Are we seeing the end of the traditional Box tree hedge?

I have always admired the precision of a tightly clipped box hedge or the art of some beautiful topiary. I have used low box hedging at home as an edging to protect perennials from my dog who has no respect for planting spaces. Over the years I have become an expert in propagating cuttings to create more and more hedging for free. I find the twice yearly clipping strangely therapeutic and the forming of new shapes a beautiful green art. The dense green backdrop of Box plants works brilliantly providing structure and form within a space that lasts all year and is quite invaluable to a design.

In recent years I have felt particularly lucky to have avoided box blight and managed to keep my box plants alive and free of problems. Whilst having renovations to our house last year, I carefully transplanted much of the box edging and managed to keep enough of it alive to transplant twelve months later into its new position.

What does a Box tree caterpillar infestation look like?

On returning from holiday I noticed some brown leaves and rather odd leafless stems on one of my box plants. On closer inspection I found the same defoliation in patches on another and then another. Parting the branches, I found the tell-tale webbing characteristic of a Box tree caterpillar (Cydalima perspectalis) and green pellets of excrement known as ‘frass’.

The caterpillars themselves were initially quite hard to see, often hiding in between two leaves and a shelter of webbing. Green and black striped with a black head they were easiest to spot when they moved. Many were inside the plant quite deep and twirled around stems or hidden between leaves. Only the largest caterpillars were easy to find and there were lots of them. The small ones I noticed almost by accident but made me realised that there were many stages of eggs and caterpillars on one plant.

Box tree moths themselves are quite small, here shown with a box leaf for size. They are also not found during the daytime so your probably wouldn't even know you had an infestation until damage was visible. Originating from south-east Asia, the moth was first found in Kent in 2008 and has since spread from the south-east across the UK.

I was surprised that I didn’t feel as angry or upset as I expected. I think I have been feeling for a while like my box was on borrowed time. However, I knew I needed to start doing some research and come up with a plan for what I was going to do. Potentially the loss of all the box plants in my garden going into autumn and winter was going to be quite noticeable.

How quickly will it act?

Box month can have several cycles in a season which lasts from March to October. The patches can start quite small which gives you a chance to act if you know what you are looking for. Once the caterpillars take hold, they can completely defoliate a box ball in a matter of about 10 days. Box can recover from an infestation, however, if the caterpillars also start to strip the bark of branches this is effectively girdling the stems and will cause them to die.

What can I do about it?

There are several different courses of action that can be followed to deal with a box tree moth infestation.

· Using a biological control containing the micro-organism Bacillus thuringiensis to spray the plants. Only effective when the temperature is above 15◦C when the caterpillars are eating as it has to be ingested for it to work. This treatment only lasts 10 days and breaks down under UV light so needs to be repeated several times to be effective.

· Using an insecticide to kill all the caterpillars. Potentially less effective than a biological control and also potentially killing other insects and beneficial pollinators. This treatment would need to be repeated at intervals to kill off any new caterpillars hatching.

· Picking the caterpillars off by hand. This would need to remove all caterpillars, pupae and webbing as well as the debris under plants to remove all traces of caterpillars, eggs, larvae and pupae.

· Using a hose to try to spray off the caterpillars. Not a good idea to spray off the caterpillars with a hose as this creates the perfect conditions for box blight to take hold. Any watering of box plants should always be done only at the base.

· Setting a pheromone trap to catch male moths and therefore reduce the number of fertilised eggs laid by females. These need to be placed where moths are likely to hide from sunlight. Traps last up to eight months, enough to cover a full box moth season.

· Applying nematodes, a biological treatment, where tiny worms enter the caterpillars disrupting their digestive system and kill them. Supplied as a powder these need to be sprayed via a hosepipe in specific conditions and repeated several times.

As this is an invasive species there are no natural predators for box moth in the UK. The caterpillars ingest the box leaves absorbing their toxins so our native birds have been reluctant to eat them. There is some evidence to suggest that some birds are getting a taste for them but at the moment they are not eating enough to seriously reduce the population. In my garden those I have picked off and left for birds to eat have been untouched.

Having looked at all the possible ways that I could deal with the infestation in my garden I confess I do not have the time of the interest in most of the above. I have tried picking off the caterpillars, almost impossible to get them all and quite disgusting. I don’t really want to spray with insecticide having worked hard to encourage wildlife and an array of insects into my garden I don’t want to risk killing them off. Biological controls seem the best option for me. But, the need for constant repetition not only this season but forever, is making me think that this is a battle that I just don’t really want to begin.

Am I fighting a losing battle?

It seems that the writing is on the wall for the box plant until a reliable treatment is developed that can continuously deter or kill the moths and caterpillars. Personally, I don’t want to be constantly picking off the caterpillars or spraying with chemicals that could potentially be killing off all the other insects that I have worked so hard to bring into my garden. It seems that my box is doomed.

Is it time to think outside the box?

As a designer I have been investigating other potential plants that could be used instead of Box since blight became an issue. I have not specified Buxus in any new scheme as I didn’t feel comfortable planting something that I suspected was likely to fall victim to one or other of these problems. And was unlikely to survive.

My research has established that there are several box alternatives, the many studies including one by the RHS at Wisley to test different small leafed evergreen plants and their growing conditions are very interesting. My research so far has identified the following possible alternatives depending on the need for the purpose of the plant as hedging or topiary and the aspect of the site.

Yew (Taxus baccata) seems to be the gardener’s favourite as it tolerates clipping and can be formed into topiary or a low hedge.

Japanese holly (Ilex crenata), looks most like box but has flowers in spring and fruits in autumn.

Mock privet (Phillyrea angustifolia), makes excellent topiary, however as part of the olive family it likes warm conditions so will not tolerate cold or shade.

Euonymus japonicus is compact evergreen with glossy leaves. Useful low hedging and tolerant of quite exposed positions. Its leaf is larger than box so not so easy to clip into shape.

Box honeysuckle (Lonicera nitada) has smaller leaves than box and can be clipped into shape although it grows faster than does so would need more work to keep it in shape.

Hedge germander (Teucrium x lucidrys), has a crinkly edged leaf and makes good low edging and is drought resistant although sends up spikes of pink flowers in summer.

Hebe ‘Green globe’ has a naturally round habit and is tolerant of full sun and partial shade. It prefers moist soil and could potentially work well as a replacement to a box ball.

Wire bush, (Corokia), a native of New Zealand and a popular hedging plant which can be clipped into different shapes.

Pittosporum tobira ‘Nanum’, a much brighter green than box but will tolerate being clipped into shape and is one of the smallest pittosporum plants. It will need protection from cold or on exposed sites.

Is there another way?

In my garden where I have used Box as a low edging plant, I don’t really have time for something new to grow as I need to replace that barrier with another. To create a crisp edge, I am planning to use a willow or hazel hurdle to create the same kind of effect. The advantage that gives me in my space is that it will be a similar height to the box that I am going to have to remove, but thinner so that I will have more space for perennials.

I do like the structure that box provides within a border. Could there be another way for me to provide some of this structure within a domestic setting? There is a possibility of using some sculpture or pieces of art at strategic points to add structure.

We might be seeing the end of the Box tree in English gardens. However, gardens are ever changing and as one thing diminishes it just makes space to try something new. Although I am sad at what appears to be the end of an English tradition, I am also excited by the possibilities and will not mourn the loss of something which is no longer viable.