What this checker does
This checker takes the symptoms you can see on a plant and suggests the most likely causes, with a practical first step for each.
It works on visible signs rather than identification, because most gardeners see the damage long before they see whatever caused it. Several symptoms have more than one likely cause, and the checker lists them all rather than picking one.
Visible symptoms
Likely causes
Before you treat anything
- Look at the plant closely first, including leaf undersides and stem joints, and preferably at dusk for slugs and at midday for aphids.
- Check watering and drainage before assuming a pest. Yellowing and wilting are far more often cultural than biological.
- Identify before you treat. Broad-spectrum treatments kill beneficial insects, which frequently makes the original problem worse.
- Most healthy plants tolerate some damage. Not every problem needs intervention.
A plant that wilts while the soil is wet is not short of water — it cannot take it up. That points to root damage, root rot from waterlogging, vine weevil larvae in a container, or stem damage. Watering more makes it worse, which is why checking the soil before reaching for the can matters.
How this calculator works
Symptom to likely cause, with overlaps kept:
Holes or slime trails → slugs, snails or caterpillars
Sticky residue or distorted growth → aphids or scale insects
Fine webbing → spider mites
White powder → powdery mildew
Yellowing or wilting → watering, drainage or root problemsWhere several symptoms point at different causes, all matching suggestions are shown. That is deliberate — a plant can have two problems at once, and aphids frequently accompany the sooty mould their honeydew supports.
The checker covers common garden and houseplant problems. It does not cover viral diseases, nutrient deficiencies or the many pests specific to particular crops.
Worked example: sticky leaves and distorted growth
Selecting sticky leaves and distorted new growth returns aphids or scale insects, with the advice to inspect stems and leaf undersides.
Both symptoms come from the same mechanism: sap-sucking insects distort the growing tip they feed on, and excrete honeydew that makes leaves sticky and later goes black with sooty mould. Finding the insects confirms it — and often finding nothing means they have already gone, since the damage persists after the cause has left. Adding holes in leaves to the selection would return slugs alongside, which is a genuinely different problem needing a different response.
Common mistakes
- Treating before identifying. The wrong treatment wastes effort and can harm beneficial insects.
- Assuming yellow leaves mean a deficiency. Overwatering is the more common cause.
- Spraying aphids on sight. Ladybirds, hoverflies and birds usually deal with them within a fortnight.
- Watering a wilting plant without checking the soil. Wet soil and wilting means a root problem.
- Missing the underside of leaves. Most sap-sucking pests live there.
Frequently asked questions
Should I use pesticides?
Sparingly and specifically, if at all. Broad-spectrum insecticides kill ladybirds, hoverfly larvae and parasitic wasps as readily as the pest, which removes the natural control and often leads to a worse outbreak. Physical removal, barriers, encouraging predators and simply tolerating some damage handle most garden problems.
What are the safest slug controls?
Hand collection at dusk after rain is the most effective and is free. Barriers, beer traps and encouraging hedgehogs, frogs and birds all help. Metaldehyde slug pellets have been withdrawn from sale in the UK because of the risk to wildlife; ferric phosphate pellets remain available and are considered lower risk.
Why do my houseplants get spider mites?
Dry warm air, which is normal in a heated house in winter, suits them well. Raising humidity by grouping plants, standing pots on damp gravel trays and misting reduces the problem considerably. Isolate an affected plant, since they spread readily, and rinsing the foliage physically removes a large proportion.
When should I get expert help?
For anything affecting a valuable tree, anything spreading rapidly through several plants, or any suspected notifiable plant disease. The RHS provides advice to members, and Defra publishes guidance on plant health and reportable pests and diseases, some of which must legally be reported.
Is what I select stored?
No. Your selections are processed in your browser and never transmitted or retained.
Related tools
References
- Royal Horticultural Society — plant pest and disease identification and management advice
- GOV.UK — plant health, notifiable pests and pesticide regulation
Sources are checked at publication and can change — how I choose and check references.