Plant problem diagnostic key
Answer whatever you can — every question is optional. Causes that can actually kill the plant are flagged, so you know which to rule out first and which can safely be left alone.
Check these two things first
- Push a finger into the soil, two knuckles deep. Wet soil plus a wilting plant means too much water, not too little — and it is the commonest reason a plant is dying. Dry soil plus crisp leaves means the opposite. The leaves look nearly identical either way, so the soil is what tells you.
- Turn a damaged leaf over. Half of all diagnoses live on the underside: fuzz means downy mildew, fine webbing means spider mites, clusters of insects mean aphids. Nothing on the top of a leaf is as informative.
Most garden problems are cosmetic and resolve without treatment. Reach for a spray last, not first.
1.What plant is it?
optionalMany problems are specific to one family, so this removes a large share of the list straight away.
2.What does it look like?
optionalPick everything you can see. Any one match keeps a cause on the list, because you rarely see the whole picture at once.
3.Which part is affected?
optionalIf the roots are involved you will have to unpot or dig to find out — and with a declining plant that is usually the most informative thing you can do.
4.Where did it start?
optionalThe most underused question in plant diagnosis. Trouble that begins at the bottom means something very different from trouble that begins at the top.
- Bacterial WiltAct nowBacterial disease
- Cucumber BeetlesAct nowPest
- Downy MildewAct nowFungal disease
- Fusarium WiltAct nowFungal disease
- Herbicide DamageAct nowGrowing conditions
- Late BlightAct nowFungal disease
- Mosaic VirusAct nowVirus
- OverwateringAct nowGrowing conditions
- Root RotAct nowFungal disease
- Spider MitesAct nowPest
- Squash Vine BorerAct nowPest
- Verticillium WiltAct nowFungal disease
- AnthracnoseTreatableFungal disease
- AphidsTreatablePest
- Bacterial Leaf SpotTreatableBacterial disease
- Black SpotTreatableFungal disease
- Blossom End RotTreatableNutrient problem
- Cabbage Worms & LoopersTreatablePest
- Early BlightTreatableFungal disease
- Flea BeetlesTreatablePest
- Grey Mould (Botrytis)TreatableFungal disease
- Iron ChlorosisTreatableNutrient problem
- Japanese BeetlesTreatablePest
- MealybugsTreatablePest
- Nitrogen DeficiencyTreatableNutrient problem
- RustTreatableFungal disease
- Scale InsectsTreatablePest
- Septoria Leaf SpotTreatableFungal disease
- Slugs & SnailsTreatablePest
- Squash BugsTreatablePest
- ThripsTreatablePest
- Tomato HornwormTreatablePest
- UnderwateringTreatableGrowing conditions
- WhitefliesTreatablePest
- Fungus GnatsMostly cosmeticPest
- Powdery MildewMostly cosmeticFungal disease
- Sooty MouldMostly cosmeticFungal disease
- SunscaldMostly cosmeticGrowing conditions