Life

The Casual Gardener: Bad news for box

Box is treasured for hedges, parterres and topiary but a combination of pests and diseases could undermine its popularity, writes John Manley

Caterpillar of the box tree moth – Cydalima perspectalis
Caterpillar of the box tree moth – Cydalima perspectalis Caterpillar of the box tree moth – Cydalima perspectalis

IF ONLY gardening were the proverbial 'bed of roses', where things always went according to plan and reality continually met our expectations. Unfortunately, our gardens’ heavy reliance on nature means they are sometimes vulnerable to its vagaries.

As I’ve preached on these pages for the past decade or more, the healthier the ecology of your garden and the greater its biodiversity, the less you need worry about sudden infestations or plagues of insects. However, no matter how many nettles and natural predators you have or how closely you adhere to a crop rotation system in the veg patch, your garden is never completely free of pests and diseases.

And last year, it seems, was particularly bad due to record temperatures and rainfall, according to the Royal Horticultural Society (RHS), who compile and monitor data on plant pests and diseases. The RHS head of plant health, Gerard Clover, and the society’s gardening advice team operate by the maxim 'a problem shared is a problem halved'.

"Dealing with pests and diseases is a daily reality for gardeners but by sharing their observations, insights and samples with RHS scientists they are helping us identify those areas where we need to focus our research efforts to better control pests and diseases," says Gerard.

What the RHS found last year was that for the first time in almost a decade, slugs and snails did not top their list of garden pests, based on the number of enquiries received by the society’s gardening advice team.

The title of top pest 2015 went to the box tree caterpillar, a native of East Asia, who was first spotted in Britain in 2011. A voracious feeder of box (Buxus), the larvae of the box tree moth are 4cm long and feed on the leaves of the host box plant under a blanket of pale fine webbing which can cover infected plants.

Before you panic, however, I believe this particular pest’s prominence in the RHS's list of notorious garden nuisances in many ways reflects the society’s prevalence in the south east England where the box tree caterpillar is now commonplace. I have been reliably informed by the Agrifood and Biosciences Institute in Belfast that this pest has yet to be spotted in the Occupied Six – or anywhere in (‘fortress’) Ireland it seems.

Slugs and snails came a close second in the RHS's premier pests league, with complaints focusing on spring and autumn damage – exacerbated by damp spells – to potato tubers, hostas, daffodils and all sorts of seedlings.

While the threat from the box tree caterpillar on this side of the Irish Sea may not be immediate, this hedging favourite may not as easily escape the second most reported plant disease, box blight. Pipped for first by the ever-popular honey fungus, box blight is caused by the fungus Cylindrocladium and is the scourge of hedges, parterres and topiary.

According to the RHS, the disease poses a serious threat Britain’s horticultural heritage, as box plants provide the structure of many historic formal English gardens.

Not yet as prevalent in Ireland as in Britain, box blight may still pose a threat the further south you travel. The symptoms include dark brown patches on the foliage with greyish fungal growth on the underside of the leaves.

It eventually causes die-back. High temperatures and rainfall over the spring saw a spike in enquiries to the RHS about box blight, as environmental factors combined to create the perfect condition for the disease to thrive.

The unusually warm wet weather in December saw an unexpected increase in enquiries at a time when the expected cold weather would suppress the disease.