What's eating my lemon tree?

Lemon trees grown indoors or in pots are attacked by scale insects (the biggest threat), mealybugs in leaf axils, spider mites in dry conditions, and aphids on new flushes of growth. Outdoors, citrus leafminer tunnels young leaves. Scale insects are the most damaging and most commonly encountered pest across all growing conditions.

Brown, waxy, limpet-like scales encrust stems, leaf undersides, and fruit; they suck sap continuously, causing yellowing leaves, die-back of twigs, sticky honeydew, and heavy sooty mould coating all surfaces. Scrub light infestations off with a soft brush dipped in soapy water; apply horticultural oil spray in late winter (outdoors) or year-round (indoors) to suffocate scales; introduce Metaphycus helvolus parasitic wasps in glasshouses.

White, fluffy wax masses in leaf axils, fruit stalks, and hidden stem crevices; sap-sucking causes leaf yellowing and drop; heavy infestations weaken the whole tree. Dab colonies with alcohol-soaked cotton swabs; drench soil with dilute neem oil to target root mealybugs; apply insecticidal soap to foliage; introduce Cryptolaemus montrouzieri ladybird beetle in protected conditions.

Silvery, winding mines trail through the surface of young leaves; affected leaves curl and are distorted; primarily cosmetic on established trees but can stress young trees. Remove and destroy affected young flush growth; apply spinosad spray as new leaf flushes emerge; avoid heavy nitrogen feeding in late summer which stimulates vulnerable new growth.

Reddish mites cause fine grey or silvery stippling on both leaf surfaces; in severe infestations leaves yellow, bronze, and drop; fruit skin develops a silvery russeting. Spray forcefully with water; apply neem oil or insecticidal soap; maintain good humidity around the plant; introduce Phytoseiulus persimilis in controlled indoor conditions.