Garden pest identification — the complete guide

Garden pest identification — the complete guide

Almost every pest call we get falls into one of eight species groups. Two more are crop-specific and covered in their own guides — the tomato hornworm that strips nightshade foliage overnight, and the Japanese beetle that skeletonises roses, beans and grapes — but the eight in this article cover home vegetable beds, ornamentals, herb pots, indoor foliage, and citrus. This is the field guide we use ourselves — what to look for, where it lives, and the 3-week IPM protocol that clears each one without wrecking pollinators or your soil.

Try Growli: Snap a photo of the bug or the damaged leaf and Growli will confirm the species, cross-reference it against your specific plant, and schedule the protocol reminders for you. Identification is the half of pest control that nobody gets right alone — see also our /pests programmatic guide for pest × crop pairs.

How to identify garden pests in 30 seconds

Three quick questions cover roughly 90% of cases:

1. Where on the plant is the pest sitting? Top of leaves and stems means aphids, thrips, or whitefly. Underside of leaves means spider mites, whitefly nymphs, or scale. Leaf joints and stem forks means mealybugs. Around the soil surface means fungus gnats or slugs. Hidden inside flower buds means thrips.
2. What has the pest left behind? Sticky honeydew points to aphids, whitefly, or scale. Fine webbing means spider mites. White cottony wax means mealybugs. Silvery slime trails mean slugs. Black faecal specks mean thrips. Damped-off seedlings mean fungus gnats (root chew) or slugs (top chew).
3. How does the pest move? Whitefly fly when disturbed. Aphids walk slowly. Spider mites are barely visible without a hand lens. Mealybugs barely move. Scale does not move at all. Slugs glide.

Combine those three answers and you usually have the species before you reach for a spray. The rest of this article walks through each pest in depth — but if you only remember one thing, it is the three questions above.

The 8 pests, ranked by how often we see them

1. Aphids — soft-bodied sap-suckers on new growth

Aphids are the most widespread pest in home gardens worldwide. They are 1-4 mm pear-shaped insects in green, black, pink, yellow, or grey, depending on species. They cluster on the youngest growth tips and on the undersides of upper leaves. They reproduce asexually, so a few become thousands within weeks.

Confirm: clusters of soft bodies on shoot tips, sticky honeydew on lower leaves, ant trails climbing the stem (ants farm aphids).

Kill in 7-10 days:

1. Blast the plant with a strong water spray every 2-3 days for 2 weeks.
2. Spray insecticidal soap or neem oil every 4-5 days for three weeks.
3. Release ladybugs or lacewing larvae for severe cases.
4. Prevent re-infestation with reflective silver mulch and a few alyssum or fennel plants to host hoverflies.

Aphids hit nearly every crop in the garden — see /pests/aphids for the full host list with per-crop protocols.

2. Spider mites — fine stippling and webbing in hot, dry weather

Spider mites are tiny arachnids (0.5 mm), barely visible to the naked eye. They thrive in hot, dry, dusty, drought-stressed conditions. Damage shows as fine yellow speckling on leaves, then a sand-blasted bronze look, then fine webbing in leaf axils.

Confirm: tap a leaf over white paper — moving specks confirm mites. Webbing on leaf undersides is unmistakable. Plants near south-facing walls, indoor heating vents, or dusty paths are most exposed.

Kill protocol:

1. Raise humidity around the plant (group plants, run a humidifier indoors, mist outdoor foliage).
2. Strong water spray under every leaf, every 3-4 days.
3. Insecticidal soap or horticultural oil weekly for three weeks.
4. For severe greenhouse cases, release Phytoseiulus persimilis predatory mites — the standard biocontrol since the 1960s.

Spider mites are particularly destructive on tomatoes, cucumbers, beans, and strawberries — see /pests/spider-mites for the full crop list.

3. Whitefly — clouds of tiny moth-like adults

Whiteflies are 1-2 mm white moth-like insects that fly up in a cloud when leaves are disturbed. Nymphs are scale-like and immobile on the underside of leaves. Both stages suck sap and excrete honeydew.

Confirm: disturb the canopy and watch — a cloud of tiny white fliers rising is unmistakable. Translucent oval scales on leaf undersides confirm nymphs.

