Viburnum beetle

What you are looking at

A viburnum with its leaves eaten down to a network of veins, so the whole shrub looks like green lace held up to the light. On a laurustinus hedge it can be every leaf on the outer face.

In spring, turn a damaged leaf over. Creamy yellow grubs marked with black spots and dashes feed in groups on the underside, from April into June, and they are what does the first round of damage.

They then drop into the soil to pupate, and from July the adults emerge, small greyish-brown beetles about 5 mm long, and start on what is left. So the shrub gets stripped twice in one season by the same insect wearing two different shapes.

The eggs are on the shrub all winter

The part that turns this from an annoyance into something you can deal with sits on the shrub all winter, in plain sight.

In late summer, the females chew rows of small pits into the underside of the current year’s shoot tips, lay their eggs inside them, and cap each pit with a crust of chewed wood and excrement. Those caps sit there, dark and slightly raised, in neat lines along the young wood, from September right through to March.

They are visible. Turn a shoot tip over in January and you can see them.

Cut those tips out over the winter, burn or bin them, and the larvae that would have hatched in April never appear. One session with the secateurs on a still afternoon, on a shrub that has nothing else going on, does more than a summer of picking grubs off leaves.

What it does and does not kill

A single defoliation is survivable. Viburnum breaks again, and a shrub in good heart replaces the leaves within weeks.

What kills is the repetition. Two strippings a year, several years running, on a shrub that is not watered or fed, thins the plant out, kills back the outer growth, and eventually finishes it. A great many laurustinus hedges have gone this way in southern England.

Keeping the plant well fed and mulched is therefore a control measure rather than an afterthought, because it buys the shrub the reserves to keep replacing what it loses.

What to do about it

Turn the shoot tips over between October and March, find the rows of capped pits, and prune those tips out.

Check the leaf undersides weekly from April and pick the larvae off, or take off the leaves they are grouped on.

Look again from July, when the adults start.

Mulch, water and feed the shrub so it can afford to refoliate.

Where a hedge has been stripped several years running, replant with a viburnum the beetle largely ignores, such as V. x bodnantense, V. plicatum or V. x burkwoodii.

Leave the birds and the predatory bugs to help, and keep sprays off the shrub.

What it gets mistaken for

Caterpillars and sawfly larvae both have fleshy prolegs along the abdomen behind the three pairs of true legs. Viburnum beetle larvae have none, which settles it in a couple of seconds.

Box tree caterpillar leaves silk, frass and stripped box, and touches nothing else.

Vine weevil adults cut small clean notches out of the leaf margins at night and leave the rest of the leaf whole.

Viburnum whitefly leaves small black scale-like young on the leaf undersides and sticky honeydew, without eating any tissue.

Powdery mildew and leaf spots discolour a viburnum leaf without removing any of it.