Cannabis Pests: Identify & Eliminate
Bugs in your grow? Act fast. Pest populations explode exponentially—what starts as a few spider mites becomes thousands in days. This guide helps you identify common cannabis pests and eliminate them before they destroy your harvest.
Quick Answer: Most Common Pests
The Big 5 cannabis pests: Spider mites (tiny dots + webs), thrips (silver streaks), fungus gnats (small flies near soil), aphids (clusters on stems), and whiteflies (tiny white moths). All can be treated with neem oil during veg. Act within 24-48 hours of detection!
Quick Navigation
| Pest | ID Signs | Damage | Best Treatment |
|---|---|---|---|
| Spider Mites | Tiny dots, fine webs, yellow speckles | Severe—can kill plants | Neem oil, predatory mites |
| Thrips | Silver streaks, tiny slender bugs | Moderate—stunts growth | Spinosad, neem oil |
| Fungus Gnats | Small flies near soil, larvae in soil | Low-moderate (larvae eat roots) | Let soil dry, BTi, sticky traps |
| Aphids | Clusters on stems, sticky residue | Moderate—spread disease | Neem oil, ladybugs |
| Whiteflies | Tiny white moths, fly when disturbed | Moderate—weaken plants | Sticky traps, neem oil |
Spider Mites: The Most Destructive Pest
Spider mites are the #1 threat to indoor cannabis grows. These microscopic arachnids reproduce explosively—a single female can produce millions of offspring in a month. By the time you see webbing, you have a severe infestation.
Identification
- Size: Nearly microscopic (0.4mm)—look like moving dots
- Location: Undersides of leaves (always check there first!)
- Signs: Yellow/white speckles on leaves, fine webbing, leaves turning bronze
- Test: Shake a leaf over white paper—moving dots = mites
Treatment
- Isolate infected plants immediately
- Remove heavily infested leaves (bag and dispose outside)
- Spray entire plant with neem oil or insecticidal soap—tops AND undersides of leaves
- Repeat every 3-5 days for at least 2 weeks (to kill newly hatched eggs)
- Raise humidity above 60%—mites thrive in dry conditions
- For severe infestations: introduce predatory mites (Phytoseiulus persimilis)
Critical: Treat ALL Plants
Spider mites spread via air currents, clothing, and pets. If one plant has them, assume all do. Treat your entire grow space—not just visibly infected plants. Missing even a few mites means the infestation returns in days.
Thrips: The Silver Streak Makers
Thrips are tiny, slender insects that scrape leaf surfaces and suck out the contents. They're harder to spot than mites but leave distinctive silver/bronze streaks on leaves.
Identification
- Size: 1-2mm, slender, yellowish-brown
- Signs: Silver/bronze streaks or scratches on leaves, tiny black dots (feces)
- Movement: Jump/fly when disturbed
- Check: Gently shake leaves over white paper
Treatment
- Apply spinosad spray (organic, very effective against thrips)
- Alternative: neem oil or insecticidal soap
- Use blue sticky traps (thrips are attracted to blue)
- Introduce predatory insects: minute pirate bugs, lacewings
- Repeat treatments every 5-7 days for 2-3 weeks
Fungus Gnats: The Overwatering Indicator
Fungus gnats are more annoying than destructive, but their larvae eat roots. They're a clear sign you're overwatering. The adults are harmless—it's the larvae in the soil that cause problems.
Identification
- Adults: Small black flies (2-3mm) hovering near soil surface
- Larvae: Tiny translucent worms in top inch of soil
- Behavior: Fly up when you water or disturb soil
Treatment
- Let soil dry completely between waterings—this kills larvae
- Place yellow sticky traps near soil to catch adults
- Add 1" layer of sand, perlite, or diatomaceous earth on soil surface
- Apply BTi (Bacillus thuringiensis israelensis) to soil—kills larvae specifically
- Water with diluted hydrogen peroxide (1:4 H2O2:water) to kill larvae
Aphids: The Clustered Sap-Suckers
Aphids cluster on stems and new growth, sucking sap and weakening plants. They're easy to see (2-4mm) and come in various colors: green, black, brown, or white. They also spread viral diseases between plants.
