If you get Box Blight, CAREFULLY dig up and burn the affected plants including all dropped leaves. If this is not possible, bag the plants and contact your local authority who should offer a safe way of disposing of the material. Never, ever compost them either in your own garden or at any other facility. However, the RHS also states: “If the infected plants 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.” It’s a long shot and viewers of BBC’s Gardeners’ World will know that presenter Monty Don did not take it when his Box became infected.
The following fungicides are available to amateur gardeners under various brand names and can legally be used against Box Blight, though there is no evidence to suggest any of them are effective: difenoconazole, myclobutanil, tebuconazole and triticonazole
Finally, do not replant Box in a garden that has been infected for at least six years as the fungi can survive in situ for this long