Kill protocol:

1. Yellow sticky traps at canopy height — catch adults before they lay.
2. Silver reflective mulch around the base of plants (outdoor).
3. Remove the lowest leaves where most nymphs settle.
4. Insecticidal soap or horticultural oil on nymphs, every 5-7 days for three weeks.
5. Encarsia formosa parasitoid wasps for greenhouse tomatoes and cucumbers — the original commercial biocontrol agent, in continuous use since the 1920s.

4. Fungus gnats — damp-soil flies that kill seedlings

Fungus gnats are 2-3 mm dark flies that swarm around damp potting mix. Adults are harmless; larvae chew tender roots and seedling stems. They are by far the most common pest call on houseplants and indoor seedling setups.

Confirm: dark flies running across the soil surface (rather than flying like fruit flies, which prefer overripe fruit). Algal sheen on the top of the mix is a giveaway — soil is too wet.

Kill protocol:

1. Let the top 2-3 cm of mix dry between waterings.
2. Bottom-water seedling trays.
3. Top-dress with horticultural sand, grit, or perlite to block egg-laying.
4. Yellow sticky cards flat on the soil surface to trap adults.
5. Drench the mix with Bti (Mosquito Bits steeped in water, Bacillus thuringiensis israelensis) every 7-14 days.

5. Thrips — silver streaks and TSWV virus risk

Thrips are slender 1-2 mm insects that rasp the leaf surface and suck up the released sap, leaving silvery scars and tiny black faecal specks. Western flower thrips also vector tomato spotted wilt virus (TSWV), which is incurable once a plant is infected.

Confirm: silvery rasping marks plus tiny black specks on leaves. Tap a flower over white paper and slender brown adults will scurry.

Kill protocol:

1. Use thrips- and virus-free transplants. This is the single most important step — most TSWV outbreaks start with one infested seedling.
2. Blue or yellow sticky traps at canopy height.
3. Spinosad sprays at dusk (to protect bees).
4. Orius insidiosus (minute pirate bug) for pepper and cucumber greenhouses — banker plants of ornamental pepper 'Purple Flash' or 'Black Pearl' sustain reproducing Orius populations.

6. Mealybugs — white cottony wax in leaf joints

Mealybugs are 3-6 mm pink soft-bodied scale insects covered in white cottony wax. They cluster in leaf joints, on stems, around fruit calyxes, and sometimes on roots. They produce honeydew like aphids and whitefly.

Confirm: white cottony tufts in the joints between leaves and stems are the giveaway — no other common pest looks like this.

Kill protocol:

1. Dab adults with a cotton swab dipped in 70 percent isopropyl alcohol.
2. Rinse the plant under a tepid sink shower.
3. Spray insecticidal soap weekly for three weeks.
4. For severe infestations, release Cryptolaemus montrouzieri (mealybug destroyer) larvae — adults disperse, but larvae stay on the plant.

7. Scale insects — immobile bumps on stems

Scale insects are 1-5 mm immobile bumps stuck to stems and leaf undersides. Armoured scales have a hard shield; soft scales produce honeydew. They are most common on long-lived woody plants — citrus, roses, indoor figs, ornamental shrubs.

Confirm: the bumps do not move when prodded. Lift a bump with a fingernail — there should be a soft yellow body underneath. Yellow halos on leaves around each scale are a giveaway.

Kill protocol:

1. Time horticultural oil sprays for the crawler stage (newly hatched, wax-free nymphs). Use sticky tape on infested stems to detect first crawlers.
2. Spray oil at 1-2 percent during the spring crawler window, or 3-4 percent during dormancy on deciduous hosts.
3. Scrape adults off with a fingernail or soft brush on small infestations.
4. Aphytis melinus parasitoid wasps for California red scale on citrus; Metaphycus helvolus for soft scales.

8. Slugs — silvery trails and ragged holes

Slugs leave silvery slime trails and ragged, lacy holes in soft leaves and ripening fruit. They feed at night and in damp conditions, especially during cool spring and autumn weeks — our dedicated guide to controlling slugs and snails covers the full beer-trap, barrier and nematode arsenal.

Confirm: silvery slime on leaves and soil at dawn. Go out 1-2 hours after sunset with a torch — slugs will be on the move.

