Raspberry beetle (Byturus tomentosus)
A serious pest of all the cane fruit, the 4mm long brown raspberry beetle is rarely seen while it feeds on and lays its eggs on the flowers from May to July. The creamy-white grubs, which eventually grow to 8mm long, can also be difficult to spot. They begin by eating near the stalk end of the fruit, and it is here that damage is often most apparent. They then move into the ripening fruit before dropping to the soil when mature - this is where they overwinter, emerging in April/May as adults. The timing of egg-laying means that autumn fruiting canes are less affected than summer fruiting varieties. Damaged fruit may develop secondary infections.
- Brown, dry, shrivelled 'drupelets', particularly near the stalk
- Secondary fungal infections such as grey mould
- At harvest time, the grub may be visible, either in the fruit, or trying to escape from fruit in the bowl!
Prevention & control
- Remove mulches over the winter and hoe (carefully - raspberries are shallow rooted) around canes to expose overwintering grubs
- Check for, remove and destroy affected fruit - stalk, core and all - before the grubs emerge
- Traps, which lure the beetles to their death with the scent of raspberries may control light infestations and help indicate whether spraying is necessary. They are placed 4-6 weeks before flowering (April-July, depending on variety) to catch the beetles before they can lay their eggs.
- Pyrethrum sprays can be effective but timing is crucial and varies from fruit to fruit. The idea is to catch them while they are still accessible:
- Raspberries: when the first pink fruit appear, spray again two weeks later
- Hybrid berries: at 80% petal fall, spray again two weeks later
- Blackberries: just as first flowers open