Q What is viburnum beetle?
A An inconspicuous beetle that nibbles holes in viburnums when it's both a grub and an adult.
Caption: The grubs hatch in spring and nibble viburnum leaves
Q How do I recognise it?
A Most damage is done by the grubs or larvae which are yellow, about 5mm long, with fine black lines and spots. The beetles are yellowish-brown, covered in short golden hairs and also about 5mm long.
Q Why is it becoming more common?
A Viburnum beetle (Pyrrhalta viburni) is native to Britain, but it has become more prevalent in recent years, possibly because warmer winters have allowed the eggs to survive in larger numbers. It is mostly a problem in the south and midlands, and it is much rarer in the north.
Q What plants does it attack?
A Until fairly recently it was only found feeding on our wild viburnums: the guelder rose (Viburnum opulus) and wayfaring tree (V. lantana) and their cultivated varieties. It then moved on to the popular and widespread evergreen laurustinus (V. tinus), and has recently started to attack other species of viburnum too.
Q What damage does it do?
A The damage is distinctive, consisting of a large number of irregular holes eaten between the veins of the leaf, which eventually takes on a lace-like appearance. Damage is concentrated on young shoots.
Q Could I mistake it for anything else?
A Beetles or grubs feeding on viburnum are unlikely to be any other species. They also produce a foul smell, noticeable in hot weather. The appearance of the damaged leaves is also very distinctive. Slug or caterpillar damage generally results in fewer, larger holes.
Q How serious is it?
A In terms of the plant’s survival, attacks by the beetle are not that serious and, on regularly clipped plants, such as a laurustinus hedge, most of the damage will be cut away. However, on untrimmed plants the damage can be very unsightly.
Q What is its life cycle?
A The beetles lay eggs in holes cut into the bark in late summer. The eggs overwinter, and the larvae hatch in the spring.
By mid-May the larvae are feasting on the new foliage, and in June they move down to the soil to pupate. The adults emerge in July and August.
Q When do attacks occur?
A Most damage occurs in late spring and early summer when the larvae are feeding heavily. Adults do some damage in mid- to late summer.
Q How do I control an attack?
A You can squash or pick off the larvae and adults by hand, or you can remove and bin or burn the infested shoots.
Alternatively, you can spray the larvae from mid-April to early May with any insecticide recommended for a broad spectrum of plant pests. These could include Westland Plant Rescue Fruit & Vegetable Bug Killer, Scotts Bug Clear Gun for Fruit & Veg (organic) or Py Spray Garden Insect Killer (organic).
There is, however, no point in treating damaged plants after the larvae have left to pupate, which is when the damage is at its most obvious. If, after treatment, adults arrive from neighbouring gardens you may need to treat again in summer, though the adults are less susceptible to sprays than the larvae.
Q What should I do with affected plants?
A Trim off the most badly damaged shoots to improve appearance and encourage new growth.