Cannabis Pest Identification: Photos and Fixes for Every Bug

Bottom line: Identify the pest first. Then treat with the right product. Wrong treatments waste time and money. Most indoor pests come from contaminated soil, clones, or clothing. Catch them in the first 3 days before populations multiply.

Pests kill cannabis plants fast. Spider mites double their population every 3–5 days. Fungus gnats destroy root systems in 1–2 weeks. Aphids can cover a plant in 48 hours under the right conditions.

This guide shows you what each pest looks like, what damage it causes, and exactly how to kill it.

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How to Inspect Your Plants

Do a full inspection every 3–4 days. Catch problems early.

What to look at:

• Undersides of leaves — Most pests hide here
• Soil surface — Fungus gnats, root aphids
• Growing tips — Aphids, thrips, broad mites
• Stems and nodes — Aphids, scale insects
• Roots (for hydro or fabric pots) — Root aphids, pythium

Use a jeweler’s loupe or clip-on phone microscope (30–60x magnification). You can’t identify spider mites or broad mites with the naked eye. A $10 loupe from Amazon changes everything.

Yellow sticky traps catch flying pests and tell you what’s in your space. Hang one per 4×4 tent section. Check weekly.

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Pest 1: Spider Mites

The most feared cannabis pest. Can destroy a crop in 2 weeks.

What They Look Like

Spider mites are tiny — 0.5mm long. You need a loupe to see individual mites. They are oval-shaped and range from yellow to green to red.

What you’ll see first:

• Tiny yellow or white speckles on the tops of leaves (stippling)
• Fine webbing under leaves and between branches
• Leaves that look dusty or bronzed from a distance

Under a loupe: small moving dots on the underside of leaves. Eggs look like tiny round spheres stuck to leaf hairs.

Damage Pattern

Stippling starts as tiny dots and expands. Heavily infested leaves turn yellow, bronze, then die. In severe infestations, plants get covered in white webbing.

How They Get In

• On your clothing from outside
• On clones
• Through open windows
• On tools from other grows

Treatment

Mild infestation (stippling, no webbing):

1. Spray plants with Spinosad (Captain Jack’s Deadbug) — covers all leaf surfaces including undersides
2. Spray again in 3 days
3. Spray again in 7 days (kills newly hatched eggs)
4. Wipe down tent walls with isopropyl alcohol

Moderate infestation (some webbing):

1. Start with a strong blast of cold water to knock mites off
2. Apply Spinosad same day
3. Switch to Neem oil spray on day 3 (rotating products prevents resistance)
4. Spray Spinosad again on day 7
5. Continue rotating every 3–4 days

Severe infestation (heavy webbing, dying leaves):

• Consider Avid (abamectin) for very heavy populations — use before flower only
• Remove most heavily infested leaves and bag them immediately
• Treat every 3 days for 3 weeks minimum

Never use Avid in flower. It’s a systemic pesticide that doesn’t wash off.

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Pest 2: Fungus Gnats

The most common indoor cannabis pest. They look harmless but destroy roots.

What They Look Like

Adult fungus gnats are small black flies — about 2–3mm long. They look like tiny fruit flies with longer legs. They fly slowly and hover near the soil.

Larvae are white, clear, or translucent worms with a black head. Up to 5mm long. They live in the top 2–3 inches of soil.

Damage Pattern

Adults don’t damage plants. Larvae eat organic matter in soil and attack plant roots.

Signs of root damage:

• Stunted growth
• Yellowing lower leaves
• Wilting even when watered
• Visible larvae when you dig into top inch of soil

Heavy infestations kill young plants within 2 weeks.

How They Get In

• Contaminated soil or compost
• Open doors and windows
• Overly wet soil is the main cause

Treatment

Step 1: Let the soil dry out. Fungus gnat larvae need moisture to survive. Let the top 2–3 inches of soil dry completely between waterings. This alone stops mild infestations.

