African scale

African scale (Diaspidiotus africanus) is a member of the Hemiptera order and the Diaspididae family. It is a highly specialized sap-sucking pest that poses a significant threat to agriculture and horticulture. Its ability to form protective layers makes it particularly difficult to manage in commercial fruit production.

This pest attacks a diverse range of hosts, primarily focusing on pome and stone fruits, as well as various citrus and ornamental species. Infestations are typically found on the bark of trunks and branches, but under high pressure, the insects can spread to leaves and fruit surfaces, causing significant cosmetic and physiological damage.

The life cycle of Diaspidiotus africanus involves an egg stage, the mobile 'crawler' stage, and the sedentary adult stage. Crawlers are the primary dispersal mechanism, moving to new sites to settle and feed. Once settled, they secrete a wax-based scale cover that protects them from environmental stressors and many contact pesticides.

The damage caused by the African scale includes chlorosis of leaves, stunted growth of shoots, and overall tree decline. As the insects feed, they inject toxic saliva, which leads to localized necrosis and pitting on fruits. Severe infestations often result in reduced photosynthesis, fruit drop, and in extreme cases, the mortality of young trees.

Management strategies for this pest are essential for maintaining orchard health. Key approaches include:

• Rigorous nursery stock inspections to prevent new infestations.
• Dormant oil applications to target overwintering females.
• Targeted insecticide treatments synchronized with the peak crawler emergence.
• Promoting natural biological control agents such as parasitic wasps.