Fungal disease 'prevalent' on trees in Hertfordshire new report confirms
Highways officials say the fungal disease ash dieback is now “prevalent” in Hertfordshire, with more than a third of ash trees affected – five times as many as four years ago.
The condition – first detected in England in 2012 – causes leaf loss and dead branches throughout the crown of ash trees. Although some with the condition survive, large numbers die.
Hertfordshire County Council (HCC) officers have been monitoring the impact of ash dieback – also known as hymenoscyphus fraxinea – on trees lining the county’s road network since 2020.
According to a report, 32,408 ash trees line the county’s roads. Of those, 11,433 (35.3%) were recorded in 2025 as having ash dieback.
“We have been monitoring the impacts of ash dieback over the past six years through targeted inspections and recording condition to quantify the regional impact and spread of the disease,” says the report. “Our findings show the disease has been slow to spread through Hertfordshire but is now prevalent.”
In 2022, ash dieback was confirmed in 2,205 ash trees along Hertfordshire’s highways. Of those, 41 were dead. The extent of the canopy dieback was up to 50% in 1,682 of the trees and over 50% in 372. However, the latest data shows that of the 11,433 recorded cases last year, 491 trees were dead, 8,871 had up to 50% canopy dieback and 2,024 had canopy dieback of more than 50%.
There are 297,000 trees in the council’s highways estate and it conducts up to 60,000 tree inspections every year. The latest findings are included in HCC’s ‘Highways Infrastructure Asset Management Plan, Asset Performance Report 24/25’, an official update of policy, strategy and serviced changes, which was considered and agreed by the council’s cabinet at its meeting on Wednesday.