Here is an extract from a letter received from the Forestry Commission:
I am writing to you with information about an outbreak of sweet chestnut blight in the South West and to notify you of four 5km zones that are subject to movement restrictions.
Sweet chestnut blight is caused by a fungus called Cryphonectria parasitica, which gets into the trees through wounds or graft sites. Although oak trees suffer very little damage if they are infected by the fungus, they can spread it, so restrictions on movements of oak material are also required as a precaution.
Sweet chestnut blight was found in Devon in December 2016, initially south of Exeter. We wrote to our Devon contacts in January to inform them and again last week to let them know about two restricted zones; you may have seen articles in the forestry or local media about this. As a result of related survey and tracing work, we have now identified another zone in Devon and one in Dorset where restrictions are required. We are now writing to all our South West contacts to let you know what we are doing to manage the outbreak and to inform you about the movement restrictions.
For further information go to: https://www.forestry.gov.uk/chestnutblight