Spider Mites on Cannabis: How to Identify, Treat & Prevent an Infestation

Spider mites are one of the most destructive and frustrating pests a cannabis grower can face. These tiny arachnids can devastate a healthy crop in a matter of days, and because they reproduce so rapidly, a small infestation can quickly spiral out of control. Whether you're a first-time grower or a seasoned cultivator, knowing how to identify, treat, and prevent spider mites on cannabis is essential knowledge for protecting your plants.

What Are Spider Mites?

Spider mites (most commonly Tetranychus urticae, the two-spotted spider mite) are tiny arachnids — not insects — that feed on plant cells by piercing the leaf surface and sucking out the chlorophyll-rich contents. In cannabis grow rooms, they thrive in warm, dry conditions with poor airflow. A single female can lay up to 200 eggs over her two-to-four-week lifespan, which means infestations grow exponentially if left untreated. Under ideal conditions (above 26°C with low humidity), spider mite populations can double every two to three days.

How to Identify Spider Mites on Cannabis Plants

Early detection is critical. Spider mites are approximately 0.5mm in size — nearly invisible to the naked eye. Here's what to look for:

Early Stage Signs

• Tiny white or yellow dots (stipples) on the upper leaf surface — these are feeding puncture marks
• Pale, faded, or dusty leaf texture — leaves lose colour and take on a bleached or silvery appearance
• Tiny moving dots on leaf undersides — adult mites appear reddish, brown, or pale

Advanced Stage Signs

• Fine silk webbing between leaves and stems — a sign of a significant established infestation
• Yellowing and browning leaves — heavily infested leaves die and drop rapidly
• Stunted plant growth — yields are significantly impacted as mites drain cell nutrients

The Best Tool for Early Detection

Because spider mites are so small, a magnifier is the single most effective way to catch an infestation early. Keep an Illuminated Magnifier Loupe in your grow room for routine inspections. For detailed examination of mites, eggs, and feeding damage, the Illuminated Microscope (60x–100x) gives you exceptional clarity.

Pro tip: Inspect plants at least twice per week, focusing on leaf undersides where mites congregate and lay eggs.

The Spider Mite Life Cycle: Why They're So Hard to Eliminate

Spider mites go through five life stages: egg, larva, protonymph, deutonymph, and adult. The full cycle can complete in as few as 5–7 days in warm conditions. This is why a single missed treatment window allows the population to recover and re-explode. Any effective treatment plan must run for multiple cycles to eliminate all life stages — particularly eggs, which are highly resistant to most sprays.

How to Treat Spider Mites on Cannabis

Once you've confirmed a spider mite infestation, act immediately. The longer you wait, the harder they are to eliminate.

Step 1: Isolate Affected Plants

Quarantine any visibly affected plants immediately to prevent spread. Spider mites move between plants easily, especially when leaves make contact.

Step 2: Physically Remove Mites and Webbing

Gently wipe down affected leaves with a damp cloth to physically remove mites, eggs, and webbing before applying spray. This step reduces the population and improves spray penetration.

Step 3: Apply a Targeted Spray Treatment

Apply an organic pesticide spray to all leaf surfaces, paying particular attention to undersides where mites and eggs hide. Our Spidermites Spray by Buddi Sprays is a locally made, organic formulation developed specifically for cannabis and garden plants. Available in 200ml and 500ml sizes. For broader pest coverage, the All Rounder Spray by Buddi Sprays targets spider mites alongside aphids, whitefly, and other common grow room pests.

Step 4: Repeat Every 3–4 Days for 3 Cycles

Spider mite eggs are highly resistant to treatment. A single application kills active adults and nymphs but leaves eggs intact. Treat every 3–4 days for at least 3 full cycles to target newly hatched mites before they can reproduce.

Step 5: Verify with a Magnifier

After each treatment cycle, inspect under an Illuminated Magnifier Loupe to confirm populations are declining. If active mites persist after three treatments, switch products to prevent resistance building.

How to Prevent Spider Mites in Your Grow Room

Control Temperature and Humidity

Spider mites thrive in hot, dry conditions. Keep your grow room between 20–26°C and maintain relative humidity above 50%. Spider mite reproduction slows significantly at higher humidity levels.

Maintain Strong Airflow

Good air circulation disrupts mite movement and makes it harder for them to establish colonies. Ensure adequate oscillating fans throughout your grow space.

Quarantine New Plants and Clones

Never introduce new plants or clones directly into your main grow space without a 1–2 week quarantine. This is one of the most common ways spider mites enter a clean grow room.

Use Preventative Sprays

Apply the Buddi All Rounder Spray as a preventative measure during the vegetative stage. Do not apply during late flowering to protect your final product.

Spider Mites During Flowering: What to Do

• Early flowering (weeks 1–4): Spray treatments can still be applied safely. Avoid direct contact with developing buds.
• Late flowering (weeks 5+): Spraying risks affecting bud quality. Focus on physical removal and increasing humidity and reducing temperature instead.
• Final weeks: If the infestation is severe and harvest is imminent, consider harvesting early to save what you can.

Frequently Asked Questions About Spider Mites on Cannabis

Can spider mites survive between grows?

Yes. Spider mites survive in dead plant material, growing medium, and on grow room surfaces. Always thoroughly clean and sanitise your grow space between cycles.

How quickly do spider mites spread?

Under optimal conditions, a spider mite population can double every 2–3 days. A small infestation can become severe within 1–2 weeks if left untreated.

Are spider mites visible to the naked eye?

Adult spider mites are barely visible at around 0.5mm. Their webbing and the stippling damage on leaves are the most reliable visible indicators without magnification. An Illuminated Magnifier Loupe makes early detection significantly easier.

What temperature kills spider mites?

Spider mites are killed by temperatures above 40°C — far too hot for cannabis plants. Cold temperatures below 10°C slow reproduction significantly but don't eliminate them.

Shop Spider Mite Control at Skyline Smoke Company

• Spidermites Spray by Buddi Sprays — Targeted organic treatment for spider mite infestations
• All Rounder Spray by Buddi Sprays — Multi-pest preventative and treatment spray
• Illuminated Magnifier Loupe — Essential tool for early mite detection
• Illuminated Microscope (60x–100x) — High-magnification grow room inspection tool

Catching spider mites early is the key to protecting your crop. Regular inspection combined with a consistent preventative spray routine will keep your grow room clean and your plants healthy from seed to harvest.