# Spider mites on cannabis: ID, lifecycle and IPM

> Twospotted spider mites (Tetranychus urticae) cause pale stippling on leaf tops and webbing at heavy populations; they breed fastest in hot, dry rooms, so control rests on early scouting, cooler and more humid conditions, and predatory mites released before numbers explode, with soaps or oils only before flower.

- Canonical: https://genetixbay.com/knowledge/pests/spider-mites.html
- Category: Pests · Level: Beginner
- Evidence: Established · Status: Draft: awaiting expert review (some figures are being checked)
- Stage: Veg, Transition, Flower · Systems: Any system
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Questions and answers

**What are the tiny dots on my cannabis leaves?** Tiny pale dots on the upper surface of cannabis leaves are usually stippling from twospotted spider mites (Tetranychus urticae), each dot an emptied leaf cell. Turn the leaf over: a 10 to 20x lens shows oval mites about 0.5 mm with two dark blotches, plus round clear eggs. No mites and no eggs means it is not mites; consider thrips or nutrient spotting.

**How do I get rid of spider mites in flower?** In flower, spider mites are controlled with predatory mites, removal of infested leaves and accepting some damage, not sprays. Soaps, oils and sulfur leave residues on buds and wet buds invite [botrytis](https://genetixbay.com/knowledge/glossary/botrytis.md), and most systemic miticides are not registered on cannabis. Do not raise humidity in late flower to slow mites. If a late-flower infestation is severe, harvest early rather than spray.

**Which predatory mite should I use for spider mites?** For spider mites, Phytoseiulus persimilis is the specialist choice for established hot spots, eating 5 to 20 prey a day, but it needs about 70% RH and fails above about 32 °C (90 °F). Neoseiulus californicus tolerates warmer, drier rooms and survives on few prey, so it suits preventive release. Release early, when mites are first seen, and avoid residual pesticides.

**Is there webbing on my buds from spider mites?** Silk webbing over cannabis buds and leaf tips, with mites massing at the top of the web, is a sign of a heavy twospotted spider mite population. By the time webbing appears, numbers are already large. Confirm with a 10 to 20x lens or by tapping a branch over white paper and watching for moving specks that streak when smeared.

**How fast do spider mites reproduce?** Spider mites reproduce fastest in heat: egg-to-adult takes roughly 5 days at 24 °C (75 °F) versus about 40 days at 13 °C (55 °F), according to a general extension source rather than cannabis data. University research notes a generation can finish in under a week with favourable temperature and food. Hot rooms above 28 °C (82 °F) and below 40% RH favour them.

**Short answer.** Fine pale speckles on the upper leaf surface, tiny moving dots underneath, and later silk webbing: that is almost always the twospotted spider mite. A generation can finish in under a week when it is warm, so find them early, cool the room and raise humidity where you can, and release predatory mites while numbers are still low. Contact sprays belong in veg, not on flowers.

## What's happening

Spider mites (Tetranychus urticae, the twospotted spider mite, is the usual one indoors) pierce leaf cells and suck out the contents. Each emptied cell shows as a pale dot (stippling). Enough dots and the leaf bronzes, yellows and dies; [photosynthesis](https://genetixbay.com/knowledge/glossary/photosynthesis.md) and yield fall with it [1][3].

**Lifecycle.** Egg, larva, two nymphal stages, adult [1]. Speed depends on temperature: roughly 40 days egg-to-adult at 13 °C (55 °F) versus about 5 days at 24 °C (75 °F) [6]. UC [IPM](https://genetixbay.com/knowledge/glossary/ipm.md) states a generation can finish in under a week under favourable temperature and food [1]. Hot, dry, dusty conditions favour them [1][3].

## How to recognise it

- **Leaf tops:** fine white-yellow stippling, starting on scattered leaves, often mid-canopy or near hot spots.
- **Leaf undersides:** a hand lens (10–20x) shows oval mites about 0.5 mm, pale yellow-green with two dark blotches, plus round clear eggs and cast skins [1][4].
- **Shake test:** tap a branch over white paper; moving specks that streak when smeared are mites [3].
- **Heavy populations:** silk webbing at leaf tips and over colas, a "dirty" look, mites massing at the top of the web [3].

Do not confuse with: broad/[russet mites](https://genetixbay.com/knowledge/glossary/hemp-russet-mite.md) (no stippling-and-web pattern, twisted or bronzed growth, mites invisible at 10x), thrips (silvery scars and black fecal specks), or nutrient spotting (no mites, no eggs). See [kb-diagnosis-rust-spots](https://genetixbay.com/knowledge/diagnosis/rust-spots.md).

## Numbers that matter

| Parameter | Value | Notes |
|---|---|---|
| Adult size | ~0.5 mm | Visible as a dot; 10–20x lens to confirm [1] |
| Egg-to-adult | ~5 days at 24 °C (75 °F); ~40 days at 13 °C (55 °F) | |
| Development threshold | ~11 °C (52 °F) | Pacific spider mite model; T. urticae similar |
| Phytoseiulus persimilis RH need | ≥ ~60–70% RH | Immature predators fail to moult below ~70% RH [2] |
| P. persimilis heat limit | releases failed above ~32 °C (90 °F) | Greenhouse poplar trial (non-cannabis) |
| Predator feeding | 5–20 prey/day (adult P. persimilis) | [2] |
| [Action threshold](https://genetixbay.com/knowledge/glossary/action-threshold.md) | none established for cannabis | Grower practice: act on first confirmed colonies |

## What to check first

1. **Confirm the pest.** Lens on leaf undersides; shake test. No mites, no eggs = not mites.
2. **Map the spread.** Flag every infested plant. Hot spots near lamps, walls and fans are typical.
3. **Read the room.** [Leaf temperature](https://genetixbay.com/knowledge/glossary/leaf-temperature.md), RH and [VPD](https://genetixbay.com/knowledge/glossary/vpd.md). Hot (>28 °C / 82 °F) and dry (<40% RH) rooms favour mites.
4. **Find the source.** New clones, a nearby houseplant, a pet, your clothes after the garden.
5. **Check plant stress.** Drought-stressed and dusty plants suffer more [3].

