Brown scale

Identification

A soft scale whose females form brown, dome-shaped, strongly convex "cups" (3–6 mm) sitting motionless on shoots, twigs and leaf bases. They suck sap, weakening the plants, and excrete abundant honeydew on which black sooty mould develops, disfiguring leaves and fruit. It feeds on fruit trees (plum, peach), grapevine, ornamental shrubs and houseplants. It belongs to the soft scales (Coccidae), not to the true armoured scales — its brown shield is the sclerotized body of the female and cannot be separated from her. In the Polish climate it usually develops one generation per year. It overwinters as an immature larva (second instar) attached to shoots and twigs, in bark crevices and near the buds. In spring the larvae resume feeding and the females grow quickly, turning into the characteristic, hardening "cups". Beneath its shield the mature female lays numerous eggs — often from several hundred to over a thousand. The crawling larvae (so-called crawlers) that hatch from them, usually at the turn of June and July, spread out onto the leaves and young shoots, where they attach and feed; before leaf fall they return to the shoots to overwinter. Symptoms of infestation are weakened growth and dieback of twigs under heavy attack, sticky, glossy honeydew on the leaves and beneath the plant, a black sooty coating that hampers photosynthesis, and numerous ants feeding on the honeydew. The larvae and females cluster in the forks of twigs, on the undersides of shoots, at the base of the leaves and along the veins and leaf stalks.

Treatment

Brushing and scraping the scales off shoots by hand, cutting out heavily infested twigs, and spraying with oil products (paraffin oils) during the leafless period or against the crawling larvae. It is worth curbing ants, which protect scale insects for their honeydew, and encouraging natural enemies (ladybirds, parasitic wasps). The timing of the treatment is crucial: mature females hidden beneath the hard cup are only weakly susceptible to contact products, so sprays are aimed at the leafless period (oils against the overwintering larvae) or at the time of hatching and crawler migration — usually at the turn of June and July — when they do not yet have a shield. On houseplants and single shrubs the most reliable approach is patient, mechanical removal of the shields (a brush, a damp cloth, spot wiping) combined with isolating the infested plant; it is effective but labour-intensive and hardly practical on large trees. Thinning cuts improve air circulation in the crown and make it easier to cover the shoots thoroughly with spray. Fitting sticky bands on the trunk cuts ants off from the honeydew, so that ladybirds (e.g. Chilocorus, Exochomus) and parasitic wasps regulate the population more effectively — this is, however, a support measure and not a stand-alone method under heavy infestation. Once the insects are already hidden beneath their shield, only products with systemic (translaminar) action, moving in the plant's sap, reach them despite the scale.

How to tell it apart from look-alikes

Control — organic and chemical methods

We give active-ingredient groups and modes of action, not brand names — specific products and their approval vary by country and are sometimes withdrawn. Always check and follow the current label.