Horticulture Magazine

How To Identify And Treat Box Blight

a partially infected box hedge with varying colouration

Box blight is a fungal disease that can pose major problems for gardeners with box hedges.

In this article, we will look into this problem, and talk about what you can do to deal with this issue in an organic garden.

What Is Box Blight?

buxus shrub that has turned fully brown as a result of blight

Box blight is a fungal infection which impacts Buxus, or box hedges or topiary.

Two genetic types of a fungus called Cylindrocladium buxicola are responsible for this problem. [source]

In an organic garden, you will obviously avoid the use of synthetic fungicides, but in any case, fungicides alone are rarely able to cure the problem. [source]

Box blight can be a serious problem, and it is important to remain vigilant.

The sooner you spot the problem, the more likely it is that you will be able to save your plants.

brown leaves and early symptoms of box blight

Box blight is the most serious of a number of infections which can present problems for box.

However, all is not lost – the good news is that box blight does not affect the plant roots, only the above-ground growth.

Identifying Box Blight

First things first, it is important to be able to spot box blight and identify it correctly.

buxus with box blight and brown leaves next to a healthy plant
magnified close up of box affected by blight

When buxus is infected with box blight:

  • Spots will appear on the leaves.
  • Leaves turn brown and fall off, leaving bare patches.
  • Black streaks and dieback will be visible on young stems.
  • In wet conditions, you may also be able to see white spore masses of the fungus under infected leaves.
dead branches, brown leaves and visible white fungus caused by box blight

Another fungal disease, Volutella blight, may initially be confused for box blight.

This too leads to twig and leaf dieback – but black streaks characteristic of box blight do not form and the shrubs will not typically lose their leaves with this infection.

One other key way to tell box blight apart from this somewhat less serious problem is that in the case of Volutella blight, the fungal spore masses under the leaves will be pink and not white.

Preventative Measures

While you can often rescue buxus which has a box blight infection, of course prevention is better than cure.

Box blight spreads very easily, and can still arrive in your garden in spite of your best efforts.

But there are certain things you can do to make it less likely that box blight will arrive, reduce the chances of it taking hold, and make it easier to manage the problem if it does.

Avoid Introducing It Into Your Garden

topiary planters in a garden centre
Quarantine box coming from garden centres
  • If planting box, choose somewhat more resistant varieties. All Buxus ssp. are susceptible to box blight and none are highly resistant. However, B. microphylla varieties are generally less susceptible than B. sempervirens. Common box and its dwarf form ‘Suffruticosa are extremely susceptible. ‘Faulkner’ is one variety available in the UK that is said to be somewhat more resistant.
  • Make sure you quarantine new box plants for four weeks to make sure they are free of infection before you introduce them to your garden. Ideally, avoid the risk of importing new plants by propagating healthy plants in your own garden rather than buying additional plants.
  • Sanitise tools, equipment and garden wear to make sure you do not spread disease from one area of your garden to another. (Box blight will likely have already been present for some time before symptoms emerge, so practice good garden hygiene even if you have not yet spotted an infection.) If you have a gardener then it is important to make sure they do the same, and are not spreading infection between gardens.
  • Make sure people come into contact with box as little as possible. Especially in areas with visitors, place box topiary where it is not brushed past or handled so frequently. Make sure paths are wider where lined by box hedges to reduce human contact. This also improves airflow.

While blight can still arrive in your garden, taking these steps will help manage the risk and could keep your garden box blight free.

Create Less Favourable Conditions

healthy circular box which has been heavily mulched
  • Diversify – avoid planting very long box hedges that the disease can move along. And do not surround box topiary with box hedges. Separate areas of box with other planting.
  • Plant box in well-ventilated areas, free from damp and shade where the fungus will thrive.
  • Plant box avoiding overcrowding between it and other plants, and increase plant spacing when placing the box itself for better airflow.
  • Water early in the day if possible. And avoid watering from overhead to make sure the foliage does not get as wet.
  • Mulch under the box plants to cover fungus inoculum and reduce the chances of fungal spores splashing up from the soil onto the leaves.
  • Prune box to increase distance between leaves and the ground.
  • And trim to create hedges etc. with convex rather than flat tops. (For better water runoff which may help reduce the severity of box blight.)
  • Always undertake pruning and trimming in dry weather conditions.
  • Trim/ prune less frequently (for lower density and more open structure).
  • Feed plants moderately, and not with a high nitrogen feed. Choose an organic formulation specifically for box for optimal plant health.

Treating A Minor Box Blight Problem

hand shown pruning buxus shrub with secateurs

If you do see box blight in your garden, you must deal with the problem as soon as possible.

The quicker you are able to tackle the problem, the more likely it is that plants can be saved and the easier containment will be.

If you spot box blight:

  • Remove all affected sections from the plant, cutting back to healthy growth, and a little further.
  • Clear up all plant matter and surrounding debris. You might use a vacuum cleaner to suck up all leaves that fall to the centre of the plant where branches are too dense to access these easily. Scrape off all existing mulch and the surface of the topsoil where fungus is harboured.
  • Bag up all this material and dispose of it carefully. Take great care not to spread the infection to other parts of your garden, and keep material clear of your composting system.
  • Sterilize all tools, shoes and clothing so you do not spread the fungus to other parts of the garden.
  • Add a new soft, natural mulch (Topbuxus carpet, for example) around the plants.
  • Fertilise plants with a multi-purpose of Buxus specific organic plant feed to promote healthy new growth. The healthier the plants are, the easier it will be for them to stave off infection.

Since it is likely that other areas not yet showing symptoms will be affected, you will probably not immediately eradicate the problem, but you can reduce spreading.

You can also repeat this process as and when other symptoms show.

Treating A Major Box Blight Problem

large pruning shears being used to cut back box

Unfortunately, sometimes a major box blight problem can set in before gardeners are aware of the problem.

In some cases, it may be best to cut your losses and remove the affected plants entirely.

However, in many cases, even a box hedge or piece of topiary with many affected areas can still be saved through careful and yet rather drastic action.

  • Hedges and parterres of box can sometimes be saved by reducing height by around half, and perhaps width as well – cutting back to a few centimetres below any black streaks on stems and as above, carefully bagging and removing affected material. This includes dead leaves inside the plants, mulch, leaves on the ground and the top layer of soil. As above, hygiene is crucial, and great care should be taken not to spread the disease.
  • Again, promote healthy recovery by mulching, and feeding with an organic plant feed suited to box. Remain vigilant for further signs of infection.

In some cases, even chopping back this much may not be sufficient.

With severe cases, you may need to take more drastic action to save prized box plants.

In this case you might:

  • Cut back all plants showing symptoms right down to ground level, leaving just the stumps.
  • And clear up, mulch and fertilize as above.

Buxus Alternatives

small euonymus fortunei shrub on garden gravel
Euonymus fortunei

In areas where box blight is a major problem, or where serious outbreaks have already occurred, it is usually easier to forgo box altogether.

When choosing new plants, or replacing box, it is best to choose alternatives rather than struggling on.

Some options include:

  • Berberis ssp.
  • Euonymous fortunei
  • Ilex crenata
  • Lavandula angustifolia
  • Lonicera nitida
  • Osmathus delavayi
  • Pittosporum ssp.
  • Rosemarinus officinalis
  • Santolina chamaecyparissus
  • Taxus baccata

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