Spider mites on weed show up first as tiny pale or yellow specks on the tops of fan leaves. Check the undersides for mites, their round eggs or fine webbing. To get rid of them, use an OMRI-listed spray or insecticidal soap on the leaf undersides every 3-5 days for at least two weeks. Once buds form, predatory mites are the safer option.
Left unchecked, spider mites cut yield and bud quality and can even kill a cannabis plant. Most indoor infestations ride in on clones or plants from another grow, which is one reason many growers start fresh from feminized weed seeds instead. In this guide, you’ll learn:
- How to identify spider mite damage, eggs and webs.
- Spider mites vs. real spiders, deficiencies, thrips and mildew.
- Causes of a spider mite infestation.
- How to get rid of spider mites in veg and flowering.
- Prevention tips to keep them away.
What Are Spider Mites on Weed Plants?
Spider mites are tiny arachnids that feed on cannabis plants by piercing leaf cells and drawing out the contents. That feeding drains the chlorophyll your plant needs to turn light into energy. Left unchecked, this steady cell damage slows growth, cuts yield and can kill a heavily infested plant.
As arachnids (not insects), most insecticides work poorly against them. The two-spotted spider mite is the species you're most likely to encounter on cannabis. Adults measure roughly 0.02 inches (0.4 mm), small enough to look like moving specks rather than distinct bugs.
Spider mites reproduce fast in warm, dry conditions. A single female can lay up to 200 eggs in her short lifetime. Left untreated, a small population can turn into a full infestation within 2-3 weeks.
How to Identify Spider Mites on Cannabis Plants
Spider mites leave three signs on cannabis plants: stippled leaf tops, mites and eggs on the leaf undersides, then webbing. The fine pale or yellow speckling shows up first, but the mites stay hidden much longer because they feed underneath the leaf. To confirm, check a suspect leaf’s underside with a magnifying loupe (mites and eggs are hard to see with the naked eye).
What Spider Mite Damage Looks Like on Fan Leaves
Cannabis leaf showing yellow-white stippling from spider mite feeding damage
Spider mite damage starts as tiny white or yellow dots scattered across the top of a fan leaf. It gives the leaf a stippled, dusty look. The dots spread outward from the first feeding sites as the population grows. Heavily damaged leaves turn pale, bronze or yellow, then dry out and drop.
The dots are emptied cells inside the leaf, so they don't wipe off when you rub them. That quick rub test separates mite stippling from dust or powdery mildew, which sit on the surface. Before you treat for anything, flip the leaf and check the underside.
What Spider Mite Eggs Look Like
Cannabis leaf underside showing spider mite eggs.
Up close, an adult spider mite has an oval body and eight legs, and it's usually pale yellow-green or straw colored. The two-spotted spider mite gets its name from the dark blotch on each side of its body. To the naked eye, they look like tiny moving dots clustered along the veins on the underside of a leaf.
In a cool fall room, you might find orange-red mites instead. These are usually the same two-spotted species switching to a resting form, not a different pest. Tiny black dots near a colony are mite waste, another sign you've found the culprit.
For a quick check, hold a sheet of white paper under a branch and tap it sharply. Dust stays put, but spider mites start walking across the paper. A 10x hand lens is enough to see them, while a 30x to 60x loupe shows the spots and eggs clearly.
What Spider Mite Webs Look Like
Spider mite webbing coating cannabis leaves and stems.
Spider mite webs appear as fine silk strands across leaves, stems and eventually buds. They signal an infestation that's moved past the early stage. Early webbing is sparse and easy to miss unless you check for it directly. Heavy webbing coats leaf surfaces and can trap dust and debris, which raises your mold risk once buds are covered.
Visible webbing on a plant usually means the population has been established for a week or more, since fine strands take time to build up.
Spider Mites vs. Real Spiders on Weed
Spider mites are closer relatives of ticks, not spiders. Real spiders are easy to see and move quickly. Their webs are larger and more structured, usually strung across gaps between branches. Spider mite webbing looks different. It's a fine, dense silk wrapped around growing tips, leaf stems and buds, crowded with tiny moving specks.
A spider mite infestation also leaves nearby leaves stippled, while real spiders leave the foliage untouched because they don't feed on it. They hunt insects and other small pests, so a few spiders in your garden usually do more good than harm.
Weed doesn't attract spiders on its own, but lots of spiders can mean there's prey around, so check your leaves for pests anyway.
What Causes Spider Mites on Cannabis Plants?
Spider mites are caused by infested clones or plants brought into your grow, contaminated clothing, pets, soil or tools, and outdoor exposure or airflow from an already-infested space. These common entry points account for most infestations:
- New clones or plants you bring in without inspecting them first.
