Identifying and Preventing Colorado’s Most Common Cannabis Pests

Growing cannabis at home in Colorado is a rewarding, legal adventure - but if you’re keeping your grow indoors (as the law requires unless you meet strict private enclosure conditions), pests can still sneak in and cause serious damage. While you’re safe from deer and grasshoppers, you’re not immune to the tiny invaders that love warm, dry indoor conditions.

Below is a detailed guide to the most common indoor cannabis pests Colorado growers face - and exactly how to prevent and manage them.

1. Fungus Gnats

The tiny black flies that love your moist pots.

What to Look For:

• Tiny black flies buzzing around soil or pots
• Larvae (clear, worm-like with black heads) wiggling just below the surface
• Yellowing leaves and signs of overwatering

Why They’re a Problem:

Their larvae chew on delicate roots, stressing your plants and inviting disease.

How to Prevent & Eliminate:

• Let the top inch of soil dry before watering
• Use sticky traps to catch flying adults
• Apply BTi (Bacillus thuringiensis israelensis) to the soil as a safe, effective larvicide
• Add a top layer of perlite or sand to dry out the soil surface

2. Spider Mites

Colorado’s #1 indoor enemy - and they’re nearly invisible.

What to Look For:

• Tiny yellow or white specks (stippling) on leaves
• Very fine webbing under leaves or at branch junctions
• Mites visible with a loupe - usually red, brown, or tan

Why They’re a Problem:

They multiply rapidly and thrive in dry environments - aka, a typical Colorado home in winter.

How to Prevent & Eliminate:

• Keep indoor humidity at 50–60% to make your space less inviting
• Wipe or spray leaves with neem oil or insecticidal soap
• Introduce predatory mites (Phytoseiulus persimilis) in sealed tents or grow rooms
• Quarantine new clones or plants before introducing them

3. Aphids

Soft-bodied suckers that multiply like crazy in small spaces.

What to Look For:

• Clusters of tiny green, black, or white bugs on stems and leaf undersides
• Sticky residue on leaves (called honeydew)
• Curling or distorted new growth

Why They’re a Problem:

They feed on plant sap, stunt growth, and can spread viruses or lead to mold.

How to Prevent & Eliminate:

• Spray plants with water to knock aphids off
• Use neem oil or insecticidal soap
• Introduce ladybugs (if your space allows) or keep your environment pest-free with regular monitoring
• Seal your grow room and inspect vents or ducting for entry points

4. Thrips

Tiny slashers that leave silver trails on your leaves.

What to Look For:

• Silvery streaks or scarring on leaf surfaces
• Fast-moving, needle-like bugs (often white or tan)
• Black specs (thrip poop) left behind

Why They’re a Problem:

Thrips puncture cells to feed, which disrupts photosynthesis and stresses your plant.

How to Prevent & Eliminate:

• Hang blue sticky traps (they’re attracted to blue light)
• Use Spinosad-based sprays, safe for indoor cannabis
• Wipe leaves and clean surfaces regularly
• Consider Orius insidiosus, a tiny predatory bug for enclosed tent environments

5. Whiteflies

More annoying than damaging, but still not welcome.

What to Look For:

• Tiny white bugs fluttering when you disturb the plant
• Eggs laid in spirals on leaf undersides
• Sticky leaves and mild leaf yellowing

Why They’re a Problem:

They reduce vigor and can trigger mold problems in a tightly controlled indoor environment.

How to Prevent & Eliminate:

• Set yellow sticky traps
• Spray with insecticidal soap or neem oil
• Install a bug screen over air intakes
• Clean your tent or grow area thoroughly between grows

Indoor Grower Pest Prevention Tips (Colorado-Specific)

• Seal your space: Bugs get in through vents, ductwork, windows, and clothing
• Monitor humidity carefully: Too dry = spider mites. Too moist = fungus gnats
• Clean your grow area weekly: Wipe down surfaces, remove old leaves, and vacuum floors
• Inspect plants daily: Early detection makes all the difference
• Avoid bringing outdoor plants or soil inside unless sterilized
• Quarantine all new clones or seeds that have sprouted elsewhere

Keep It Clean, Keep It Controlled

Colorado home cannabis grows must be indoors by law - and that’s a win when it comes to controlling the environment. But pests don’t care about rules. Stay alert, stay clean, and rotate your pest control methods to keep resistance down. With a sealed, well-managed space, your cannabis plants can thrive pest-free all the way to harvest.

From elevation-specific growing advice to organic pest control ideas, HomeGrow Helpline's mission is simple: Make home growing easier, smarter, and a whole lot more fun.