Box blight (Cylindrocladium buxicola) is a fungal disease that affects box (Buxus) plants. It first appeared in Britain in 1998 and is worst in warm, humid conditions. Box blight causes leaf browning and stem dieback. Box hedges develop unsightly straw-coloured bare patches, which are especially noticeable on box topiary and parterres. Box blight doesn’t kill the roots, but it does weaken the plants. Recovery is possible, but it takes perseverance to keep the problem under control – this is easier if you catch it early.
What is box blight?
Box blight is a disease that affects the leaves and stems of Buxus. It’s caused by the fungus Cylindrocladium buxicola (syn. Calonectria pseudonaviculata).
There’s another type of blight that affects box – Volutella blight – but this does less damage to plants and is easier to control.
Identifying box blight in your garden
Box blight can be confused with the symptoms of box tree caterpillar, so examine your plants closely for the following symptoms:
- Dark lesions on leaves, which turn brown and fall, leaving bare stems
- Black streaks and dieback on young stems
- White spores on the undersides of infected leaves
The symptoms of Volutella blight are similar to box blight, but there is no black streaking and you may notice pink spores on the undersides of the leaves.
Find out how to identify box blight and prevent its spread, in this clip from Gardeners’ World:
Controlling box blight
If you notice box blight, take prompt action to save your plants as it’s difficult to treat once it’s taken hold. You may want to prioritise your most cherished plants, as controlling box blight can be labour intensive.
Option 1 – cut out infected areas
As soon as you spot signs of infection, cut out the infected area, plus a generous area around it – the infection has probably progressed further than initially appears. Do this in dry weather – cutting back in wet conditions will risk spreading the disease. If you are not an organic gardener, you may help to contain the spread of the fungus by applying a fungicide before and after cutting back infected plants.
Make sure you practise good hygiene:
- Ensure your pruning tools are sharp and disinfected every time you use them – avoid using power tools as these can crush leaves, making them more prone to infection
- Bin infected material to stop blight spreading around the garden – don’t add the prunings to your compost bin
- Clear away as many fallen leaves from around the plants as possible – placing a plastic sheet around the plant, or using a garden vac makes this easier
- Clean hands, pruning tools, clothing and shoes to stop spreading the disease around the garden
Option 2 – cut back plants by half, or cut them right back
If cutting out infected areas has not got on top of the problem, you may need to take more drastic action.
You could try cutting the height and width of your plants back by half or a third. This of course is not an option on topiary but is worth trying on hedges. This removes the affected areas and gives more light and air circulation to the healthy parts of the plant lower down, promoting their recovery.
You could also choose to cut plants right back to stumps, or completely remove a badly affected plant.
In this video, Monty Don takes action to rescue his diseased box hedging. He cuts out the blight-affected growth, explaining how and where to cut, and why this should help to save diseased box plants. Afterwards, he shows you how to clean your tools and what to do with your clippings to avoid spreading the blight spores to other unaffected box plants:
Water, then feed plants that have been cut back with a general purpose fertiliser (such as fish, blood and bone or seaweed feed). This should encourage the plant to produce new, healthy growth.
Preventing box blight
Check plants regularly for signs of infection
It’s much easier to treat box blight if it’s caught early.
Prune only once a year, in dry weather
This will mean plants are less dense, with better air circulation within their foliage. Pruning once a year also reduces the risk of spreading infection. Only prune in dry, breezy weather. Trim early in the season so there’s plenty of time for growth to ‘ripen’, reducing the risk of frost damage that will allow fungus spores to enter.
Ensure good air circulation around your plants
Make sure the area immediately around your plants is free of other plants, to improve air circulation around them. Avoid planting in dark, damp areas – choose an open, bright spot.
Practise good hygiene
Be scrupulous in removing fallen leaves from around your plants (a garden vac is very useful), and disinfect pruning tools between plants.
Apply a plant tonic
Organic products are available that as as tonics, keep plants healthy and discouraging outbreaks, but they need to be applied regularly throughout the growing season, from April to October.
Avoid splashing the leaves when watering
Only water around the base of the plant, as box blight thrives in humid conditions.
Avoid high-nitrogen fertilisers
These cause soft, sappy growth that is more prone to infection. Blood, fish and bone or seaweed feed are good all-purpose organic feeds that can be applied once a year in spring.
Buy from a reputable hedging supplier
Buy from a supplier that propagates from their own healthy plants. Quarantine plants for at least a month before planting out, to check that they are free of blight.
Try growing a resistant variety
The variety ‘Faulkner’ is said to be the most resistant to box blight.
Don’t replant for six years after an infection
If you have had box blight in your garden previously, wait at least six years before replanting box, as the spores can linger.
Alternatives to box
If you have lost plants to box blight (or box tree caterpillar) or are unwilling to plant more due to potential problems, there are plenty of alternatives to box.
Some, such as box leafed holly (Ilex crenata) or Lonicera nitida look similar to box and can be grown and clipped in the same way. Yew is a great alternative for hedging and topiary. While other plants are not direct replacements, some have the added advantage of flowers that are attractive to pollinators (such as lavender, Mexican orange blossom and podocarpus), while others have attractive variegated foliage (Euonymus fortunei or Euonymus japonicus). Some, such as berberis, have fiery autumn foliage.
Read more about our recommended alternatives to box.