Raspberry Crown Borer

Raspberry Crown Borer, (Pennisetia marginata) is the most devastating pest of blackberry and raspberry in Kentucky. While not as obvious as Japanese beetle or green June beetle attacking the fruit, raspberry crown borer attacks the roots and crown of the plants and can result in killed or weakened canes.

Raspberry crown borer symptoms include canes prematurely dying, spindly cane growth, and reduced leaf size. If you suspect raspberry crown borer, look for sawdust-like frass pushed out of the base of infested canes near the soil, swelling at the base of the canes, or tunnels in the canes that are noticed while pruning. This is a common pest of blackberries and raspberries throughout the state that can severely reduce the productivity of a planting.

Life Cycle: Eggs are laid on the undersides of new leaves, with 2-3 eggs per plant. Eggs incubate 3-10 weeks, beginning to hatch in late July about the first week of September and continuing until early November in the northern part of its range. The young larva spins down to the crown, where it overwinters in a hibernaculum.

In the spring it tunnels into the cambium. Cracks develop at this site, from which reddish brown frass is produced in April. During the first summer, the larva feeds at the base of new canes, girdling the plant and causing gall formation. Galls are most evident in October. There is two-year life cycle. In the second summer, the larva ascends into a cane, girdling it a few inches above the soil surface, and causing it to wilt and break.

The pupal stage occurs in late June to early August. Moths fly from early to mid July through late September (August through September in the north). Females begin to oviposit beginning on the first day after emergence; the female lives 3-11 days, averaging about 103 eggs.

Damage: Damage from this serious pest can often be confused with root rot and wilt diseases. The first indication of injury is the withering, wilting and dying of the cane foliage, often with half-grown fruit still attached. Damaged canes will often break at the damaged area when pulled, revealing the larva inside. In New England, swelling of the crown has also been observed. In severe cases, the infested plant may die. The crown must be dug and opened to find the larva infesting it.

Controls: The best way to manage the raspberry crown borer is to prevent its intrusion into the caneberry field through the cultural controls. In the event that this pest establishes itself in the field, the chemical controls below may prove useful.

Biological Control: There is no commercially acceptable biological control for raspberry crown borer in the field at this time.

Cultural Control: The use of clean planting stock is necessary to reduce the movement of infested plant stock from one field to another. The removal of wild blackberries surrounding the field can help reduce populations of raspberry crown borer. Monitoring this pest is difficult because it is hidden away in the crown of the plant. By the time the damage is noticed, it is too late to do anything effective. If a population becomes established in the planting, treatments may be warranted.

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