What is box blight?
Box blight is a disease of box leaves and stems caused by two fungi, Cylindrocladium buxicola and Volutella buxi. The two are often found together.
This is a disease specific to Buxus spp. (box).
Blight is just one of a number of problems box suffers from.
Cultural control and hygiene
Hold any commercially sourced plants in isolation for at least three weeks to confirm they are free of infection before planting out. Commercial nurseries may use fungicides which suppress but do not kill the fungus and this isolation technique will allow time for any suppressed disease to become visible.
If the disease does break out, remove and destroy affected plants. If they are mature and highly valued, cut out all affected parts, clean up fallen leaves (including stripping and replacing surface topsoil to ensure complete removal) and treat with a fungicide.
Unfortunately there is not known to be a resistant Buxus at present.
The host range of both fungi is not fully known, but C. buxicola attacks Buxus balearica, B. bodinieri, B. glomerata, B. harlandii, B. microphylla, B. macowanii, B. riparia, B. sinica and B. sempervirens. Other plants in the Buxaceae family may be susceptible such as Sarcococca spp.
Choose alternative hedging and topiary plants
To be completely safe, choose an alternative hedge or topiary plant. The following all have small leaves and can be clipped into formal hedging styles:
There are no fungicides available to amateurs with specific recommendations for use against box blight. However, the fungicides difenoconazole (Westland Plant Rescue Control), myclobutanil (Bayer Garden Systhane Fungus Fighter and other products), tebuconazole (Bayer Garden Multirose Concentrate 2) and triticonazole (Scotts Fungus Clear Ultra) are labelled for control of other diseases on ornamentals and could therefore be used legally on box (at owner's risk) to try and control box blight. Research undertaken by the RHS has investigated myclobutanil and found it to be ineffective at controlling Cylindrocladium blight.
Fungicides for gardeners (Adobe Acrobat pdf document outlining fungicides available to gardeners)
The fungi survive as resting structures or mycelium on fallen leaves and produce spores when conditions are suitable. The spores are dispersed in water and probably by animals and birds. They may be spread in wind-blown rain, but are unlikely to travel long distances on the wind. As well as natural means of dispersal, these fungi have been spread widely by human activity, especially on infected plants from nurseries.
V. buxi requires wounds for infection and is associated with clipping. C. buxicola can infect unwounded plants and causes more serious damage.
V. buxi has long been known, but little studied. C. buxicola was first recognised in the UK in the mid 1990s and has also broken out in northern Europe and New Zealand, but its origin is unknown.
Both fungi can infect the very common Buxus sempervirens and several other species.
RHS research into box blight