by Ben Morris, Head Breeder of Dirty Bird Genetics
Introduction:
There is a plethora of pests that plague our gardens, green houses, and grow spaces but few can compete with the rapidity and malignancy of the two-spotted spider mite (Tetranychus urticae). Two-spotted spider mites are small, herbivorous arachnids that feed on plant sap and chlorophyll by puncturing the underside of leaves with their tiny, piercing mouth parts called ‘chelicerae’.1 This feeding mechanism causes damage to the leaf which hinders the overall photosynthetic ability of the infested plant. These pests can reproduce rapidly and, if left untreated, can quickly lead to the deterioration, and ultimately, the death of an infected plant. The damage caused by two-spotted spider mites can lead to lower flower yields, seed abortion, and improper seed fill. This is a huge detriment for flower producers as well as for breeders and seed producers. These voracious little creatures are tiny (between 1/80th and 1/50th of an inch)2 and can be very difficult to detect before moderate to heavy infestation occurs. In the following sections, we will go through some of the visual signs growers can use to determine if they have a spider mite infestation and what approximate level that infestation is likely at (low, moderate, high).
Identification/Plant Signs:
As previously stated, two-spotted spider mites (TSM) are very small. Fully grown adult spider mites will appear as whitish to grayish-green specks with eight tiny legs and two dark spots on either side of their body. They are easy to mistake for small pieces of dirt of other, non-living debris but if you watch them long enough you will see them scurry about. They are largely found on the abaxial (underside) surface of leaves where they take advantage of any nooks and crannies they can find to hide and feed in. Having a hand magnifying glass or a jeweler’s loupe will make identifying these pests much easier than trying to observe them with your naked eye.
Early into infestation there are few signs of the two-spotted spider mite, the main indicator being the observation of the mites themselves. One can inspect a plant or clone they are obtaining using a jeweler’s loupe, or other hand magnification tool, to check under the leaves and on the stems for small whitish, gray/green bodies that often exhibit two large dark spots on both sides of the idiosoma3 (the main part of the body). One single female TSM can cause an infestation due to their rapid reproduction cycle and their ability to reproduce asexually. Thoroughly inspecting any incoming plants to your grow space is paramount in detecting pest issues. If there is a spider mite, or if there are multiple, inhabiting the plant’s aerial parts without any signs of insect feeding damage on the leaf and without webbing present, the plant is in the early stages of infestation.
As they feed, they pierce and damage leaf cells which ultimately leads to the desiccation and the eventual death of the cells they feed upon. This can eventually lead to the death of the entire leaf which obviously harms the plant. A sign of their feeding includes tiny, lightly colored dots that are observable on the adaxial surface (upper side) of leaves. These dots can appear whitish, yellow, or silver and give the leaf a mottled appearance. These damaged leaves can take on a yellow/gray or even bronze appearance as the damage spreads. If you see small, dotted patterns (also known as stippling) occurring on your leaves, check the underside of those leaves for the small, oval bodies of two-spotted spider mites.4
If the spider mites are left alone, they will continue to work their way up the plant, leaving visual indications via stippling/mottling on more leaves higher and higher into the canopy of the plant. Lower leaves, or leaves first infested, will begin to turn yellow and may start falling off. Eventually, when they reach a certain population size they will begin to make webs. These webs look just like spider webs and help the mites to protect themselves from predators as well as act as highways between plants for easier access to new feeding grounds.
Two-spotted spider mites focus on feeding and reproduction before they focus on making webs.5 This is good to know as it can help a grower determine what level of infestation they are dealing with. Below is a rough guide to determining the level of infestation and what action may be necessary. This rating scale was adapted from the work of Bruce Potter and Ken Ostlie6 (University of Minnestoa)
No Infestation: No spider mites nor plant injury observed.
Low Infestation: Minor stippling or mottling on lower leaves, no premature leaf yellowing observed
Low-Moderate Infestation: Stippling or mottling common on lower leaves; some premature yellowing observed
Moderate Infestation: Heavy stippling/mottling on lower leaves progressing into middle canopy; leaf yellowing and leaf loss observed; mites observed in middle and top canopy
Moderate-High Infestation: Lower leaf yellowing very apparent and leaf loss common; stippling/mottling, webbing, and mites common in middle canopy; mites and minor stippling/mottling in upper canopy
High Infestation: Lower leaf loss common and yellowing into middle canopy; stippling/mottling and distortion of upper leaves common; mites in upper canopy; webbing in upper canopy
Treatment:
The damage caused to leaves by two-spotted spider mites is not reversible2 so prevention, early detection, and treatment are of the utmost importance in ensuring your crop’s health and productive capacity.