Kill protocol:

1. Hand-pick after dark for three consecutive nights (clears 60-80 percent of an active population).
2. Iron-phosphate pellets (Sluggo, Ferramol) around vulnerable crops — organic-approved and low-risk to pets and wildlife.
3. Copper foil or tape on raised bed edges.
4. Phasmarhabditis hermaphrodita parasitic nematodes (sold as Nemaslug in the UK) drenched into the soil.
5. Do not use metaldehyde slug pellets — they have been withdrawn from sale in the UK since 2022 and are restricted in many EU and US jurisdictions.

Quick-reference identification table

What to do when you can't tell the pest apart

Two pests look alike often enough to cause real confusion:

Aphids vs whitefly nymphs. Aphids have visible legs and walk slowly; whitefly nymphs are immobile, translucent, and oval. Disturb the canopy — if a white cloud rises, it is whitefly.

Mealybugs vs powdery mildew. Mealybugs are individual cottony tufts in leaf joints. Powdery mildew is a continuous chalky film across whole leaf surfaces. Mildew wipes off; mealybugs do not.

Scale vs harmless lichen. Scale has yellow halos around each bump, often with honeydew below. Lichen is grey or sage-green and does no damage to bark. Scale concentrates at twig terminals; lichen is uniform.

If you are still unsure after the visual check, snap a photo in Growli — instant species ID against a database of garden and houseplant pests, with the right protocol attached.

Integrated pest management — the gardener's playbook

Whatever pest you find, the playbook is the same:

1. Identify first. Wrong species means wrong protocol. Confirm before spraying.
2. Start non-chemical. Water blast, sticky traps, manual removal, reflective mulch, or quarantine clear roughly 60-70 percent of cases without a drop of pesticide.
3. Add biological control for long-cycle crops. Greenhouse tomatoes, cucumbers, peppers, indoor citrus, and protected strawberries 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.
5. Reserve stronger sprays for outbreaks. Spinosad, pyrethrin, and pest-specific options like Bti are second-line, not first-line.
6. Monitor weekly. Most populations rebound from a single intervention. Two or three weeks of follow-up checks separate a fixed problem from a recurrence.

The cardinal rule: never mix biological control with broad-spectrum chemical sprays. Pyrethroids and neonicotinoids wipe out predator releases on contact. Use one strategy at a time, or stagger them by at least a week.

Pesticide safety and approvals

Always read the product label and follow manufacturer's PPE, dosage, and re-entry guidance. Pesticide approvals change — confirm via the UK HSE pesticide register or US EPA before use.

Two regulatory shifts to know about:

• Neonicotinoids (imidacloprid, clothianidin, thiamethoxam) have been progressively restricted because of pollinator harm. The UK HSE rejected emergency authorisation in January 2025, and EU approvals lapsed. Most extension services no longer recommend them for home or commercial use on flowering crops.
• Metaldehyde slug pellets have been withdrawn from sale in the UK since 2022 (Defra ban) and are restricted in many EU and US jurisdictions. Use iron-phosphate pellets instead.

When to call a professional

For most home gardens and houseplant collections, the protocols above are enough. Reach out to a licensed pest professional only when:

• You have a confirmed outbreak of a notifiable plant pest (in the UK, see the Plant Health Portal; in the US, see USDA APHIS).
• You have a commercial-scale crop and need a licensed applicator.
• Multiple back-to-back protocols have failed and a soil-borne or systemic cause needs investigating.

For most home cases, identification plus a 3-week organic protocol is the entire answer.

Related articles

• How to get rid of aphids on plants
• Spider mites on houseplants treatment
• Fungus gnats — full kill guide
• Mealybugs on plants
• Scale insects — identification and control
• Common houseplant diseases
• Companion planting chart (pest-deterrent pairings)

Programmatic pest x crop pages

For the proven control protocol on a specific pest + crop combination, see the /pests programmatic guide. Highest-volume queries include:

• Aphids on tomatoes
• Aphids on roses
• Spider mites on tomatoes
• Whitefly on tomatoes
• Fungus gnats on seedlings
• Thrips on peppers
• Mealybugs on basil
• Scale insects on citrus
• Slugs on lettuce
• Slugs on strawberries

Reviewed and updated by the Growli editorial team. For questions about anything here, open Growli and ask — or email hello@getgrowli.app.