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.