## How to fix it

Registrations for pesticides on cannabis differ by country, state and province, and many products are not legal on cannabis at all. Always check local regulations and follow the label. This article names classes, not products or rates.

### Cultural
- Quarantine new plants 1–2 weeks and inspect them before they enter the room.
- Avoid drought stress; keep foliage free of dust [3].
- Where the stage allows, keep temperatures moderate and RH toward the upper end of the safe range for the stage (in veg, 60–70% RH is often workable). Do not raise RH in late flower; bud rot costs more than mites ([kb-diseases-botrytis-bud-rot](https://genetixbay.com/knowledge/diseases/botrytis-bud-rot.md)).
- Remove and bag heavily infested leaves or whole plants; do not shake them through the room.

### Physical
- A strong water spray on leaf undersides knocks down mites in veg (Grower practice).
- Wash hands and change clothes before moving between rooms; work clean rooms first.
- [Sticky cards](https://genetixbay.com/knowledge/glossary/sticky-trap.md) do not catch spider mites usefully; use a lens.

### Biological
- **Phytoseiulus persimilis:** specialist; eats all mobile stages, 5–20 prey per day [2]. Needs RH around 70% and dies or starves above ~32 °C or when prey run out, so it often needs repeat releases [2][5]. Best on established hot spots.
- **Neoseiulus californicus:** generalist; tolerates warmer, drier conditions and survives on low prey numbers, so it suits preventive use (Supported).
- **Other options:** Feltiella acarisuga (predatory midge) and Stethorus punctillum (mite-eating [lady beetle](https://genetixbay.com/knowledge/glossary/ladybird.md)) are sold for hot spots.
- Release early, when mites are first seen [4]. Confirm rates with the supplier. Avoid residual pesticides before and after release.

### Least-toxic options
- **[Insecticidal soaps](https://genetixbay.com/knowledge/glossary/insecticidal-soap.md) (potassium salts of fatty acids):** contact only; must hit the mites on leaf undersides; repeat needed because eggs survive [3].
- **Horticultural oils:** smother eggs and mites; avoid in heat, under lights, and on stressed plants.
- **Entomopathogenic fungi** (e.g. Isaria fumosorosea): listed in hemp extension notes [3]; need humidity to work.
- **Sulfur:** has miticidal activity, but it harms predatory mites and can burn foliage if mixed with or applied near oils. Keep it out of programmes that rely on beneficials.

### What not to do in flower
- Do not spray soaps, oils or sulfur onto developing buds; residues end up in the product, and wet buds invite botrytis.
- Do not use systemic or residual miticides; most are not registered for cannabis and residues fail [compliance testing](https://genetixbay.com/knowledge/glossary/compliance-testing.md) in regulated markets.
- Do not jack RH in late flower to slow mites.
- In flower, rely on predators, removal of infested leaves, and accepting some damage; if the infestation is severe in late flower, harvest early rather than spray.

## How to confirm it worked

- Re-check flagged plants with a lens every 3–4 days: fewer live mites and eggs, predators present (P. persimilis is bright orange-red, faster, no dark blotches [2]).
- New leaves emerge without stippling. Old stippling does not heal; judge by new growth.
- Two clean checks a week apart before you relax.

## Common mistakes

- Waiting for webbing. By then the population is large.
- Treating only the visible plants. Mites walk and ride air currents.
- Releasing P. persimilis into a hot, [dry room](https://genetixbay.com/knowledge/glossary/drying-room.md) and wondering where they went.
- Rotating through sprays with no change to climate or hygiene.
- Mistaking broad or russet mite damage for spider mites and treating the wrong pest.

## Evidence

- Lifecycle, damage and stippling/webbing signs: *Established* [1][3].
- Temperature dependence of development: *Established* in general entomology; the exact day counts here are from a non-cannabis extension source [6].
- Phytoseiulus persimilis as a top biocontrol agent and its humidity needs: *Established* in greenhouse crops [2][5]; cannabis-specific trials are few, so this is extrapolated (*Supported*).
- Cannabis action thresholds: none published; first-sighting action is *Grower practice*.

## Sources

1. UC IPM. Pest Notes: Spider Mites (Publication 7405). University of California ANR. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html
2. UC IPM. Natural Enemies Gallery: Phytoseiulus predatory mites. https://ipm.ucanr.edu/natural-enemies/phytoseiulus-predatory-mites/
3. Utah State University Extension. Two-Spotted Spider Mite (hemp). https://extension.usu.edu/planthealth/ipm/notes_ag/hemp-spider-mites.php
4. UConn IPM. Biological control of spider mites (2019 fact sheet). https://ipm.cahnr.uconn.edu/wp-content/uploads/sites/3216/2022/12/2019biologicalcontrolofspidermitesfinal2-1.pdf
5. University of Florida. Twospotted spider mite (bulletin). https://mrec.ifas.ufl.edu/lso/SpMite/b853a1.htm
6. University of Illinois. Home, Yard & Garden Pest newsletter: spider mites (1998). https://hyg.ipm.illinois.edu/pastpest/199807d.html