There are many options available for treating spider mite infestations that largely reside within three categories: Physical, Chemical, and Biological.
Physical Controls:
Earlier into infestation a grower can use a hose or other means of spraying water with adequate pressure on the undersides of the leaves of their plant to physically knock the spider mites off of the undersides of the leaves. This method is not appropriate to use if mold is an issue in your grow space but can work for some growers in initially removing the mites. The drawback to this approach, besides a potential in increased mold presence, would be that mites not killed by being sprayed off could climb back up the plant and re-infest.
Some growers have had success in wiping their leaves down physically with a cloth and a small amount of insecticidal soap or oil. This can physically remove and crush mites and mite eggs but is time consuming and can lead to leaf damage if not done with care.
In early stages of infestation, removing heavily infested leaves and disposing of them immediately outside of your grow space can help to reduce the mite’s numbers as well.
Chemical Controls:
If the infestation becomes moderate or high, then chemical controls may have to be employed. Pyrethrins can be effective in killing mites but should be avoided due to the natural mite predators they also kill, which can lead to a TSM population resurgence.7 Pyrethrin should not be used during the mid to late flower stage of the cannabis growth cycle as it can be hard, if not impossible, to wash these chemicals from the flower/plant.8 Earlier in the flowering stage and/or during the vegetative stage pyrethrins can be somewhat effective in suppressing mite populations. Take care not to employ pyrethrins if you have adequate mite predators in and around your plants as these chemicals can also kill the beneficial insects, as previously stated.
Neem oil can also be used in a spray to knock adult mites off of leaves and the residue from the neem oil will suffocate the mite eggs, interrupting their life cycle and denying much of the next generation from being able to colonize and feed on your plants.4
There are organic chemical treatments that often employ some mixture of rosemary, clove, and mint oils to deter and repel mites. Many products are offered with these ingredients and can be used in foliar sprays as well as in the water the plants are fed to increase the amount of these substances in the soil and plant to further deter mites.9,10
Some growers have reported success with using a mix of isopropyl alcohol and water at a 1:9 ratio. This mixture can be used as a foliar spray to knock mites off the leaves and to also kill them. Isopropyl alcohol will also kill the mite eggs as well, attacking multiple generations of the mites at once. There are precautions to be taken if employing this method as isopropyl alcohol, if not diluted enough, can damage plant tissue as well. It also can dry leaves out if the temperature is high (80 degrees F and above). If employing this method it is best to test the spray on a few leaves first to see how the plant will respond before spraying the entire plant. It is recommended to spray near the end of the day to avoid the isopropyl alcohol sitting on the leaves and causing burning damage. While this method can be effective we do not recommend it unless no other options are available due to the risk of further plant damage but we wanted to include it as an option due to some positive reports from other growers.11
Insecticidal soaps can also be employed to kill and remove mites from plants. As with any insecticide, read the label that comes with the product and apply according to the manufacturer’s instructions to avoid any unnecessary plant damage.
Sucrose octonoate esters have been proven to be very effective in killing two-spotted spider mites, as well as other mite species and even aphids.12 One such product, Organishield, is made with these substances and, when applied as a foliar spray to the undersides of plant leaves, can kill juvenile and adult mites on contact by drying the waxy, protective cuticle that envelops them. Once this waxy cuticle is dried out it can lead to rapid dehydration and desiccation of the mites which leads to their death. Sucrose octonoate ester treatments are very environmentally friendly as they are non-toxic to humans, other animals such as pets, and they do not harm pollinators such as bees. Sucrose octonoate esters also have very low toxicity to aquatic life making them a very safe option for treatment. Sucrose octonoate esters also degrade rapidly (usually within 5 days) and only leave behind water, CO2, fatty acids, and sucrose so there is no lasting environmental impact such as with other, more toxic chemical treatments.
For light to moderate infestations a mix of 60ml Organishield per gallon of water, when applied in a foliar spray to the undersides of leaves, can be very effective in reducing the level of infestation and killing large numbers of mites. For heavier infestations a mix of 80ml Organishield per gallon of water is recommended by the manufacturer to lead to a faster kill on contact. After years of use we can personally vouch for this method of treatment as we have seen it to be very effective in reducing mite infestations while not harming our plants nor exposing our workers or the environment to toxic substances. As with any foliar spray treatment, remember to turn off grow lights during spraying to not potentially burn plants due to the magnification of light through water droplets.
Many of the substances discussed above will only act upon TSM nymphs and adults, not their eggs. We recommend applying another spray 3-7 days after the initial treatment to ensure the removal of newly hatched spider mites. For severe infestations, a treatment every 3-5 days (depending on insecticidal substance used; consult the manufacturer’s label) can be beneficial in continuously killing newly hatched two-spotted spider mites.
