Raspberry crown borer

The raspberry crown borer (Pennisetia marginata) is a significant pest of bramble fruits, belonging to the family Sesiidae and the order Lepidoptera. Adult moths are clearwing moths that exhibit mimicry, closely resembling hornets or yellowjackets. While adults are harmless to plants, their larvae are highly destructive to raspberry and blackberry crowns.

The larvae bore into the crown and roots of the host plants, which is the most critical area for plant development. As they feed on the internal tissues, they disrupt the vascular system, significantly weakening the plant. This damage makes the canes susceptible to secondary diseases and winter cold, eventually leading to the death of the plant.

The life cycle of this pest spans two years. Female moths lay their eggs on the undersides of leaves during the late summer. Once hatched, the larvae crawl down to the soil and bore into the base of the cane or crown to overwinter. During the second year, they feed extensively, causing the characteristic damage before pupating in the spring.

Infestation symptoms include stunted growth, yellowing or wilting of the leaves, and canes that break off easily at the base. Growers may notice small entrance holes or frass (larval excrement) near the crown of the plant. A close inspection often reveals internal tunneling within the crown area, which is a definitive sign of an active borer population.

Effective management requires an integrated approach. The most crucial step is the physical removal and destruction of infested plants, including the roots, to kill the larvae before they emerge. Maintaining good plant vigor through proper fertilization and irrigation helps plants withstand low-level infestations. Chemical control, if necessary, should be timed with the egg-laying period.

• Manual removal and destruction of infested canes and crowns.
• Monitoring for adult flight periods using pheromone traps.
• Avoiding the use of infested nursery stock.
• Applying targeted insecticides to the base of canes when larvae are active.