Geranium bronze: recognising damage on pelargoniums

The small brown butterfly hovering around a pot of pelargoniums may be the geranium bronze, Cacyreus marshalli. Its wings are patterned with cream-brown lines and each hindwing has a short tail. The adult does little direct harm, but its larvae feed inside buds and stems and can reduce a vigorous plant to hollow, collapsing growth.

The species originated in southern Africa and is now established around much of the Mediterranean. Zonal and ivy-leaved pelargoniums are its principal garden hosts. The familiar name "geranium moth" is misleading twice over: it is a butterfly and most affected patio plants belong to Pelargonium, not the hardy Geranium genus.

Read the plant before treating it

Eggs are laid singly on tender leaves, flower buds or stems. Young larvae may begin in a bud or leaf, then enter a stem and feed along its soft centre. Look for small entry holes, dark frass, damaged flower clusters and shoots that wilt although the compost is moist. Splitting a suspect stem lengthways may reveal a yellow-green, lightly hairy caterpillar or an empty gallery.

Not every weak pelargonium has this pest. Heat stress, waterlogged roots and fungal disease can also cause yellowing or collapse. Confirming a hole or larva avoids unnecessary treatment.

A practical control sequence

1. Inspect new pelargoniums before placing them beside an established collection.
2. Remove affected buds and cut hollow stems back to sound tissue. Put infested material in household waste rather than home compost.
3. Check remaining shoot tips regularly through warm weather, when repeated generations can overlap.
4. Keep plants appropriately watered and fed so that healthy growth is easy to distinguish from new damage.

Insecticides are not a complete answer because a larva inside a stem is protected from contact sprays. If damage remains severe, ask a Spanish garden centre or the regional plant-health service about products currently authorised for ornamental plants and follow the label exactly. Never use an agricultural product or an old recommendation simply because it names caterpillars.

Sources and review

This guide was reviewed in August 2026 using the European and Mediterranean Plant Protection Organization record for Cacyreus marshalli and the Royal Horticultural Society identification and control guide.