Biological Controls:
There are many biological and environmental (cultural) controls that can be employed in lieu of or in addition to physical and chemical treatments.
One common route is to employ predators of the two-spotted spider mite in your grow space. There are many species of insects and arachnids that predate on two-spotted spider mites and utilizing these species can be immensely helpful in combating mite infestation without the need for chemical treatment.
One such species, Phytoseiulus persimilis, is another kind of mite and a specialized hunter of two-spotted spider mites. P. persimilis can eat many adults and even more young two-spotted spider mites in a day. These can be purchased from several suppliers and then spread onto the infested plants. P. persimilis only eats two-spotted spider mites so they can be very effective in decimating TSM populations but will die off once their food source is depleted. These predatory mites are generally seen as good for rapid treatment when infestation levels are moderate to high.13
Neoseiulus californicus is another predator mite that has shown a decent effectiveness towards reducing spider mite populations. N. californicus has been reported to be hardier and able to survive hotter and drier temperatures than P. persimilis making it a good choice for growers with hot, dry grow area conditions. N. californicus can be used as a preventative measure as they have a wider range of prey they hunt and consume than just the two-spotted spider mite and thus may survive longer eating other pests in addition to TSM’s.13
Neoseiulus fallacis is a predatory mite that is more effective in cooler (50 – 800F), temperate climates and for outdoor grows as it has the ability to overwinter if enough food is present. By avoiding spraying chemical treatments and keeping N. fallacis populations alive and undisturbed some growers have been able to see this predator return the next year to continue hunting and eating two-spotted spider mites as well as other mite species and even some small arthropods.13
Ladybugs (of the family Coccinellidae and also known as lady-beetles) can also be used for mite control but aren’t the most effective at such a task due to their penchant for spreading out and away from grow areas as well as their preference for larger prey like aphids as opposed to two-spotted spider mites. However, there is a species of lady-beetle that is known as the “spider mite destroyer” scientifically named Stethorus punctillum that does hunt smaller insects and arachnids such as the two-spotted spider mite. These lady-beetles can also be applied to infested plants to hunt and reduce not only two-spotted spider mites, but a range of different mite species and even aphids. S. punctillum prefers spider mites for its diet but will eat aphids and mite eggs if juvenile/adult spider mites are not present making S. punctillum a good potential predator for integrated pest management. Unlike other, larger ladybug species, S. punctillum will not immediately disperse from the area as long as their food source is present making them good candidates for long term protection against plant pests, especially in green houses.14
The green lacewing (of the family Chrysopidae) is another species of insect that can be used effectively to treat spider mite and aphid infestations. While normally used more for aphid control, green lacewing larvae are voracious predators of smaller herbivorous insects and arachnids. Green lacewing larvae can be spread on the soil as well as on the leaves of a plant and left alone to hunt and eat many pests that threaten the health of your garden. If conditions are right (e.g. 68-900F temperatures, adequate pests for larvae to feed on, adequate flowering plants that produce nectar for adults to feed on) then a green lacewing population can be maintained throughout several growing seasons for lasting pest protection. Although the adult green lacewing is an herbivore it will not feed directly on cannabis plants and prefers nectars and pollen from flowering plants such as coriander, dill, or fennel, among others. Having any of these species as companion plants in your grow area can help to encourage lacewing population growth and can maintain their presence in your grow area.15
With any pest predators a grower should be careful about applying broad-spectrum insecticides as these can kill the beneficial insects you spent time and money on attracting and/or introducing to your grow space.
TSM Life Cycle/Prevention:
Two-spotted spider mites have 5 essential parts of their life cycle: Egg – Larvae- Protonymph- Deutonymph-Adult. Adult TSM’s usually live for 2-4 weeks and feed continuously on plant sap and chlorophyll from punctured leaf surfaces. Female TSM’s can lay anywhere from 2 – 20 eggs a day, with a rough average of 10-15 eggs laid a day in favorable conditions. Females will lay eggs regardless of whether male mites are present or not. Any unfertilized eggs will hatch as males, which will then fertilize the next batch of eggs to create more females.2,5 With this knowledge in mind, it is easy to see how even a single female TSM can start an outbreak that can take over your garden or grow space in very little time.
Two-spotted spider mites thrive in environmental conditions where it is hot, dusty, and dry. Between 68-860F, the spider mite life cycle can be completed in as little as 7-8 days, which means eggs have been laid-larva hatched-two nymph phases completed-and adult maturation achieved with another round of egg laying and fertilization occurring in about a week’s time. TSM’s optimal breeding and life cycle occurs also when relative humidity is less than 50%. 16
These temperature and humidity parameters can make environmental conditions difficult to balance as the low RH discourages mold and fungal growth but invites the presence of mites. The temperature range for optimal mite population growth also encompasses the temperature range for optimal cannabis growth (70-850F).
