(Pyrrhalta viburni) Viburnum beetle is a serious pest of several species of viburnum. The larvae attack the leaves, causing severe defoliation of plants. Adult beetles also eat the leaves.
- Holes in the leaves, giving the appearance of lace doilies
- Brown, dried-up edges to the holes and the leaves
- Creamy-yellow grubs (larvae) with black markings on the leaves
- Greyish-brown adult beetles
What are viburnum beetles?
The adult beetles are greyish-brown in colour and measure 4-6mm (around 1/8in) long. They feed on the leaves in summer and early autumn.
The creamy-yellow larvae have black markings and measure up to 8mm (around 1/3in) long. They feed on the leaves from mid-spring to mid-summer.
Overwintering eggs hatch in spring and the larvae immediately start feeding on the newly emerging leaves. By late spring/early summer, the larvae are fully grown and then move into the soil to pupate. The adult beetles emerge in summer and, after mating, the females lay eggs on the woody stems of viburnum plants, which overwinter there.
What do they affect?
Viburnums, but particularly:
- Viburnum tinus
- Viburnum opulus
- Viburnum lantana
What do they do?
The larvae do most of the damage, during spring and summer. They remove most of the leaf area between the main veins and produce a “lace doily” effect. The adult beetles also feed on the leaves, but the damage is much less extensive than that caused by the larvae.
Heavy attacks, especially on Viburnum tinus, can result in most of the foliage being severely damaged. And, being evergreen, damaged Viburnum tinus look unsightly for several years.
The eaten leaves also become discoloured with brown, dried-up edges to the holes and all over the leaves.
How to control viburnum beetles
Timing is essential in the control of viburnum beetle, as the larvae need to be controlled before they cause extensive damage. Check viburnum plants regularly from early spring to catch the newly emerging larvae.
Squash the larvae or remove them and the leaves they’re feeding on as soon as you see them.
Careful hoeing around the plants, so as not to cause any damage to the roots, may kill the pupae, or expose them to foraging birds and other animals.
It may be worth pruning out branches of badly attacked Viburnum tinus, since this foliage can remain for several years. Although deciduous viburnums also look unsightly, their leaves will drop in autumn.
There are numerous chemical insecticides available that will kill soft-bodied insect pests, such as viburnum beetle larvae. Just bear in mind that the majority of these are what is known as “contact” insecticides. That is, you have to spray the actual insect (make contact with it) to kill it. If you miss some, these will not be affected. Also, most are based on “organic” or “naturally-occurring” materials and have very little persistence once sprayed on to the plant.
A systemic insecticide (BugClear Ultra) – which also kills on contact – is absorbed by the leaves and moves all around inside the plant, so can kill the larvae and adults as soon as they start to eat the foliage.
The correct timing of spraying is essential to kill the larvae, and especially before they cause extensive damage. Spray when the newly hatched larvae are feeding in mid-April to early May. Later sprayings can be used to kill the adult beetles – timing the spray before the adults mate and the females lay their eggs.
Use plant protection products safely. Always read the label and product information before use. Plants in flower should not be sprayed due to the danger to pollinating insects. Either spray early in the morning or late in the evening when pollinating insects are less likely to be active.
There is nothing you can do to prevent viburnum beetle attacking your viburnums.