Step 2: Sticky traps. Place yellow sticky traps flat on the soil surface. They catch adult gnats before they lay more eggs.

Step 3: Bacillus thuringiensis var. israelensis (Bti). This is a bacteria that kills larvae in the soil. Products: Gnatrol, Mosquito Dunks (crushed and dissolved in water). Water into the soil. Safe for plants, safe for humans. Most effective treatment.

Step 4: Diatomaceous Earth (DE). Sprinkle a thin layer on the soil surface. Sharp particles kill larvae that move through it. Reapply after watering.

Step 5: Neem oil soil drench. Mix 1 tablespoon neem oil + 1 teaspoon dish soap per gallon of water. Water into soil every 5–7 days.

Combine all 4 steps for fast results.

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Pest 3: Aphids

Fast breeders. Can cover a plant in 48 hours.

What They Look Like

Aphids are 1–3mm long. They come in many colors: green, yellow, black, white, or brown depending on species. They have pear-shaped bodies and two tubes (cornicles) on their rear end.

Found in clusters — mostly at growing tips, under leaves, and on stems.

Damage Pattern

Aphids pierce the plant and suck sap. This causes:

• Curled or cupped leaves at growing tips
• Yellow spots on leaves
• Sticky residue (honeydew) on leaves and stems
• Black sooty mold growing on the honeydew
• Ants on the plant (they farm aphids for honeydew)

Treatment

Blast with water first. A strong spray of water knocks 60–80% of aphids off the plant. Do this before applying anything.

Insecticidal soap spray: Mix 2 tablespoons of pure castile soap (Dr. Bronner’s) per quart of water. Spray all leaf surfaces including undersides. Contact kill — must hit the aphids directly.

Neem oil: Mix 1 tablespoon neem per quart of water + 0.5 teaspoon soap as emulsifier. Spray every 3–4 days.

Spinosad: Effective on aphids. Use if soap/neem doesn’t clear the infestation in 7 days.

Pyrethrin spray: Fast knockdown. Use as a reset when populations are very high.

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Pest 4: Thrips

Hard to see, but leave very distinctive silvery damage.

What They Look Like

Thrips are 1–2mm long. They look like tiny slivers — narrow, elongated, light yellow to brown. They move fast when disturbed.

Larvae are lighter in color and don’t have wings.

Look for thrips at growing tips and on the undersides of young leaves.

Damage Pattern

Thrips scrape the surface of leaves and eat the cell contents. This leaves:

• Silver or bronze streaks on leaves
• Small black dots (thrip droppings) near the streaks
• Distorted or curled new growth in heavy infestations

Thrips can also spread plant viruses.

Treatment

• Spinosad spray — most effective treatment for thrips. Apply every 3 days for 2 weeks.
• Insecticidal soap — kills on contact. Spray thoroughly on growing tips and leaf undersides.
• Blue sticky traps — thrips are attracted to blue more than yellow. Place near the canopy.
• Predatory insects — Amblyseius cucumeris is a predatory mite that eats thrip larvae. Good for preventative use or early infestations.

Thrips pupate in the soil. Treat soil with DE or Bti while treating foliage.

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Pest 5: Whiteflies

Clouds of tiny white flies that erupt when you brush the plant.

What They Look Like

Whiteflies are 1–2mm long with white powdery wings. When you shake an infested plant, hundreds of tiny white flies erupt in a cloud.

Eggs and nymphs are on the undersides of leaves. Eggs are white, oval, and arranged in semicircles.

Damage Pattern

Whiteflies suck sap from leaves. This causes:

• Yellow leaves
• Sticky honeydew on leaves
• Sooty mold on honeydew
• Leaf drop in heavy infestations

Treatment

• Insecticidal soap or pyrethrin spray — contact kill of adults
• Neem oil — disrupts the life cycle of nymphs and eggs
• Yellow sticky traps — catch adults, reduce population pressure
• Spinosad — effective, but rotate with other products

Whiteflies develop resistance fast. Rotate between at least 3 products on a 3-day schedule.

