Is it time to give up on box hedges?

Published date18 March 2023
As a long-time admirer of box hedging, I feel your pain. Despite the threat of various new pests and diseases in recent decades, this slow-growing, hardy evergreen shrub has been a mainstay of ornamental gardens around the world for centuries - just think of the formal gardens of Versailles - and remains unequalled in terms of its year-round good looks, versatility and ability to tolerate hard clipping and training

Native to Asia, but a relatively recent arrival in Ireland, the first recorded evidence of box moth (Cydalima persimilis) in Europe was in 2007, and the first recorded evidence of it in Ireland was in Dublin in 2018. A very destructive pest of box hedging and box topiary, its large lime-green and black caterpillars overwinter in weblike cocoons concealed within the plant before emerging in spring to feed voraciously on the foliage and stems.

These quickly become adult moths that fly off in search of nearby host box plants on which to lay their yellow eggs, and so the life cycle continues, with new colonies subsequently appearing in nearby gardens. Badly infested plants can potentially be completely defoliated within a few weeks, seriously weakening and eventually killing them.

Conventional insecticide controls are damaging to the environment and not terribly effective. But organically acceptable modern biological controls in the form of specific nematodes are very effective, just so long as their use is well timed. I say well-timed because the most important thing to remember about any form of nematode control is that it's not preventative. So, as strange as it sounds, it won't work unless the host pest in question is already present in sufficient numbers.

It's also important to point out that in an urban environment like yours, where you're closely surrounded by other gardens with box hedges or box topiary also potentially infested with box moth, complete eradication isn't realistically achievable.

Instead, the gloomy truth is that your plants remain at risk of being reinfected by moths visiting from other gardens. But you can do a huge...

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