Citrus problems
Yellow leaves on citrus are far more often a nutrient or watering problem than a disease. Which part of the leaf stays green tells you which nutrient is short.
Start from what you can see
Each of these has more than one possible cause, and each page separates them.
Everything that commonly affects citrus trees
Most serious first. Most of the list is treatable or can be ignored.
Pest
Fine even stippling rather than discrete spots or holes.
Pest
Dense clusters on new shoots and flower buds rather than scattered individuals.
Nutrient problem
Green veins on a yellow leaf — the net pattern is diagnostic.
Pest
White cottony specks in leaf axils and crevices.
Nutrient problem
Whole leaf yellows evenly, veins included.
Pest
Immobile bumps that scrape off with a fingernail, leaving a soft body.
Growing conditions
Leaves dry and crisp rather than soft and limp.
Fungal disease
Wipes off with a damp cloth, unlike any true leaf disease.
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.
Diagnose your citrus
Already filtered to citrus trees. Add the symptoms and where the trouble started.
1.What plant is it?
Many 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.
- Spider MitesAct nowPest
- AphidsTreatablePest
- Iron ChlorosisTreatableNutrient problem
- MealybugsTreatablePest
- Nitrogen DeficiencyTreatableNutrient problem
- Scale InsectsTreatablePest
- UnderwateringTreatableGrowing conditions
- Sooty MouldMostly cosmeticFungal disease