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Pest 6: Broad Mites

Invisible to the naked eye and easy to mistake for a nutrient deficiency.

What They Look Like

Broad mites are 0.2mm. You cannot see them without a 60–80x loupe. They are pale yellow to white and very fast-moving.

You identify broad mites mostly by the damage they cause, not by seeing them.

Damage Pattern

Broad mites inject a toxic chemical into the plant as they feed. This chemical is a growth regulator. It causes:

• New growth that looks twisted, curled, or blistered
• Leaves that look shiny or wet but aren’t
• Very slow or distorted new growth
• Growing tips that look stunted and deformed

This damage looks a lot like nutrient burn, pH problems, or virus. Use a loupe and look at the newest growth to confirm.

Broad mites cluster on the newest growth — growing tips, young leaves, and calyx areas in flower.

Treatment

Broad mites are harder to kill than spider mites because they hide deep in buds and growing tips.

• Spinosad — most effective, apply every 2 days
• Neem oil — use as a second product, rotating with Spinosad
• Heat treatment — place infected plants in a room at 115°F for 30 minutes. This kills broad mites (and their eggs) without hurting the plant. Hard to do precisely but very effective.
• Predatory mites — Neoseiulus californicus eats broad mites.

Act fast. Broad mites spread between plants by contact.

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Pest 7: Root Aphids

Underground and slow to notice. Often fatal by the time you find them.

What They Look Like

Root aphids look similar to foliar aphids: 1–2mm, oval, waxy coating. They live on the roots and at the base of the plant underground.

You find them when:

• You pull a plant from its pot
• You notice white waxy residue at the soil surface
• You see ants farming the soil surface

Winged adults can appear in the soil or near the base of the plant. They look like tiny winged aphids.

Damage Pattern

Root aphids suck sap from the root system. Plants show:

• General decline with no obvious cause
• Yellowing leaves that don’t respond to feeding
• Stunted growth
• Wilting that doesn’t recover after watering

By the time above-ground symptoms appear, the infestation is usually severe.

Treatment

Root aphids are very difficult to eliminate:

• Spinosad soil drench — water with Spinosad solution every 5 days
• Neem oil soil drench — water with neem/soap mix every 5–7 days
• Beneficial nematodes (Steinernema feltiae) — microscopic worms that attack root insects. Highly effective. Water into soil.
• Pyrethrin drench — strong knockdown, but works on contact only

Root aphids often require 4–6 weeks of treatment. Consider whether the plant is worth saving based on how far into its life cycle it is.

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Pest 8: Caterpillars and Budworms

Mostly an outdoor problem, but they get into greenhouses and open grows.

What They Look Like

Caterpillars range from 5–40mm depending on species. Green, brown, or striped. They have legs and move slowly.

Budworms are small caterpillars (10–20mm) that tunnel directly into buds.

Damage Pattern

• Holes chewed in leaves
• Buds with dark green or black droppings (frass) on or near them
• Hollowed-out bud sites
• Bud rot spreading from the inside out (caterpillar damage creates an entry point for botrytis)

Check for budworms by gently opening buds and looking inside. Budworms are well-camouflaged.

Treatment

• Spinosad spray — most effective organic option for caterpillars. Targets lepidoptera specifically.
• BT spray (Bacillus thuringiensis var. kurstaki) — targets caterpillars only. Apply to buds and leaves. Safe to use in flower.
• Hand-pick caterpillars when visible.

Treat every 5–7 days. Caterpillar eggs hatch in waves.

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Pest 9: Scale Insects

Looks like tiny brown bumps on stems. Easy to miss.

What They Look Like

Scale insects look like small bumps or shells stuck to stems and branches. 1–5mm. Brown, tan, or white. They don’t move once settled.

They attach to stems, branches, and sometimes the undersides of leaves.

