Treating Yellow Spots on a Dwarf Lisbon Lemon

Identifying the Issue

Your three-year-old potted dwarf Lisbon lemon in Arizona showed a growth spurt and flower buds, but now displays yellow spots on new growth. You recently started fertilizing with fish emulsion. The spots suggest sap-sucking insects—likely aphids, whiteflies, or spider mites—feeding on the undersides of leaves.

Recommended Treatment

1. Inspect leaf undersides with a magnifying glass. Look for tiny insects, webbing, or sticky honeydew.
2. Apply neem oil (preferred) or insecticidal soap. Neem oil has residual activity and deters a broad range of pests. Spray thoroughly, covering all surfaces, early morning or evening to avoid leaf burn.
3. Repeat weekly for 2–3 weeks to break the pest life cycle.
4. Continue fertilizing with fish emulsion (a good organic nitrogen source) but ensure the fertilizer includes phosphorus and potassium for flowering and fruiting.

Cultural Practices for Fruit Production

• Sunlight: 8+ hours of direct sun.
• Watering: Keep soil evenly moist; avoid letting the pot dry out completely.
• Pollination: Hand-pollinate flowers with a small brush if bees are scarce.
• Winter care: In Arizona, protect from frost by moving the pot to a sheltered spot.

With consistent pest management and proper care, your Lisbon lemon should set fruit within the next season.