Aphid and Ant Infestation on Meyer Lemon: Identification and Control

Aphid and Ant Infestation on Meyer Lemon: Identification and Control

A Meyer lemon tree has "egg-like things" on leaves, blackish trunk discoloration, and ants crawling all over. The owner applied Sevin dust.

Diagnosis

• The "egg-like things" are aphids (likely colonies of nymphs and adults).
• Ants farm aphids for their honeydew (sugary excretion).
• Black discoloration on trunk is sooty mold growing on honeydew—not a disease itself.
• Sevin (carbaryl) is a broad-spectrum insecticide; it kills beneficials too. Not ideal for edibles.

Control Options

Organic / Low-Impact

• Blast with water: Strong jet dislodges aphids.
• Insecticidal soap / neem oil: Spray thoroughly, especially undersides. Repeat weekly.
• Ant barrier: Apply sticky band (Tanglefoot) on trunk to block ant access. Without ants, natural predators (lady beetles, lacewings) control aphids better.

Systemic Insecticides (if needed)

• Imidacloprid (soil drench) – moves into vascular tissue; aphids die when feeding. Do not apply during bloom (harms bees). Follow label for pre-harvest interval.
• Dinotefuran – faster uptake, similar restrictions.

Trunk Discoloration

The black sooty mold will weather off once honeydew stops. It does not penetrate bark. The lichens mentioned in another answer are unrelated—they are greenish, not black.

Key Point

Aphids are attracted to vigorous, nitrogen-rich growth. They are a natural part of the ecosystem. Treatment is only needed when populations cause visible damage (curling, stunting, sooty mold).