Spider Mites and Common Cannabis Pests

Why pests still hit indoor grows

A tent is not a sealed biosphere. Mites ride in on clothes, clones, pets, or new plants. Fungus gnats breed in wet soil. Thrips sneak through intake vents. The enclosed space that protects your crop also concentrates an infestation once it starts.

Prevention beats cure — but every long-term grower deals with pests eventually. Early detection is the difference between a wiped leaf and a lost harvest.

Spider mites

The #1 indoor cannabis pest. Microscopic sap-suckers that reproduce explosively in warm, dry tent conditions.

• Fine webbing on bud sites and leaf undersides (late stage)
• Tiny yellow or white speckles on top of leaves — stippling
• Leaves look dull or bronzed; overall vigor drops
• Shake a leaf over white paper — red/brown moving specks confirm mites

Fungus gnats

Small black flies around soil — larvae eat fine root hairs in wet medium. Often a sign of overwatering, not a random invasion.

• Adults fly up when you water or bump the pot
• Sluggish growth, especially seedlings and clones
• Sticky traps catch adults; let soil dry between waterings
• Yellow sticky cards near soil surface monitor population

Thrips, aphids, and broad mites

Less common but worth knowing the signatures:

• Thrips: silver streaks on leaves, black specks (frass), fast-moving slender insects
• Aphids: clusters on stems and new growth, sticky honeydew, ants sometimes present
• Broad/russet mites: harder to see — distorted new growth, rough leaves, no obvious webbing

Prevention checklist

Build these habits before you need them:

• Quarantine new clones or mother plants for 7–14 days
• Inspect undersides of leaves weekly with a loupe
• Keep humidity in check — mites thrive in hot, dry late flower
• Remove dead leaf litter from tent floor
• Don't bring outdoor clothes/tools into the tent unwashed
• Sticky traps in corners — early warning, not a full treatment

Treatment approach

In flower, avoid harsh systemic pesticides you wouldn't want to smoke. Many growers use horticultural oils, insecticidal soaps, or predatory mites (Phytoseiulus persimilis for spider mites) — follow product labels and apply when lights are off to avoid burn.

Severe late-flower infestations are a judgment call: partial harvest, bud wash at chop, or loss. Catching mites at week 2 of flower is manageable; webbing at week 7 is a crisis.

Always treat the whole tent and adjacent plants — spot-treating one cola doesn't work.