On 19 August 2026, the Forestry Commission announced an extension of the demarcated area for Sweet Chestnut Blight in Devon and into a small part of Cornwall, following further findings close to the existing restricted-zone boundary. The expanded area, covering West Devon District and the South East Cornwall constituency, was due to come into force on Wednesday 26 August 2026, with trading restrictions on sweet chestnut trees and other susceptible material applying across it.

The Commission said continued surveillance had confirmed additional infected sites whose buffer zones extend beyond the previous boundary. A finding in October 2025 was the first occurrence of the disease with sexual sporulation present since 2011, and the newer outbreak sites also show evidence of sexual sporulation, meaning more airborne spores are being produced and the risk of wider spread is significantly raised.

Defra Chief Plant Health Officer Professor Nicola Spence said the risk had increased significantly in parts of the South West and urged owners and workers of sweet chestnut trees to remain vigilant and report signs through TreeAlert. Andrea Deol, the Commission's Head of Plant Health Forestry, said restricting movement of susceptible material is among the most effective tools to slow spread, and encouraged public support for the Check a Sweet Chestnut campaign, run with the Royal Horticultural Society and Forest Research.