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Red spider mites on cannabis: How to spot and stop them
Red spider mites can destroy your grow before you even realise they’re there.
These microscopic pests thrive in hot, dry weather or conditions, multiplying at an alarming rate and sucking the life out of your plants.
Left unchecked, they’ll cause leaf discolouration, fine webbing, and severe plant damage, eventually leading to weakened growth, reduced yields, or even plant death.
The good news? You can stop them before they take over.
This guide covers how to spot red spider mites early, where they come from, and the best ways to get rid of them, naturally or with chemical treatments, so you can keep your cannabis plants healthy and thriving.
Disclaimer: Any information given on this site is for educational purposes only. Please ensure if you’re growing cannabis, you’re doing so by the law and subject to appropriate permissions and licenses of the applicable country.
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What are red spider mites?
The spider mite Tetranychus urticae, also known as the glasshouse red spider mite, is a microscopic arachnid that feeds on leaf cell contents, draining vital nutrients and leaving behind pale mottling.
This damage weakens your cannabis plants and, if left unchecked, can lead to severe plant stress, reduced yields, and can even kill your plants.
Despite the name, red spider mites and two-spotted spider mites are the same species.
Their colour varies depending on life stage and environmental conditions. In warm, active periods, they are yellowish green with two dark spots.
However, they turn red or orange in colder weather or during diapause (a resting state).
These pests are almost invisible to the naked eye, measuring less than 1mm.
To confirm an infestation, use a magnifying glass and inspect your plants, especially the underside of the leaves, where they gather to feed and lay eggs.
Where do red spider mites come from?
Red spider mites spread easily, hitching rides on infected plants, contaminated tools, or even your clothes.
If you grow outdoor plants, you’re more at risk, especially during late summer when high temperatures and low humidity create the perfect breeding conditions for the mites to wreak havoc.
They can also overwinter in plant debris, cracks in pots, or sheltered places, entering a winter resting period before re-emerging when the climate warms up.
Greenhouse plants are just as vulnerable, particularly if ventilation is poor and humidity is low.
How to identify red spider mites on cannabis
Since these common pests are hard to see, you’ll need to watch for signs of spider mite damage rather than looking for the mites themselves.
Here’s what to check for:
- Leaf discolouration – Pale mottling appears as tiny yellow or white specks on the upper surface of the leaf.
- Fine silk webbing – In large numbers, spider mites spin fine webs, often covering the underneath of the leaves and spreading across stems.
- Slowed plant growth – As mites feed, your cannabis plants become weak and struggle to grow.
- Eggs and tiny moving specks – Under a magnifying glass, you’ll see red spider mite eggs, egg shells, and small mites crawling on the plant.
Catching them early is key. If you spot fine webbing or spotted spider mites, act fast to prevent a heavy infestation.
What do red spider mites eat?
Red spider mites feed by puncturing the leaf surface and sucking out nutrients.
Their diet includes many susceptible plants, such as cannabis, edible crops, and various greenhouse plants.
By draining the plant’s strength, they cause leaves to turn yellow and drop prematurely. Over time, severe plant damage can lead to plant death, particularly in untreated infestations.
Preventing red spider mites on cannabis
The best defence against red spider mites is creating an environment where they can’t thrive.
Here’s how to make your grow space inhospitable to these pests.
Humidity & temperature control
Spider mites love hot, dry conditions. They reproduce fastest at 27°C and flourish in low humidity (20%).
Keep your relative humidity at 55 - 60% to slow their population growth and reduce the risk of an infestation.
Using a humidifier or misting your plants can help, especially during early flowering, when many growers drop humidity too soon.
Keeping your temperature below 25°C also limits their ability to spread.
Airflow & ventilation
Spider mites hate moving air. To prevent them from settling on your plants, maintain a steady airflow with oscillating fans.
Proper ventilation also helps prevent other issues, such as mould and mildew, ensuring your plants stay strong and resistant to pests.
Grow room monitoring
Using a grow room monitor or sensor lets you track humidity, temperature, and airflow in real time.
This data helps you fine-tune conditions and respond quickly to changes that could encourage spider mite infestations.
Keeping environmental factors within the ideal range not only prevents pests but also improves overall plant health and yields.
Smart feeding practices
Avoid overfeeding with nitrogen, as excess levels make plant sap sweeter and more appealing to spider mites.
Stick to a balanced feeding routine to keep your plants strong without attracting unwanted pests.
By fine-tuning your environmental conditions, you can significantly reduce the risk of a red spider mite infestation and ensure your plants stay healthy and pest-free.
Can you get rid of spider mites on cannabis?
Yes, you can get rid of spider mites on cannabis, but you need to act fast.