- Clothing, shoes or hands after contact with another grow space.
- Pets that move between outdoor areas and your grow room.
- Reused soil, containers or tools from a prior grow.
- Unfiltered air intake from outside.
Warm temperatures, low humidity and poor airflow speed up whatever population does arrive. Spider mites reproduce faster once your room climbs above 75°F (24°C), while tagnant air gives them the still conditions they need to spread across a plant.
Spider Mite Damage vs. Look-Alike Problems
The scattered discoloration of fan leaves caused by spider mite damage can look a lot like a calcium or magnesium deficiency. Thrips damage and powdery mildew cause the other common mix-ups. The table below separates all five by pattern, location and progression, so you can confirm the cause before choosing a treatment:
| Trait | Spider Mite Damage | Magnesium Deficiency | Calcium Deficiency | Thrips Damage | Powdery Mildew |
| Leaf-top pattern | Fine, evenly scattered dots | Yellowing between green veins | Brown, sharp-edged blotches | Silvery streaks with small black flecks | Gray-white powdery patches |
| Rub test | Tiny specks stay | Yellowing stays | Blotches stay | Streaks stay | Powder smudges off |
| Underside signs | Eggs, moving mites, webbing | None | None | Visible thrips, light scarring | Chalk-like powdery patches |
| Progression | Spreads fast, worsening within days | Starts on older, lower leaves | Starts on new, upper growth | Streaks widen with more fleck | Patches get bigger and merge |
| Webbing | Yes, in moderate to heavy infestations | No | No | No | No |
Magnesium and calcium deficiencies are the most common look-alikes of spider mite damage. If you’ve recently added Cal-Mag or Epsom salt to your feed and new leaves keep speckling, check for mites.
Underside signs give you the clearest answer, since only spider mites leave visible eggs and webbing on the leaf's underside. Before you reach for any treatment, turn a suspect leaf over and check with a loupe, what you find (or don't) underneath tells you more than the surface damage ever will.
If you only find specks on top and nothing underneath, check a few more leaves before you treat. Once you spot mites or eggs, start treatment right away.
How to Get Rid of Spider Mites on Cannabis Step By Step
To get rid of spider mites on cannabis, cool your grow room to slow them down, then pick one treatment (don’t combine them): botanical oil sprays and insecticidal soap kill mites on contact, so they need repeat rounds. Alternatively, use predatory mites, which eat adults and eggs. Since they don’t leave residue, they're a safe choice once buds form.
Follow the steps below in order:
Step 1: Cool the Room and Keep Air Moving
Keep temperatures below 80°F, ideally closer to 75°F, and a fan for a steady breeze across the canopy. Mites breed faster in warm, still air, and wind makes it harder for them to move around and breed. Nudging humidity up in veg and early flower slows them too. It won’t kill eggs, though, and must come back down once buds form to avoid mold.
Step 2: Remove the Worst Leaves and Knock Down Webbing
Strip any heavily damaged leaves and fallen debris, and carefully bag them for disposal before they leave the grow. On a heavily infested veg plant, use plain water to rinse off any thick webbing or vacuum it off so treatments can reach the mites underneath.
Step 3: Pick One Program: Sprays or Predatory Mites
Sprays kill beneficial mites too, so don’t alternate between them or run both at once. Choose sprays if you don’t use beneficial insects, or predatory mites for an ongoing biological program. On a heavy outbreak, you can sequence them. Finish your spray rounds first, then release predators after the final spray, once the label says it’s safe for beneficials.
Step 4: If You Spray, Choose a Botanical Oil or Insecticidal Soap
OMRI-listed sprays made from oils like rosemary, clove, cinnamon, thyme or peppermint kill spider mites on contact, and insecticidal soaps work the same way. Many are safe for use up to harvest day, but check the label before you spray flowering plants. Neem oil and azadirachtin products help in veg, but keep them off any buds since they can affect taste.
Contact sprays leave little lasting residue, so coverage is everything. Use a fine mist that reaches the undersides of leaves, where the mites live.
Step 5: Repeat Every 3-5 Days For 2 Weeks Minimum
Each spray round catches mites that hatched since the last one. Alternate two products that kill in different ways, since two-spotted spider mites build resistance quickly. Run the schedule longer in a cooler room, where mites develop more slowly.
Step 6: If You Use Predatory Mites, Match the Species to the Job
Phytoseiulus persimilis is the one for an active outbreak. It eats spider mite eggs, nymphs and adults fast, but moves on or dies off once prey runs low. Neoseiulus californicus holds up at low pest levels, ideal for prevention and background control. Slow-release sachets hung in the canopy release new hunters over several weeks.
