Box Blight: How to Spot It, Treat It and Keep Your Box Healthy

Box (Buxus) has been a favourite in British gardens for generations. From neat low hedges around borders to topiary balls and clipped shapes, it’s hard to beat for providing year-round structure.

Unfortunately, box has also become associated with a couple of increasingly common problems – particularly box blight and box tree caterpillar.

If your box is turning brown, losing its leaves or simply looking rather sorry for itself, don’t give up on it immediately. Identifying what’s causing the problem is the first step, and there are things you can do to help.

What is box blight?

Box blight is a fungal disease affecting box plants.

It particularly likes warm, damp and humid conditions. Densely clipped box can provide an ideal environment because moisture remains trapped amongst the foliage and there is relatively little air movement.

The disease can be spread by infected plants and leaves, splashing water and contaminated tools, so good garden hygiene plays an important part in controlling it.

How can I tell if my box has blight?

There are a few characteristic symptoms to look for.

You may first notice brown or dark spots on the leaves, which can develop into larger brown areas. Leaves then begin to fall, sometimes quite rapidly, leaving bare sections of the plant.

Take a close look at the stems as well. Dark or black streaks on younger stems can be another indication of box blight.

If a previously healthy box suddenly develops brown patches accompanied by significant leaf loss, box blight should certainly be considered.

Is it box blight or box tree caterpillar?

This is an important distinction because they’re two completely different problems.

Box blight is a fungal disease. Box tree caterpillar is a pest that eats the plant.

Box tree caterpillars can strip large quantities of foliage and leave a plant looking brown and bare, which means the damage is sometimes mistaken for blight.

Look closely at the affected plant. If you find caterpillars, webbing or obviously chewed leaves, you’re more likely to be dealing with box tree caterpillar.

With box blight, you’re more likely to see leaf spotting, leaf fall and dark streaks on the stems.

Buxus being used in a formal garden

What should I do if I find box blight?

Don’t automatically assume the whole plant needs to be dug up.

If the problem is reasonably localised, start by dealing with the affected areas. Remove badly infected growth and collect the cuttings rather than allowing them to fall beneath the plant.

It’s also important to clear away fallen box leaves from underneath and around the plant. Infected material left on the ground can contribute to further outbreaks.

Don’t put obviously infected box material on your home compost heap.

After working on an affected plant, clean your secateurs, shears and other tools before moving on to another box plant.

Can box blight be treated?

Yes. A suitable fungicide can be used as part of a box blight management programme alongside good garden hygiene.

At Chard Plant & Garden Centre we stock Provanto Fungus Fighter Plus, which can be used against box blight when applied according to the manufacturer’s instructions.

Fungicide shouldn’t be regarded as a substitute for dealing with the conditions that encourage the disease. Removing affected material, clearing fallen leaves and improving airflow around the plant remain important.

When using any plant protection product, always read the label and follow the instructions on the pack, including application rates, intervals and the maximum number of treatments.

If you’re unsure which product you need, ask us and we’ll point you in the right direction.

Give your box some breathing room

One of the simplest ways to make conditions less favourable for box blight is to improve airflow.

Box is traditionally clipped into very dense shapes. It looks wonderful, but tightly packed foliage can stay damp for considerably longer after rain.

When pruning, consider opening the plant slightly rather than continually creating an extremely dense outer surface.

It’s also best to avoid clipping box in wet weather.

Water the roots, not the leaves

How you water your box matters too.

Instead of spraying water across the entire plant, aim the water directly at the soil around the roots.

A watering can is particularly useful because it gives you much greater control over where the water goes. You’re watering the plant rather than unnecessarily soaking all of its foliage.

If watering is necessary, doing it earlier in the day also gives any accidentally wetted foliage more opportunity to dry.

Keep your box healthy

Don’t forget the basics.

During prolonged dry weather, established box can still become drought stressed. Water thoroughly when necessary rather than giving plants frequent small

amounts of water.

Applying a mulch around the root area can help retain moisture and reduce competition from weeds. Keep the mulch slightly away from the main stems.

Feeding can help maintain healthy growth, but avoid the temptation to overfeed. Too much nitrogen can encourage large amounts of soft new growth.

Buxus showing new growth

Be careful not to spread it around the garden

If you have several box plants, start with those that appear healthy and leave any suspicious plants until last.

Clean your tools before moving between affected and unaffected plants.

It’s also worth remembering that infected leaves can stick to gloves, boots and equipment, so good hygiene isn’t just about your secateurs.

What if box blight keeps coming back?

Sometimes, despite your best efforts, a particular box hedge or plant suffers repeated outbreaks.

If a plant is severely affected year after year, replacing it may eventually be the most practical option.

That doesn’t mean abandoning the clipped evergreen look.

Japanese holly (Ilex crenata) is one of the best-known alternatives to box and can be clipped into hedges and shapes. Lonicera nitida is another possibility, and there are other compact evergreen plants that can provide structure depending on the position and the effect you’re trying to achieve.

Prevention is better than cure

There’s no single magic solution to box blight.

The best results come from combining several simple measures:

• Keep an eye out for the early signs.

• Remove badly affected growth.

• Clear fallen leaves from underneath plants.

• Keep pruning equipment clean.

• Encourage good airflow.

• Avoid unnecessarily wetting the foliage.

• Water at soil level.

• Use an appropriate fungicide where necessary, following the label instructions.

Most importantly, don’t assume a brown box plant is a dead box plant. Work out what’s causing the damage before deciding what to do.

Make sure all of your infected plant parts are removed.

Not sure what’s wrong with your box?

If you can’t decide whether you’re looking at box blight, box tree caterpillar or something else entirely, take a few clear photographs of the plant.

Try to include a picture of the whole plant as well as close-ups of the affected leaves and stems, then bring them with you when you visit us.

We’ll do our best to help identify what’s going on and advise you on the next step.

Chard Plant & Garden CentreHelping you get the best from your garden.