“Sharing the best in gardening,” the masthead of the Royal Horticultural Society (RHS) proclaims.
I wonder if ‘sharing the worst in gardening’ might also be included, unspoken, for Cydalima perspectalis is, most assuredly, not the best thing a gardener could wish for; yet what follows is largely taken form the RHS website on this problem. Cydalima perspectalis is the scientific name for the box tree moth; and, while the actual moth is not a problem for gardeners, its caterpillars certainly are.
Now, before we look at what the RHS has to say about these caterpillars, this comes from Wikipedia. “Cydalima perspectalis or the box tree moth is a species of moth of the family Crambidae. It is native to eastern Asia (Japan, China, Taiwan, Korea, the Russian Far East and India). It is an introduced species in Europe, first recorded in Germany in 2006, and subsequently in Switzerland and the Netherlands in 2007, Great Britain in 2008, France and Austria in 2009, Hungary in 2011, Romania and Turkey. It is also known from Slovakia, Belgium and Croatia (and) in 2013 it was found new to Denmark at several sites.” You get the general idea. This is an alien species which, as is not uncommon with alien pests, has found Europe to its liking and has no natural enemies in this continent.
And so we go to the RHS. “By the end of 2014 the moth had become established in parts of London and surrounding counties; in many cases the caterpillars had caused severe defoliation indicating that the moth is likely to become a serious problem. The adult moth usually has white wings with a faintly iridescent brown border, although the wings can be completely brown. The moth has a wingspan of around 4cm … say, 1¼ inches in old money. Gardeners are likely to become aware of box tree caterpillar when they find webbing and caterpillars on box plants.” And why would a gardener have box plants? Well, this is taken from the website of s supplier of these plants in Farnham, Surrey. “Box hedging … Buxus sempervirens … has been used for a very long time to make small hedges and is ideal for formal borders as it will grow on most soils. A neatly cut box hedge looks very smart and usually needs clipping only once a year. Box hedging will grow equally well in dry acid soils and alkaline soils but it does not like waterlogged soils.”
Scottish gardeners grow box hedges. Any who aspire to embrace the art of topiary … … training plants (typically evergreen shrubs and trees) into intricate or stylized shapes and forms … most often use box, holly or yew to create their artistic plant statues. Box is right up there, probably number one in the topiarist’s list of favourite plants. Now look again at the address of the supplier whose website I have quoted. Farnham, Surrey … which is about thirty miles from London. Now I am not for one moment suggesting that this supplier of box plants has, or will, ever knowingly spread this pest. I am merely showing how extremely easy it is for an alien pest to be inadvertently transhipped to a previously unaffected area; after all, that’s exactly how Cydalima perspectalis made its way from the Far East to Germany and thence through Europe; and it may take only a few tiny eggs or a couple of caterpillars.
So what’s to look out for? The pale yellow flattish eggs are laid on the underside of box leaves, overlapping each other; the newly hatched caterpillars are greenish-yellow, with black heads; and older caterpillars reach up to 4cm … 1¼ in … and have a greenish/yellow body with thick black and thin white stripes. I don’t expect you to find any in Falkirk in the near future; but if you do, seek advice about Cydalima perspectalis on the RHS website.