Boxing clever Explore Michelle Murray’s proactive approach at the Trinity College Botanic Garden (TCBG) as she confronts the challenge posed by the box-tree moth caterpillar Neatly trimmed ribbons of Buxus sempervirens , common box, have become a staple in the well-ordered contemporary garden. Lining gravel driveways and perennial borders, this versatile, easy-to-grow and widely available plant provides year-round structure to the least considered garden style. So much so that the low box hedge has become a staple of urban garden design in some quarters. Despite its appeal however, box cultivation is not without its problems. It can suffer the dreaded box blight, which is caused by two related fungal pathogens. Appearing first as brown lesions on leaves, it usually goes unnoticed until the leaves have fallen leaving bare patches, latent fungal spores, and a distressed gardener! But it is a blight of a different kind which is currently sweeping through Dublin gardens where box is indeed common. It is not a fungus but an arthropod: the caterpillar of the box-tree moth, Cydalima perspectalis . If numbers are high, this beauty can methodically devour an entire box hedge or prized topiary, reducing it to bare skeleton in one season. The box-tree moth is an invasive species native to Japan, Korea and China, but has migrated across Europe devastating swathes of native wild and cultivated Buxus . It reached Britain in 2011 and is now widely distributed across all but the most northerly parts. It was first recorded in Ireland in Waterford in 2017, but it wasn’t until bare patches and the caterpillars’ characteristic webbing were spotted that its presence in Trinity Botanic Gardens was detected last year. As populations had become established however, by then it was too late to save one section of hedge. What to look for: Leaves bound or clumped together by tight webbing - peeling apart the leaves will reveal the cocoon or emerging caterpillar (pictured). Mature caterpillars – bright yellow/green, up to 4cm, with black stripes and spots and large black eyes What to do: As they have no natural predator in Ireland, and birds don’t eat them in sufficient number to reduce populations: Check box plants carefully and regularly from March If not too heavily infested, pinch out shoots with cocoons and pick off active caterpillars Try pheromone traps from April to August to trap male moths – this won’t kill them, but will indicate populations, however, as the caterpillars can overwinter in milder areas, pheromone traps are unlikely to be useful Biocontrol such as nematodes – caution: while marketed as ecologically safe, always use judiciously, if at all, as our understanding of their complex interactions with the ecosystem remains limited What to plant instead: Yew ( Taxus baccata ) Japanese holly ( Ilex crenata ) Box-leaved honeysuckle ( Lonicera pileata ) For warmer gardens: False Olive/Mock Privet ( Phillyrea angustifolia ) - ideal for coastal locations Pittosporum tenuifolium – try the dwarf varieties of ‘Tom Thumb’ (dark chocolatey purple) or ‘Irene Paterson’. Alternative approach For a new garden or replacement hedge, rather than monoculture, try cultivating a mixed planting. As well as looking interesting this will help to reduce the threat and spread of certain pests and diseases and will improve overall biodiversity. For larger hedges, mixed shrub border or specimen shrub or small tree, our beautiful native species can rival any exotic species. Consider the hawthorn ( Crataegus monogyna ) for April-May blossom, spindle bush ( Euonymus europaeus ) with its unusual pink fruits and striking autumn colour; guelder rose ( Viburnum opulus ), a pretty alternative to Hydrangea with jewel-like berries in autumn; alder buckthorn ( Frangula alnus ) with black berries; dog rose ( Rosa canina ); and for a specimen shrub or small tree, the strawberry tree ( Arbutus unedo ) with strawberry-like fruits or red-berried rowan ( Sorbus aucuparia ) are suitable for even a relatively small garden. All will attract beneficial insect and natural predator populations. At TCBG we plan to replace the traditional low box hedging with a native conservation hedge.
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