There are two organisms which cause Blight in the Genus Buxus; both are fungal and they can occur together. Volutella has been around for many years. It is caused by Volutella buxi resulting in browning of the leaves and dieback of branches leaving bare patches in hedges and topiary specimens. It spreads in wet humid conditions - pinkish spores appear on the undersides of leaves and are carried in water splashes to new sites. Fallen leaves carry the disease over the winter and new spores are produced in the spring. They enter the plant through clipping cuts and other damage to leaves and stems.
The other Box Blight, which is more serious, has only been recognised in the British Isles since the mid 1990s, but is causing great concern. The fungus Cylindrocladium buxicola produces symptoms similar to Volutella with defoliated plants. The leaves develop dark brown spots which enlarge to affect all of the tissues, patches of greyish fungal growth appear on the underside and asexual spores (conidia) are soon released to spread the infection. Black streaks appear on the stems. The spores are capable of penetrating the cuticle so wounding is not necessary for infection to occur.
The disease requires moist conditions to thrive - the asexual spores die in dry conditions. Viable spores have been found in decomposing leaves after nearly a year, so any debris should be burnt if possible - never add to the compost heap.
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