citrus blackfly

Symptoms

Black slipper-shaped scales (the nymphal stage — very distinctive) on undersides of citrus leaves, copious honeydew + black sooty mould on leaves + fruit + ground beneath trees, leaf yellowing + premature drop, branch dieback in heavy infestations, fruit downgrade from cosmetic damage.

Easily confused with

• Asian citrus psyllid (HLB vector)
• brown soft scale

  How to tell them apart: Citrus blackfly (Aleurocanthus woglumi) appears as clusters of jet-black, oval nymphs covered in stiff, spiny bristles, packed tightly in neat circular or spiral arrangements on the UNDERSIDE of leaves, often with a fringe of white waxy threads around each nymph. Brown soft scale (Coccus hesperidum) instead shows flat, smooth, oval shells that are translucent yellow-brown to tan (never spiny, never jet-black), scattered irregularly along leaf midribs and stems. Both drip honeydew and grow black sooty mould, but the spiny black armoured colonies of blackfly contrast sharply with the smooth, flat amber scales. If you see the dense black spiny nymph colonies, treat it as suspected citrus blackfly — a notifiable EU quarantine pest — and report it to your national plant protection organisation (NPPO) before applying any treatment.