Spider mites — identification and control

How to identify spider mites

Look for these symptoms on susceptible plants:

• Fine yellow or bronze stippling on upper leaf surfaces
• Silvery, sand-blasted look to mature leaves
• Fine silk webbing on leaf undersides and between stems
• Premature leaf drop in heavy infestations
• Tiny moving dots when leaves are tapped over white paper

A spider mite egg-to-adult cycle can run as short as 7 days at 27 degC. Populations double every 2-3 days in hot, dry weather, which is why outbreaks seem to appear overnight.

Crops affected by spider mites

Spider mites are documented on the following host crops in authoritative extension sources. Click any crop for the full per-crop protocol, including symptoms specific to that host and the recommended biological control.

• Spider mites on tomatoeshigh

  Two-spotted spider mite (Tetranychus urticae) on tomato lower leaves first — yellow speckling, bronze sand-blasted look, fine webbing in leaf axils and between fruit clusters.

  Severity: High — act quickly · From mid-summer onwards during hot dry weather (above 27 degC). Inspect lower leaves weekly; mite damage moves up the plant fast once it starts.

• Spider mites on cucumbershigh

  Fine yellow stippling on cucumber leaves followed by silvering, leaf curl, and webbing under the leaves. Damaged leaves drop; fruit yield collapses in untreated greenhouse cucumbers.

  Severity: High — act quickly · From the first vining stage onwards under glass; outdoor cucumbers are at risk through mid- to late summer. Check weekly with a hand lens.

• Spider mites on beansmoderate

  Yellow stippling on bean leaves, particularly during dry spells; leaves turn bronze and drop early. Pods can be scarred if mites reach the pod surface.

  Severity: Moderate — monitor closely · Hot dry stretches in midsummer — beans next to dusty paths or south-facing walls are most exposed. Inspect under leaves weekly.

• Spider mites on rosesmoderate

  Pale stippling and faded look on rose leaves; webbing in dense leaf axils. Most common on roses against warm walls or under glass.

  Severity: Moderate — monitor closely · Late spring and through summer in warm sheltered positions. Indoor or conservatory roses are at risk year-round.

• Spider mites on strawberrieshigh

  Two-spotted spider mite on the underside of strawberry leaves — silvery bronzing, reduced fruit set, leaf cupping. Heavy infestations stunt plants and shorten the season.

  Severity: High — act quickly · From flowering onwards, especially in warm dry summers. Use a hand lens on the underside of mid-canopy leaves.

Non-chemical controls

Start with the lowest-impact options before any spray. These work for the vast majority of home garden cases.

• Raise humidity (mist foliage, group plants, run a humidifier indoors)
• Strong water spray underneath every leaf — repeat every 3-4 days
• Keep plants well watered; drought stress amplifies damage
• Quarantine and isolate infested plants before treating
• Prune out and bin heavily webbed leaves

Biological controls

For greenhouse, polytunnel, and indoor production, biological controls give long-term suppression without the residue or pollinator harm of synthetic sprays.

• Phytoseiulus persimilis — specialist predatory mite, gold standard for two-spotted spider mite (62-80 degF, 50-70 percent RH)
• Neoseiulus californicus — tolerates drier conditions than P. persimilis
• Amblyseius andersoni — general predatory mite useful for early-season releases
• Stethorus punctillum — small ladybird that feeds exclusively on mites

Organic and chemical spray options

Horticultural oil and insecticidal soap target mite eggs and adults — apply in cool morning hours, never above 30 degC or on drought-stressed plants. Avoid broad-spectrum pyrethroids, which wipe out the predators that would otherwise crash the population. Sulfur dust is approved on some crops but phytotoxic to cucurbits.