There are cultural controls that can be employed to reduce mite populations and breeding rates:
- Make sure your plants are adequately watered. Drought stress invites mites to feed upon your plant so making sure it has enough water will aid in not attracting TSM’s to it. 4, 16
- Raise the RH of your grow space to 60%. This will still allow for reduction and suppression of mold growth while slowing the breeding rates of mites at the same time.
- Avoid over-fertilization with nitrogen, which can encourage the soft, succulent growth that attracts mites.17
- Limit the amount of dust around your plants as dust can protect mites from predators. Using mulch to suppress dust in outdoor grows can be helpful. Sprinkler systems in outside grows can also help to reduce the amount of dust present on and around plants.
- Keep your grow-spaces CLEAN. Remove leaf litter and other biological debris that could act as vectors for mold and hiding places for mites. Remove heavily infested leaves and discard them far from the grow area as soon as possible.
- Reduce plant stress in any way you can. Stressed plants are much more susceptible to attack from mites, as well as many other pests. By keeping your plants healthy and happy you give them a better chance at not attracting mites in the first place.18
- Feeding plants with potassium silicate can help to strengthen the cell walls of the plant, making it more difficult for mites, and other piercing insects, to puncture leaf and stem surfaces.19
Disclaimer:
This publication may contain pesticide recommendations that are subject to change at any time. These recommendations are provided only as a guide. It is always the pesticide applicator's responsibility, by law, to read and follow all current label directions for the specific pesticide being used. Due to ever-changing labels and product registrations, some of the recommendations given in this writing may no longer be legal by the time you read them. If any information in these recommendations disagrees with the label, the recommendation must be disregarded. No criticism is intended for products not mentioned. The author(s), Dirty Bird Genetics, and North Atlantic Seed Company assume no liability resulting from the use of these recommendations.
References:
1 Owens, D., Stubbs, C. (10/2024). Two Spotted Spider Mite. University of Delaware.
"https://www.udel.edu/academics/colleges/canr/cooperative-extension/fact-sheets/two-spotted-spider-mites/
2 Two-spotted Spider Mites (Soybean) Tetranychus urticae Koch. (n.d.). Purdue University. Retrieved 02/2026
3 Fasulo, T.R., Denmark, H.A. (n.d.). Twospotted Spider Mite, Tetranychus urticae Koch (Arachnida: Acari: Tetranychidae). Askifas. Retrieved 02/2026.
https://ask.ifas.ufl.edu/publication/IN307
4 Hahn, J., Wold-Burkness, S. (n.d.). Twospotted spider mites in home gardens. University of Minnesota. Retrieved 02/2026.
https://extension.umn.edu/yard-and-garden-insects/spider-mites
5 Godfrey, L.D. (12/2011). Spider Mites: Integrated Pest Management for Home Gardeners and Landscape Professionals. University of California.
https://ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnspidermites.pdf
6 Potter, B., Ostlie, K. (n.d.) Managing spider mite on soybean. University of Minnesota Extension. Retrieved 02/2026.
https://extension.umn.edu/soybean-pest-management/managing-spider-mite-soybean
7 Agriculture: Cotton Pest Management Guidelines: Webspinning Spider Mites. (n.d.). UC IPM. Retrieved 02/2026.
https://ipm.ucanr.edu/agriculture/cotton/webspinning-spider-mites
8 Harmful Effects of Pesticide Residue in Cannabis. (July 15, 2024). Encore Labs.
9 Mossa, A.T.H., Afia, S.I., Mohafrash, S.M.M., Abou-Awad, B. (01/2019). Rosemary essential oil nanoemulsion, formulation, characterization and acaricidal activity against the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae). Research Gate.
10 Mahmoud, R.H., Kassem, E.M.K. (02/2022). Laboratory and Semi - Field Evaluation and Effect of Clove Essential - Oil against Two - Spotted Spider - Mite Tetranychus urticae, Koch. (Acari:Tetranychidae) Journal of Plant Protection and Pathology, Vol 13 (Issue 2) Pgs 59-61
11 Loughrey, J. (n.d.). How to Identify and Control Spider Mites on Plants. Garden Design. Retrieved 02/2026.
https://www.gardendesign.com/how-to/spider-mites.html
12 Puterka, G. (09/2010). Sugar Ester Compounds for Arthropod Control. U.S. Dept. of Agriculture. Retrieved 02/2026.
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