Western cottony scale

The Western cottony scale (Pulvinaria occidentalis) is a member of the soft scale family (Coccidae) within the order Hemiptera. It is a persistent sap-sucking pest that poses a significant threat to various fruit and ornamental tree species across various temperate regions.

The host range of this pest primarily includes fruit trees like apples, pears, and plums, as well as several ornamental and wild shrubs. Due to their ability to feed on woody stems, they can establish dense populations on mature trees, particularly in orchards where chemical control is not properly timed.

The biology of Pulvinaria occidentalis is characterized by a univoltine or bivoltine life cycle depending on the local climate. Adult females produce distinct white, cotton-like ovisacs that house hundreds of eggs. Once hatched, the mobile nymphs, known as crawlers, disperse across the plant to find suitable feeding sites on the bark.

The damage caused by the Western cottony scale is twofold. First, they extract essential plant fluids, which reduces the vigor of the tree and can lead to branch dieback. Second, they excrete large amounts of honeydew, which promotes the growth of sooty mold, blocking sunlight from the leaves and interfering with photosynthesis.

Control strategies for this pest should focus on integrated management:

• Apply horticultural oils in late winter or early spring to smother overwintering nymphs.
• Use systemic insecticides specifically targeting the crawler stage when they are most vulnerable.
• Practice regular pruning to remove infested branches and improve tree health.
• Conserve natural enemies such as lady beetles and parasitic wasps, which can help regulate scale populations in organic settings.