Battling beetles

Susan Main, Horticulturist at RHS Garden Harlow Carr

Rays of autumn sunshine set aflame the shining red berries of the glorious guelder rose - or viburnum opulus - a real beauty of our native hedgerows.

The fragrant white flowers are held in a flat-topped cluster or corymb, reminiscent of their relative the elderflower. These attract insects such as hoverflies and the berries too are a boon for wildlife, providing a food source for birds and small mammals, although they are said to be poisonous to humans.

Undeniably versatile, the viburnum genus contains a specimen for every garden and every season, from beautiful foliage to fragrant flowers and bountiful berries. They are adaptable for many situations in the garden, from hedges to wildlife gardens and individual specimen planting to mixed borders. They are tolerant of most soil types, managing well with dappled shade, although full sun provides the best display.

Which to choose:

Viburnum farreri and V. bodnantense ‘Dawn’ are decorative specimen plants that carry beautiful fragrance across the garden, flowering in late winter to early spring.

Viburnum tinus ‘Eve Price’ is a compact shrub offering pink flower buds opening to white and followed by blueish berries suitable for a container.

Viburnum davidii, with its glossy deep-veined leaves, is very tolerant of dry shade conditions. We have utilised this plant in a number of situations across the garden at RHS Harlow Carr, specifically with this advantage in mind to manage sites often seen as difficult to plant.

Care and Maintenance In general, most viburnums require little pruning and this is best done before the start of the main growing season in late winter or early spring. Viburnum tinus can be lightly clipped to maintain its shape and winter flowering viburnums can have some older, less productive stems removed to the base, allowing new growth to thrive (only remove up to a third of stems).

Pests and diseases There are few pests of viburnum, however, I for one can vouch for the destructive power of the viburnum beetle, having gone to great lengths to attempt to halt its devastating appetite for defoliation. Within an area of Harlow Carr known as the Foliage garden, the greedy gobblers created lace curtains of the foliage of the viburnum opulus ‘Aureum’!!

My research to identify a method of control landed upon the helpful advice of ‘select a less susceptible species’, the species of opulus and tinus being most susceptible.

I decided to tackle the problem based around the life cycle of this pest. The female beetles chew into stems and bark to lay their eggs which are sheltered over winter. In spring the hatching larvae begin the process of leaf damage before burrowing into the soil around the plant to pupate. The newly-emerged adults continue the defoliation through the summer. The progress of the infestation becomes worse as the females target more and more of the dying stems in which to lay their eggs. Apparently this can lead to the loss of the plant within a relatively short number of years.

I had previously tried removing only affected stems which had died back, however, during this year the damage became so devastating that I decided to hard prune the entire plant. I removed all stems for disposal away from the compost heap in the hope that any remaining eggs and adults would be destroyed. As new growth has emerged I have been vigilant to hand pick any adult beetles. The growth is now coming back well, but only time will tell next year as to how successful my efforts have been. Here’s hoping!

Jobs for the Week

* Empty compost bins and use for mulching or as a soil improver, as well as adding nutrients this will condition the soil for better aeration and drainage.

* October is a good time for planting or moving trees and shrubs as the soil is still warm enough for plants to settle in before winter.

* If you haven’t yet planted garlic and your soil is too wet to do it now, then try grow individual cloves on in a modular tray; they can then be planted out in early spring.

With thanks to Susan Main, Horticulturist at RHS Garden Harlow Carr

DIARY DATES

Saturday 15 – Sunday 16 October: Alpine Weekend The Alpine Weekend will showcase the very best of these hardy plants in association with the Alpine Garden Society. Pick up interesting varieties and get advice from a host of UK alpine plant growers. On Saturday, enjoy an Alpine Garden Society show. On Sunday, the West Yorkshire group will be competing for the best locally grown alpines. Normal garden admission.

22 – 30 October: October Half Term – Animals of the Night Our October half term fun will focus on creatures that come out at night – from bats and badgers to hedgehogs and owls. See pygmy hedgehogs up close, enjoy a daily wildlife trail, book a place on the holiday club and make your own pumpkin seed hedgehog. Normal garden admission except holiday club places. Buy garden tickets online & save 10%.

29 October – 2 November: The Apple Display Feast your eyes on fantastic apple displays bursting with flavour and colour, enjoy a taster or two and get free advice on growing your own from The Northern Fruit Group. Members of the group will be on hand on 29 & 30 October to identify apples from your own garden. Normal garden admission. Buy garden tickets online & save 10%.