Red spider mites—often called spider mites in Dutch—are one of the most dangerous and common pests in cannabis cultivation. These tiny creatures can destroy an entire harvest in a short time if not treated quickly and effectively.
🔍 What is red spider mite?
The red spider mite (Tetranychus urticae) is a microscopic mite that feeds on the sap of cannabis leaves. To the naked eye, they often appear as small reddish-brown dots, usually on the underside of the leaves.
Each female spider mite can lay up to 100 eggs per week, causing the population to grow rapidly—especially in warm, dry environments (25–30 °C, low humidity).
🌿 How red spider mites attack your plants
The damage is caused by spider mites sucking up chlorophyll. This weakens the plant, stunts growth, and significantly reduces yield.
Symptoms of infection:
Small yellow or white dots on the leaves.
Leaves become dull, dry or curl inwards.
Fine spider webs between leaves or buds.
Reduced growth and leaf drop.
In case of severe infestation: plants appear “burned out”.
⚠️ Why spider mites are so dangerous in cannabis
They multiply rapidly, especially at high temperatures.
They are hard to see until it's too late.
They are becoming resistant to many chemical pesticides.
They can spread quickly via clothing, tools or air currents.
🧪 Preventing red spider mites
Prevention is much easier than cure. With a few simple measures, you can avoid an infection:
- Hygiene is essential
Clean the growing area and tools regularly.
Wear clean clothes when entering the room.
Do not allow pets or other plants nearby.
- Check new plants
Every new plant can bring eggs or mites. Check under the leaves with a magnifying glass before placing them in the growing space.
- Keep the climate humid
Spider mites hate moisture!
Keep humidity between 55–65°C (55–65°F) during growth.
Mist the leaves with water occasionally (but not during the flowering phase to avoid mold).
- Good air circulation
Fans prevent warm, dry areas where spider mites multiply quickly.
🧤 Natural pest control methods
If spider mites do appear, it is best to use organic methods to save your plants without residue or damage.
🐞 1. Predatory mites (Phytoseiulus persimilis)
These beneficial insects eat red spider mites and can eliminate an infestation within a few weeks. They work best at 20–28°C and a humidity of 60%.
🌿 2. Neem oil
A natural oil from the neem tree that suffocates spider mites and stops their reproduction.
Mix 1–2 ml of neem oil per liter of water.
Spray under and above the leaves (not in full bloom).
🍃 3. Insecticidal soap or potassium soap
Kills spider mites on direct contact.
Repeat every 3 days until the infestation is gone.
🌸 4. Essential oils (mint, rosemary, eucalyptus)
Can repel spider mites as a preventative spray.
🚫 What you better not do
Don't use harsh chemical pesticides during the flowering stage — they can leave toxic residues on your buds.
Avoid extreme heat or cold to kill spider mites: this will also harm the plant.
🔄 Recovery after an infection
After a plague:
Remove and destroy severely affected leaves.
Clean the entire grow space with alcohol or bleach solution.
Disinfect pots, fans and tools.
Replace filters and check air intakes.