Step 7: Treat Consistently and Check New Growth
With consistent treatment, most spider mite infestations clear within 2-4 weeks. Old stippling won’t fade, so judge progress by carefully inspecting new leaves and leaf undersides. If you still find moving mites, run the schedule again with two different products, since survivors may have built resistance to the first pair.
How to Get Rid of Spider Mites During Flowering
To get rid of spider mites during flowering, release predatory mites at the first sign of activity and keep any spray off your buds. Speed matters more now than at any other stage. Once mites web over your flowers, the silk traps debris inside the buds, raises mold risk and is almost impossible to clean out. Here are your options in flower, from first choice to harvest:
- Predatory mites. They’re your best option, since they work inside the canopy without wetting your buds. They knock back a working population but won’t rescue a plant that’s already webbed over.
- Leaf-only sprays. OMRI-listed botanical sprays or insecticidal soap can go on the leaves and outer canopy. Check the label for flowering use, and never soak the buds, since wet flowers invite mold.
- Alcohol spot treatment. Dab a diluted isopropyl alcohol mix directly on visible colonies, well away from the buds. Use it sparingly, since alcohol can burn plant tissue.
- Early harvest. If webbing reaches your buds in the final week or two, check the trichomes. When they’re close to ready, harvesting a few days early usually costs less than letting mites work through your colas.
- Bud wash at harvest. A brief hydrogen peroxide wash and clean water rinse removes leftover mites, eggs and webbing. Dry the buds thoroughly with gentle airflow before your normal dry and cure. Buds matted with webbing are hard to clean fully, so they’re safer in the trash than in your jar.
How to Prevent Spider Mites on Cannabis Plants
Preventing spider mites comes down to keeping them out and making your grow a poor place to breed. Most indoor infestations trace back to a clone or plant that carried mites or eggs in undetected, so a 2-3 week quarantine period comes first. Clean, breezy conditions and regular checks handle the rest.
Quarantine New Clones and Plants
New cannabis clones and plants carry the highest risk of introducing spider mites into your established grow. Inspect every incoming crop under a loupe and check both sides of the leaves to catch most visible eggs and mites before they spread.
Dip small plants in room-temperature water treated with a mild insecticidal soap to add another layer of protection. Keep new plants separate from your main grow for 2-3 weeks to give any missed eggs time to hatch and reveal themselves.
Keep the Grow Room Clean and Well-Ventilated
Warm, stagnant, dry air gives spider mites the conditions they need to reproduce quickly and spread between plants. Strong airflow across your canopy makes it harder for mites to settle and mate, while also helping treatments dry faster once applied.
Removing dead leaves and plant debris regularly closes off places where mites and eggs can hide between grow cycles. Changing clothes after visiting another grow space, and keeping pets out of your grow room entirely, closes two of the most common entry points. If your intake pulls air from outside, a filter on it keeps mites from riding in.
Check Leaf Undersides Every Week
Weekly scouting catches mites while they're still a few specks instead of a colony. Once a week, flip leaves from the top and middle of each plant and check the undersides with a loupe. The paper tap test works too. Keep it up from seedling to harvest, since mites multiply quickly in a warm room between checks.
Protect Outdoor Cannabis Plants
Outdoor cannabis plants get spider mites too, especially during hot, dry, dusty spells. Rain, wind and natural predators usually keep outdoor populations lower than indoor ones. Protect those predators: skip broad-spectrum insecticides, since they kill the beneficial bugs that keep spider mites in check and can trigger a flare-up.
Inspect your weed plants regularly for spider mites. Check leaf tops and undersides at least once a week through summer, especially during any heat waves.
How Starting From Seed Lowers Spider Mite Risk
Cannabis seeds arrive free of the spider mites that commonly hitchhike in on clones or weed plants from another grow.
A clone carries whatever mites or eggs were already on its mother or neighboring plants. A seed starts as a clean slate, with no leaves for mites to live on until it sprouts in your space.
That difference matters most if you've dealt with a stubborn mite population before. Starting fresh from seed removes your single biggest introduction risk. Many growers take clones to guarantee female plants, but feminized seeds grow into female plants without the pest risk a cutting can carry.
If you prefer clones, source them carefully. Clean-stock, lab-tested clones from a reputable supplier are a safer bet than cuttings from a friend's grow, but they still need checking.
Pair that with a proper quarantine and inspection before they join your main grow, and you close off most of the risk a clone would otherwise carry.
