects lists at sites such as Kopert and Biobest.

Tomato russet mite

As with broad mite and cyclamen mite, the first indication that growers usually have of their presence is when damage is observed. The mites disperse though the greenhouse on the hands, clothing and equipment of workers. When detected, take appropriate measures that could include removing plants or affected plant parts.

Predatory mites such as A. fallacis and A. swirskii may have some potential for managing tomato russet mite. One Ontario study indicated that several releases of high populations of A. swirskii on tomato plants, particularly at the «leading edge» of tomato russet mite infestations, can suppress spread of this mite on individual plants. However, it may be best to adopt an integrated approach that includes monitoring, registered biocompatible pesticides and releases of predatory mites on plants showing symptoms.

Ensure that there are no potential host plants in the greenhouse between crops. A thorough clean-up inside and outside the greenhouse will help reduce incidence and spread.


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