Question to the Department for Environment, Food and Rural Affairs:

To ask His Majesty's Government what assessment they have made of the number of ash trees infected with the fungus Hymenoscyphus fraxineus in the year 2023.

The Government does not collect data on the number of individual ash trees that have become infected with ash dieback, but the disease is now present in all counties and is predicted to kill over 100 million trees in the UK. Hymenoscyphus fraxineus is spread via spores which can spread for considerable distances in the wind before infecting another ash tree. This means it is not possible to limit the spread of the disease. Some local authorities conduct annual surveys of ash trees to track local spread and decline and inform their management strategies.

In most areas, a majority of ash trees are now expected to be infected, but the response of individual ash trees to infection is highly variable. The most susceptible trees often die within a few years and the most resistant trees may show little damage and sometimes signs of recovery between years. The severity and impact of the disease at a local level also varies by tree age and condition, climate, the presence of secondary pathogens and other environmental factors.

From observations in Europe and the UK, we expect a minimum of 1-5% of ash trees to be naturally resistant to the disease. Resistance is heritable which offers hope for a future breeding programme and Defra is investing in R&D to support this.