Magnolia Scale
Magnolia scale is the largest soft scale insect in North America, with adult females reaching up to half an inch across. It feeds almost exclusively on magnolia species and, occasionally, tulip trees. Gardeners with ornamental magnolias should know this pest by sight, because heavy infestations can weaken branches, spur sooty mold growth across bark and foliage, and attract ants that disrupt the natural enemies that would otherwise keep populations in check.
The insect completes one generation per year. Tiny crawlers emerge from beneath mature females in late August and September, move to young twigs, and spend the winter as first-instar nymphs. In spring they resume feeding, gradually enlarging through the summer until females are fully mature by late July or early August. The females are dome-shaped, pinkish to brownish, and coated in a waxy bloom that makes them easy to see on bark with the naked eye. They excrete large quantities of honeydew, a sugary waste product that accumulates on bark and leaves and serves as the growing medium for black sooty mold fungi.
Parasitic wasps and predatory beetles provide meaningful biological control where broad-spectrum pesticide use has not eliminated them. Ant management and reduced pesticide inputs can allow these natural enemies to suppress scale populations without additional intervention.
Magnolia scale is a sap-feeding pest that extracts phloem contents from magnolia stems, promotes sooty mold through honeydew production, and can cause branch dieback under sustained heavy infestations.
Large brown or pinkish bumps clustered on twigs and young branches. Sticky honeydew coats leaves below, often followed by black sooty mold and stunted growth.
Prune out and destroy heavily infested twigs. Apply horticultural oil to smother crawlers in late summer and dormant oil in early spring. Monitor annually since populations rebuild slowly.