Why Is My Fig Tree Covered in Sticky Brown Lumps?

If you notice brown, grey or tan-coloured crusty or waxy lumps adhering to the bark, stems and sometimes the undersides of leaves of your fig tree, accompanied by sticky residue on the surrounding surfaces, the tree has a scale insect infestation. Scale insects are sap-sucking pests that live beneath a protective shell or waxy covering, making them harder to deal with than more exposed insects. On container-grown figs kept indoors or in a greenhouse, scale infestations can become severe quite quickly without the natural predator pressure that exists outdoors.

Types of scale on figs

Two main types of scale insect affect fig trees. Soft scales (such as brown soft scale, Coccus hesperidum) produce a soft, waxy covering and excrete large quantities of honeydew, leading to black sooty mould on the leaves and bark below. Hard or armoured scales (such as fig scale, Lepidosaphes fici) form a more rigid shell and produce less honeydew. Both types weaken the tree by extracting sap and, in heavy infestations, can cause yellowing, die-back and fruit quality reduction.

Manual removal

For small to moderate infestations on accessible wood, manual removal is effective. Scrub the affected bark with an old toothbrush or stiff-bristled brush dipped in a solution of warm water and a small amount of insecticidal soap. This physically removes and kills the scale insects. Work along the stems methodically, paying particular attention to the junction between branches and to any crevices in the bark where colonies concentrate. Repeat after two to three weeks to catch any missed individuals or newly hatched crawlers.

Insecticidal treatments

Insecticidal soap spray, plant oils (such as neem or plant-based mineral oil) or a dedicated scale insect spray penetrate or smother the soft scale's covering and are effective against the crawler (juvenile) stage. The crawler stage, when the insects are mobile and have not yet formed their protective covering, is the most vulnerable. In the UK, crawlers emerge in late spring and summer. Treat at this time for the best results. Apply spray thoroughly to all bark surfaces, including any crevices.

Improving conditions to prevent reinfestation

Scale insects are strongly associated with stressed trees — particularly those that are under-watered, over-crowded or growing in poor light. A fig tree in excellent health with good air circulation and adequate light is less prone to severe infestations because the conditions favour the natural predators (ladybirds, parasitic wasps) that keep scale populations in check. Keep container figs well-fed and correctly watered, and move them outdoors in summer where natural predators can assist.