How to build a spider mites control protocol

1. Identify first. Snap a photo and confirm the species before treating — different pests respond to different protocols, and one wrong call wastes weeks. Open Growli for instant species ID.
2. Start with non-chemical control. Water blast, sticky traps, manual removal, reflective mulch, or quarantine — these alone clear roughly 60-70 percent of home cases.
3. Add biological control if you have a long-cycle crop. Greenhouse tomatoes, cucumbers, peppers, and indoor citrus all justify a single release of the right predator or parasitoid.
4. Layer in insecticidal soap or horticultural oil. Apply to thorough wetness on both leaf surfaces; repeat every 5-7 days for three weeks to catch successive hatches.
5. Reserve stronger sprays for outbreaks. Spinosad, pyrethrin, and species-specific options like Bti should be your second-line response, not your first.
6. Monitor weekly. Spider mites populations rebound from any single intervention. Two or three weeks of follow-up checks separate a fixed problem from a recurrence.

Common mistakes

• One-and-done spraying. Spider mites go through staggered hatches; a single spray misses everything that hatches afterwards. Always plan a 3-week protocol.
• Treating without confirming species. Insecticidal soap clears aphids but is wasted on slugs; Bti clears fungus gnat larvae but does nothing for spider mites. Wrong protocol equals wasted weeks.
• Spraying in hot sun. Soap and oil sprays burn leaves above 30 degC and on drought-stressed plants. Apply at dawn or dusk.
• Mixing biological control with broad-spectrum sprays. Pyrethroids and neonicotinoids wipe out predator releases. Use one strategy at a time, or stagger them by at least a week.

Frequently asked questions

How do I get rid of spider mites?

Spider mites are microscopic 0.5 mm arachnids that thrive in hot, dry, dusty conditions. They stipple leaves with tiny yellow flecks and spin fine webbing once populations build. Raise humidity, hose foliage hard, and apply insecticidal soap or horticultural oil weekly. Release Phytoseiulus persimilis predatory mites for severe greenhouse outbreaks.

What does spider mites damage look like?

Look for: Fine yellow or bronze stippling on upper leaf surfaces; Silvery, sand-blasted look to mature leaves; Fine silk webbing on leaf undersides and between stems; Premature leaf drop in heavy infestations. Each host crop shows slightly different symptoms — see the per-crop pages linked above for details.

What is the best biological control for spider mites?

Phytoseiulus persimilis — specialist predatory mite, gold standard for two-spotted spider mite (62-80 degF, 50-70 percent RH). Several other biocontrols are documented for specific conditions and host crops; see the full list above.

When during the season do spider mites appear?

Mid-summer outdoors during hot dry stretches; any time indoors with low humidity. A spider mite egg-to-adult cycle can run as short as 7 days at 27 degC. Populations double every 2-3 days in hot, dry weather, which is why outbreaks seem to appear overnight.

Are spider mites harmful to pets and people?

Spider mites themselves are not directly toxic to pets or people. The risk is from chemical sprays used to control them — use insecticidal soap, horticultural oil, or biological control wherever possible. Always check the product label for re-entry and harvest interval guidance, and confirm the active ingredient is currently approved via the UK HSE register or US EPA.

What plants do spider mites not affect?

Spider mites most commonly affect tomatoes, cucumbers, beans-bush, roses. Plants with thick, waxy, or hairy foliage typically resist this pest better than soft-leafed crops. For pet-safe houseplant alternatives that resist most common pests, see our pet-safe houseplants guide.

Can I use the same protocol indoors and outdoors?

The biological-control choices change (indoor releases of ladybirds rarely work; predatory mites and parasitoid wasps do), but the spray protocols (insecticidal soap, horticultural oil, neem) translate directly. Outdoor cases benefit from reflective mulches and companion planting; indoor cases benefit from quarantine and routine wipe-downs.

Sources

Identification and control guidance sourced from US Cooperative Extension publications (UC IPM, NC State, UMD, UMN, Penn State, CSU, UF/IFAS EDIS), Clemson HGIC fact sheets, Royal Horticultural Society guidance, and Cornell NYS IPM Biocontrol fact sheets. Reviewed by the Growli editorial team in May 2026.

Keep going

• Spider mites — full kill protocol (article)
• All 8 garden pests covered in this guide
• Garden pest identification — complete article
• Companion planting chart (pest-deterrent pairings)
• Common houseplant diseases