Damage Pattern

• Small bumps on stems that don’t come off easily
• Yellowing leaves
• Honeydew and sooty mold
• Weak, struggling plants despite good care

Treatment

• Scrape scale off with a soft toothbrush dipped in isopropyl alcohol
• Spray with neem oil or insecticidal soap
• Repeat weekly for 4–6 weeks
• Scale are protected by their shell, so contact sprays work best when applied to the crawler stage (young, mobile scale before they form their shell)

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Pest 10: Russet (Hemp) Mites

Similar to broad mites in damage but different species.

What They Look Like

Russet mites are 0.1–0.2mm. Completely invisible without a 60–80x loupe. Shaped like a carrot — narrow at the rear.

They tend to climb upward on the plant, feeding as they go. Early infestations start at the base of the plant.

Damage Pattern

Different from broad mites. Russet mites cause:

• Leaves that curl up at the edges (taco shape)
• Leaves that look dry, brown, or bleached
• A “burned” look starting at the bottom of the plant and moving up

Treatment

Same as broad mites:

• Spinosad spray every 2 days
• Neem oil alternating with Spinosad
• Predatory mites (Neoseiulus californicus)
• Act fast — they spread rapidly

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Integrated Pest Management (IPM): Prevention First

The best pest control is prevention.

Preventative measures:

1. Change clothes before entering the grow. Mites and thrips ride in on fabric.
2. Quarantine new clones or plants for 2 weeks before adding to your grow.
3. Start with sterile soil. Don’t use outdoor soil or unsterilized compost.
4. Keep humidity in check. Below 60% in veg, 40–50% in flower.
5. Use HEPA filtration on intake air if possible.
6. Clean the tent with bleach or hydrogen peroxide between grows.
7. Run a preventative Neem oil drench on soil before planting.
8. Use yellow and blue sticky traps from day 1. They give early warning.

Preventative spray schedule (once per week in veg):

• Week 1: Neem oil foliar spray
• Week 2: Spinosad foliar spray
• Week 3: Insecticidal soap foliar spray
• Repeat cycle

Stop all foliar sprays 2–3 weeks before harvest.

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Quick Reference: Pest vs. Damage

Pest	Where to Look	Key Damage Sign
Spider mites	Leaf undersides	White stippling + webbing
Fungus gnats	Soil surface	Larvae in soil, stunted growth
Aphids	Growing tips, stems	Clusters, honeydew, curled tips
Thrips	Young leaves, tips	Silver streaks + black dots
Whiteflies	Leaf undersides	White cloud when plant is shaken
Broad mites	Newest growth	Twisted, blistered new leaves
Root aphids	Roots, soil base	Waxy residue, general decline
Caterpillars	Buds, leaves	Holes, frass in buds
Scale	Stems, branches	Brown bumps on stems
Russet mites	Base of plant upward	Taco-shaped leaves, bronze color

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Recommended Products to Keep on Hand

Product	Pests It Targets
Spinosad (Captain Jack’s Deadbug)	Spider mites, thrips, aphids, caterpillars, broad mites
Neem oil	Spider mites, aphids, whiteflies, fungus gnats
Insecticidal soap	Aphids, spider mites, whiteflies, thrips
Gnatrol / Mosquito Dunks	Fungus gnats (larvae), caterpillars
Diatomaceous Earth	Fungus gnats, crawling insects
Pyrethrin spray	Fast knockdown on most soft-bodied insects
Beneficial nematodes (Sf)	Root aphids, fungus gnat larvae

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Final Word

Pests move fast. A spider mite population goes from 20 to 2,000 in 10 days. Fungus gnats turn a healthy root zone into rotted mush in 2 weeks.

Inspect every 3–4 days. Use a loupe. Hang sticky traps.

When you find something, identify it first. Then treat with the right product. Rotating treatments prevents resistance.

Prevention is worth 10 treatments. Clean tent, quarantine clones, control humidity. Start there.