Soft scales

Soft scales (family Coccidae) are a widespread group of plant-sucking insects characterized by the lack of a separate protective shield, which distinguishes them from armored scales. Instead, their body wall itself hardens and serves as protection. These pests are significant threats to global agricultural and horticultural production due to their ability to colonize a vast array of host plants.

The host range of soft scales is extensive, impacting various important species. In agricultural settings, they are known to infest apple (Malus domestica), plum (Prunus domestica), forage beet, winter barley, common hop, alfalfa, tobacco, and field peas. By colonizing stems and foliage, they systematically drain the host plant of essential sap throughout the growing season.

The biology and lifecycle of these insects are defined by stages including egg, crawler (nymph), and adult. Adult females are sessile, remaining attached to the plant surface, where they lay hundreds or thousands of eggs under their protective dorsal cuticle. The mobile crawler stage is the primary period for dispersal within and between plants, often aided by wind or animal contact.

Damage caused by soft scales is twofold: direct feeding damage and indirect secondary effects. Direct feeding leads to chlorosis, stunted plant growth, and branch dieback. Furthermore, these insects excrete large quantities of honeydew, which fosters the growth of sooty mold. This layer of mold blocks sunlight from the leaves, severely hindering photosynthesis and reducing overall crop quality and yield.

Management of soft scales relies on integrated pest management (IPM) practices. Chemical control is most effective during the crawler phase when the insects lack a tough protective covering. Cultural practices, such as pruning infested wood, ensuring proper plant nutrition to boost host resistance, and encouraging populations of natural predators like lady beetles and parasitic wasps, are essential for long-term population suppression.

• Regular monitoring for crawler emergence.
• Targeted application of horticultural oils.
• Maintaining healthy plants through balanced fertilization.
• Removal and destruction of heavily infested plant parts.