Identification
- Appearance: Soft-bodied, pear-shaped, 2-4mm
- Location: Clustered on stems, under leaves, on new growth
- Signs: Sticky honeydew residue, curled leaves, black sooty mold
Treatment
- Blast with water to knock off (outdoors or over sink)
- Spray with neem oil or insecticidal soap
- Release ladybugs (each eats 50+ aphids per day)
- For severe infestations: pyrethrin spray (last resort)
Whiteflies: The Tiny White Moths
Whiteflies look like tiny white moths and fly up in clouds when plants are disturbed. Like aphids, they suck sap and excrete sticky honeydew.
Identification
- Appearance: Tiny (1-2mm) white, moth-like insects
- Behavior: Fly up in a cloud when plant is disturbed
- Location: Undersides of leaves
Treatment
- Yellow sticky traps near plants (very effective)
- Neem oil spray every 5-7 days
- Insecticidal soap directly on insects
- Introduce parasitic wasps (Encarsia formosa)
Prevention: Keep Pests Out
Prevention is infinitely easier than treatment. Once pests establish, eradication is difficult and stressful. Build these habits:
- Quarantine new plants for 2 weeks before introducing to your grow
- Change clothes after visiting other grows or garden centers
- Keep grow area clean—remove dead leaves, debris
- Maintain airflow—pests thrive in stagnant conditions
- Inspect regularly—check leaf undersides weekly with magnification
- Use HEPA filters on intake vents
- Don't overwater—wet conditions attract gnats and mold
Treatment Options Comparison
| Treatment | Organic? | Use in Flower? | Best For |
|---|---|---|---|
| Neem Oil | ✅ Yes | ❌ No | Most pests in veg; prevention |
| Insecticidal Soap | ✅ Yes | ⚠️ Early only | Soft-bodied insects (aphids, mites) |
| Spinosad | ✅ Yes | ⚠️ Early only | Thrips, caterpillars, leaf miners |
| BTi | âś… Yes | âś… Yes | Fungus gnat larvae specifically |
| Predatory Insects | âś… Yes | âś… Yes | Long-term control, all stages |
| Pyrethrin | Mostly | ❌ No | Last resort—severe infestations |
Warning: Avoid Pesticides in Late Flower
During the final 2-3 weeks of flowering, avoid spraying anything on buds—residues affect taste and safety. If pests appear late in flower, remove affected buds and increase airflow. Prevention before flowering is critical.
Frequently Asked Questions
What are the tiny white bugs on my cannabis?
Usually spider mites, whiteflies, or thrips larvae. Spider mites are most common—check for fine webbing and yellow speckles. Whiteflies fly up when disturbed. Thrips are elongated. All can be treated with neem oil in veg.
How do I get rid of spider mites?
1) Remove infested leaves. 2) Spray neem oil/insecticidal soap every 3-5 days for 2 weeks. 3) Raise humidity above 60%. 4) For severe cases, use predatory mites. Treat ALL plants—mites spread fast.
What causes fungus gnats?
Overwatering. Gnats thrive in wet soil with decaying matter. Fix by letting soil dry completely, using yellow sticky traps, and applying BTi (Bacillus thuringiensis) to kill larvae in the soil.
Can I use neem oil during flowering?
No—it leaves bad taste/smell on buds. Only use neem during veg. In flower, use alternatives like spinosad (early flower only), insecticidal soap with rinse, or predatory insects. Best strategy: eliminate pests before flowering begins.
What are silver streaks on my leaves?
Thrips damage. These tiny insects scrape leaves and suck out contents, leaving silver/bronze trails. Check undersides of leaves for slender, moving insects. Treat with spinosad or neem oil.
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