Swiss oaks hit by root and trunk diseases

Oak trees are having a hard time in Switzerland. Keystone

A new root disease is giving oaks a hard time in Switzerland. Last year, scientists identified Phytophthora root and trunk diseases on Swiss oaks for the first time. 

 It is particularly worrying that this root disease is appearing at the same time as acute oak decline, said Swiss Forest Protection on Tuesday, a specialist unit of the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL). 

Oaks are considered to be promising species, as they suffer little from the consequences of climate change, such as heat or drought, compared to other broadleaved trees. 

However, the situation is particularly worrying because two diseases are now attacking oaks at the same time. Acute oak decline, caused by various bacteria, was first detected in Switzerland in 2017. 

Since then, Swiss Forest Protection has received numerous reports of this disease in all regions of the country. It is currently the main cause of reports of oaks showing mucus discharge from the trunk and sparse crowns. 

WSL scientists examined all the oaks suffering from acute dieback for root and trunk diseases of the Phytophthora genus, as the symptoms of these diseases are similar. In 2023, two tests were positive for root disease. 

Both cases originated in urban areas, and in both cases the Phytophthora cinnamomi species was present, although until now it was only known as the pathogen of ink disease on chestnut trees in Ticino. 

According to specialists, it is worrying that one of the two cases originated north of the Alps. Until now, it was thought that this pathogen could not establish itself there due to the generally too low temperatures in winter.