How to control box blight

If you have common box growing in your garden, either as hedging or topiary then box blight is something you should both be aware of and know how to identify quickly. Why? Because it is an incredibly destructive and fast acting disease which leaves a significant amount of damage in its wake.

Box blight is the common name given to two fungal species - Cylindrocladium buxicola (syn. Calonectria pseudonaviculata) and Pseudonectria buxi. They thrive on topiaried box and formal box hedging as the regular cutting of box pants encourages very dense, compact growth. This restricts air movement and increases humidity within the plant which favours fungal growth.


Cylindrocladium buxicola spores -
The most obvious symptoms are the appearance of bare, brown patches which are found on the surface and interior of box plants in August and September. However there are earlier signs which can indicate an infection which are chocolate coloured marks appearing on the healthy leaves, followed by the leaves turning grey, then brown before collapsing and rotting.

In wet conditions fungal spores may also be seen on the undersides of infected leaves. White spores indicate an infection of Cylindrocladium buxicola, while pink spores indicate an infection by Pseudonectria buxi.

Cylindrocladium buxicola is the more damaging of the two and can also infects young stems causing black streaks and die-back.

On vigorous specimens it is possible for new growth to regrow but without action the plant will become infected the following year, starting a cycle that will eventually kill the plant.


Both types of fungi require humid, warm conditions to thrive. Pseudonectria buxi enters the plant through open wounds - such as those created when box plants are clipped. Cylindrocladium buxicola is able to infect unwounded plants affecting both woody stems as well as the foliage.

Cultural control of box blight

Box blight -
The best cultural solution is to cut out all affected growth and (along with any fallen leaves) incinerate. Then remove the surface mulch or soil (which harbours overwintering spores) and either burn that too or take to your local recycling depot.

Of course this can seriously affect the shape of hedges and topiary and still may not remove all infected plant material or spores. Be aware that the spores can remain viable on fallen leaf litter for at least 6 years! In an serious outbreak you only option may be to remove and destroy all affected plants.

Reduce the amount of times that box plants are clipped to produce a more open habit as this will help to improve air circulation throughout the plants. Also avoid overhead watering as Cylindrocladium thrives in humid conditions. There isn't mush that you can do about rainfall but whenever watering is required only water at the base.

Chemical control of box blight

Box blight -
Applications of systemic fungicide can be used to control box rust and this is arguably the most effective course of action. For best results you can employ a contractor with a commercial pesticide licence who will apply a commercial fungicide (such as Signum) to your box plants.

If you wish to spray yourself using shop bought produces then consider using Scotts Fungus Clear Ultra, Bayer Fungus Fighter and Bayer Fungus Fighter Plus which can be applied when the new growth appears in the spring.

Always go by the application instructions on the box although there is anecdotal evidence that spraying once a month during the growing season will give effective results. If you are struggling to find these particular products at you local plant retailers then consider using Bayer Garden Multirose Concentrate 2 or Scotts Fungus Clear Ultra. Neither of these fungicides are listed on the packet as being suitable for the control of box blight but they do contain similar active chemicals as the previous products and can still be used to control box blight, although at owner's risk.

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