Box blight or box caterpillar: have you got these problems? What to do about buxus diseases

Is there anyone who hasn't yet been affected by Box Blight or any other problems resulting in Buxus becoming sick? You don't have to look very far or particularly hard before noticing that the fungal diseases spreading around Buxus sempervirens is showing no signs of abating. In fact it's unusual to see box that hasn't been attacked by die-back or yellowing, especially topiary pieces and parterres. So what can be done about these devastating problems?

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Buxus sempervirens has small-leafed evergreen foliage and responds well to clipping. However, it is being decimated by disease. The blight is caused by different types of fungi. Cylindrocladium buxicola and Pseudonectria buxi/Volutella buxi often appear together on plants which include not only Buxus species but other plants within the same family (Buxaceae).

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It can be seen on the undersides of leaves. What's more, there's the nifty little box tree caterpillar causing munching havoc too. Not to mention a soil-borne disease called Phytophthora root rot which sometimes causes box to fail unexpectedly. Then there's box rust, box sucker, the leaf-mining gall midge, mussel scale and the box red spider mite problem.  It does seem that good fortune is not favouring the humble Buxus.

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The box tree caterpillar is a nibbling pest that loves to eat Buxus.

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Box tree leaf miners leave tell-tale holes and marks on the foliage But how do you know what disease your box is suffering from and what should you do about it? Firstly, be informed and aware. The greater your knowledge, the more chance you have of overcoming the problem. Box blight of some sort of another can attack everywhere and has no respect for status. Your garden box can occupy a plot belonging to a stately home; a patch outside a London suburb or occupy pride of place on a humble high-rise balcony. The problem crosses all boundaries. ‍

Signs to look out for include the browning and falling of foliage which results in bare patches. Young stems can suffer from die-back. You might even see spores on the undersides of infected leaves. These are white spores for C. buxicola and pink spores for P. buxi, shown below.

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Nobody wants to see Box Blight spores. Check your foliage to see what's appearing.

Firstly, disease prevention. The most important thing you can do is to isolate any new stock of box that you buy in. Keep it apart from others for at least three weeks to make sure there's no infection. The next thing to consider is the frequency and timing of clipping. More frequent clipping can exacerbate the risk because not only are you bruising the foliage but the act of topiary means the plant is naturally denser and thicker. Free-flowing air around the plants can help to keep problems at bay. Try not to clip on humid or wet days.

Water your box plants from below rather than sprinkling moisture over the foliage.

Next, try to avoid soaking the foliage unnecessarily. Many types of fungus like humidity and it stands to reason that if there’s a problem it will spread faster in warm, damp environments. Box is actually a drought-tolerant plant and prefers to be kept dry. What can you do about the problem? Firstly, cut off the affected parts and destroy them. Bear in mind that fungal spores can linger on and in the soil for many years so you might want to consider removing the top layer. Next, feed your plant; keep the foliage dry; avoid unnecessary clipping and ensure the air can flow freely around it. Other problems can be relatively easily dealt with. If your box has been affected by a box sucker invasion, for example, the leaves will be curled around little green sucking insects. ‍

Box suckers result in the leaves curling around the little insects. You can cut off this foliage but be sure to destroy it. In this case, just clip off the affected part and ensure to destroy the clippings.

If you find fine webbing on your plants and see that some of the foliage has been nibbled, you might have box caterpillar. These gradually change into box tree moths which have white wings with brown borders. You might also see yellow, flat eggs on undersides of foliage. Remove as much and as many of these by hand. Clip off affected foliage and destroy. You can also set a pheromone trap to catch the adult moths.

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For red spider mite, mussel scale, and box gall mite, there are chemicals that are effective, should you wish to try them. Removing the affected parts is always a good idea.

Because there is currently no effective cure for box blight, experimentation could well be the way forward. Many people say that by feeding and nurturing they are able to save their plants. This can take several years. Biological control is also another option.

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Beautiful topiary, similar to the swan above, or parterres in formal gardens, all rely on healthy evergreen plants!

Are there alternatives to Box?

Other plants can be substituted for the stricken Buxus. If you want low hedging and topiary there are many different options, each with their own merit. You can still make a statement with topiary and clipped hedging. It doesn't have to be box! 

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• Top of the popularity stakes is taxus baccata (yew) which has many lovely properties and responds well to clipping. It's beautiful too, with its dark green evergreen, linear foliage and red berries, all of which are poisonous. Levens Hall in Cumbria (below) is a very famous topiary garden that uses a lot of yew.

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• Then there are various cultivars of Euonymus fortunei which can be formed into balls and shapes. These have interesting evergreen foliage including creamy, gold and variegated.

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• What about Ilex crenata, which is remarkably box-like? This is a species of holly which hails from China and Japan. It's evergreen and can be clipped into various forms. It is particularly loved as a cloud-pruned architectural feature (see picture below) and so far has remained unaffected by the diseases that are decimating Buxus.

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• Consider Osmanthus delavayi (pictured below) for its glossy dark green leaves with finely serrated edges. What's more, this charming shrub has masses of scented, jasmine-like flowers in mid to late spring.

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• There are several forms of Berberis which could be useful because they have small leaves and they respond well to pruning. Look out for the thorns but don't be alarmed by the colourful sap. Historically it was used as a yellow dye.

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• How about Hebe such as Boughton Dome (below)? This, and many other types of Hebe, forms a natural dome-shape and is relatively trouble free.

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• Lonicera nitida (pictured below) is a shrubby honeysuckle that responds well to clipping. It's more vigorous than box and will need shaping at least twice per year, but very useful as a structural form.

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• Rosemary (pictured below) is highly successful as a clipped form. It can be shaped into larger hedges (clip twice per year) and even be used as a bonsai tree. But it probably isn't suitable for low parterre hedging as it looks at its best at a height of around 60-120cm.

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• Even lavender (see below) can be used to form mounds and hedges, but care needs to be taken not to cut back into old wood as it rarely regrows from this treatment.

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It's easy to see that there are several alternatives to Buxus sempervirens. All that's required is a little thinking 'out of the box'. Enjoy being creative!