The risk of Sweet Chestnut Blight spreading has increased significantly in parts of south-west England, the Forestry Commission has said.

Restrictions aimed at preventing the spread of the disease have been extended across parts of Devon and Cornwall with the new area coming into force on 26 August. They expand the existing area in south Devon into the west of the county and into south east Cornwall.

It follows surveillance which discovered further infected sites close to the existing restricted zone.

Trading restrictions on sweet chestnut trees and other chestnut material will apply across the expanded area to help prevent infected plants and materials being moved, the commission said.

The first restrictions were introduced in south Devon in April but the disease has spread, according to Defra.

Nicola Spence, the agency’s chief plant health officer, said: “The risk of Sweet Chestnut Blight spreading has increased significantly in parts of the South West.”

She said extending the area was “a necessary step to help protect sweet chestnut trees” and urged people to report signs of disease through TreeAlert.

The Forestry Commission said a discovery in October 2025 was the first case of the disease, while further infected sites had also shown evidence of the process.

Sweet chestnut blight is a fungal disease caused by Cryphonectria parasitica that attacks the bark of sweet chestnut trees, cutting off nutrients and usually killing the tree above ground within a few years.

Andrea Deol, head of plant health at the Forestry Commission, said restricting the movement of susceptible material was “one of the most effective tools we have to slow the spread of this disease”.

The public, woodland owners and land managers are urged to check sweet chestnut trees for signs of the disease and report suspected cases through the TreeAlert portal as part of the Check a Sweet Chestnut campaign.