A common pest known as euonymus scale has been identified as the cause of white spots appearing on pachysandra plants, according to experts at the Chicago Botanic Garden. This marks a rare occurrence of the infestation on pachysandra, which typically affects other plant species.

Euonymus scale insects damage plants by piercing the sap-bearing tissues with their specialized mouthparts, weakening the host over time. Control of this pest is challenging because adult scales secrete a protective, waxy covering that shields them from many insecticides.

The pest’s life cycle provides key opportunities for management. Female scale insects overwinter on the plant and begin laying eggs during late April and May. These eggs hatch into mobile “crawler” forms over a two- to three-week period. Crawlers are the most vulnerable stage for intervention, as they have yet to develop protective coverings. A second generation of crawlers appears from late July through August.

Experts advise that no immediate action is necessary during the winter months. However, pruning and removing infested sections of pachysandra in early spring—preferably by March—can eliminate overwintering adults and reduce future populations. Discarding plant material in commercial landscape waste facilities that reach sufficient heat levels is recommended to ensure pest destruction.

During the active crawler stages in late May to early June and again in late July through August, the application of summer-weight dormant oils is the preferred control method. Dormant oils can smother the vulnerable crawlers and help manage infestations when timed appropriately.

Gardeners encountering similar symptoms or seeking further guidance are encouraged to reach out to the Plant Information Service at the Chicago Botanic Garden for expert advice.