Increase humidity, introduce predatory mites like Phytoseiulus persimilis, and spray with neem oil, essential oils, or an insecticidal foliar spray.
For severe infestations, use mite control chemicals or uptake based insecticides.
Always remove infected plants and keep your grow space clean to prevent them from returning.
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How to get rid of a red spider mite infestation on cannabis
Once you’ve confirmed an infestation, you need to act quickly.
Spider mites reproduce fast, and a small infestation can turn into a large one in just days.
Here’s how to get rid of these pesky mites effectively and keep your cannabis plants healthy.
A. Natural red spider mite treatment
If you’re wondering how to get rid of red spider mites naturally, these treatment methods can help:
Increase humidity
Red spider mites thrive in hot, dry conditions, so raising humidity makes the environment less hospitable.
Using a humidifier or lightly misting your plants can slow their reproduction.
Introduce natural predators
Predatory mites like Phytoseiulus persimilis actively feed on spider mites, helping to reduce their numbers without chemicals.
Other predators or beneficial insects, such as ladybirds, can also help.
Neem oil and essential oils
Spraying with neem oil, plant oils, or a mix of fatty acids/insecticidal soap and foliar spray suffocates mites, disrupts their life cycle, and prevents them from laying more eggs.
Using neem oil during flowering is not advisable, as it can leave an unpleasant residue on buds, affecting their taste, smell, and overall quality. In some cases, it may even make the final product harsh to smoke.
If treatment is necessary during this stage, consider alternative methods like predatory mites or a gentle topical plant spray that won’t compromise your harvest.
Remove infected plantsIf you have a heavy infestation, carefully prune and dispose of affected plants to prevent the mites from spreading to healthy plants.
These methods work well for small infestations, but you may need stronger measures for large infestations.
B. Chemical red spider mite control
If the mites on your cannabis have spread significantly, you may need to use chemical methods:
- Systemic insecticide – The plant absorbs this treatment and kills mites as they feed on treated leaves.
- Biological control – Some red spider mite treatments use targeted chemicals that kill spider mites but don’t harm pollinating insects or natural predators like predatory mites.
Whichever method you choose, always monitor mite numbers, check the underside of the leaves, and reapply treatments if necessary to fully eliminate the spider mite population.
Avoid future infestations
Here’s how to control red spider mites and stop them from returning:
- Inspect new clones – Always check new clones for signs of mites before introducing them to your grow space.
- Remove plant debris – Clear away old canes, plant ties, and infested plants to eliminate hiding spots.
- Maintain humidity – Avoid low humidity, which encourages mites. Instead, increase humidity slightly to make conditions less favourable.
- Encourage predatory mites – Keeping a population of red spider mite predators can help keep spider mite populations in check.
By staying vigilant, you can keep your cannabis plants free from these common pests.
Takeaways
Red spider mites can be a serious threat, but with early detection and the right red spider mite control methods, you can get rid of the mites and prevent future outbreaks.
Whether you choose biological control, beneficial insects, or red spider mite treatment with neem or chemicals, taking swift action is key.
Keep your grow area clean, monitor for signs of spider mite damage, and maintain high humidity to reduce the risk of an infestation.
By following these steps, you’ll protect your cannabis plants and ensure they stay strong, healthy, and pest-free.
Happy growing!
FAQs
Are red spider mites harmful to humans?
No, red spider mites are not harmful to humans. They don’t bite or spread disease. However, they can devastate plants, making keeping on top of them essential for maintaining a healthy grow.
How do I get rid of red spider mites?
To get rid of glasshouse red spider mites on plants, act fast.
First, increase humidity, they thrive in hot, dry conditions. Introduce predatory mites like Phytoseiulus persimilis for biological control. Spray affected plants with neem, essential oils, or insecticidal soap to disrupt their life cycle.
For severe infestations, use chemicals or an uptake based insecticide.
Always remove infected plants and keep your grow space clean to prevent reinfestation.
What can I spray to get rid of red spider mites?
To get rid of cannabis red spider mites, spray your plants with neem, essential oils, or a fatty acid-based leaf application.
These treatments disrupt their life cycle. Neem isn’t appropriate for use during flowering, though.Use red spider mite control chemicals or an insecticide for a stronger approach.
Always spray the underside of the leaves, where mites hide and lay eggs.
What kills spider mites instantly? Neem, insecticidal soap, and fatty acid-based foliar mists also work quickly by suffocating mites. Systemic insecticides provide fast results for severe infestations.
Always spray the underside of the leaves, where mites hide, and repeat treatments to eliminate eggs and newly hatched mites.Want to grow like a pro?
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