PlantAdvice.co.uk

Each year the charity’s entomologists add up all the enquiries they have answered and produce a list of the ten most troublesome pests. In most years slugs and snails have topped this list but in 2010 RHS members wanted to know more about problems associated with the viburnum beetle.

This pest eats the foliage of various viburnums commonly grown in gardens, especially the evergreen shrub Viburnum tinus and the deciduous Viburnum opulus, also known as guelder rose or snowball bush. Adult beetles cause some damage in late summer but it is the grub stage in April-May that can cause severe defoliation.

Principal RHS Entomologist, Andrew Halstead says:

‘’Viburnum beetles are in our top ten list most years but they do seem to have become more troublesome over the last decade. The damage to evergreen viburnums is more apparent because it can be seen all year round.’’

Enquiries into two sap-sucking insects, cushion scale and horse chestnut scale, have increased. Cushion scale infests the underside of leaves on evergreen shrubs, such as camellia, rhododendron, holly and Trachelospermum. Horse chestnut scale is seen on the trunks of horse chestnut, lime, bay trees, sycamore and maples.

RHS members were also concerned about the glasshouse red spider mite, which sucks sap from a wide range of greenhouse and garden plants. Andrew says ’’The relatively hot dry summer last year meant that red spider mite become more of a problem on outdoor plants. However, a benefit of the dry weather was that it also restricted the activities of slugs and snails which prefer wet, cool weather.’’

The number one plant in terms of pest enquiries in 2010 was grass. This was followed by viburnums, roses, apples, fuchsias, lilies, plums, maple, pears and bay. Lawns are usually the number one problem because they have a wide range of pest problems, although most of the damage is caused by chafer grubs.