Guarding against tree disease in Welwyn Hatfield

New saplings planted on Parkway close. (Image: Danny Loo Photography 2017)

In December, officers warned elected members that trees of many species in county council ownership were increasingly at risk, and estimated the potential long term cost across Hertfordshire at £10 million.

Chalara, a fungal disease otherwise known as ash dieback, was not fully scientifically described until 2006, but by the time of the first British cases six years later, had already spread across much of eastern and central Europe.

As the disease has no treatment and ash is the most common species in the county, the potential impact on Hertfordshire is very serious - and the County Hall report named Welwyn Hatfield as one borough at risk.

Other tree threats that have arrived in Herfordshire in the last decade from overseas include the oak processionary moth and the oriental chestnut gall wasp.

One of the diseased trees on Parkway. (Image: Danny Loo Photography 2017)

According to the report: “The UK is currently under threat from an increasing number of tree pests and diseases.

“[These] are affecting, or have the potential to affect, an increasing range of native trees from urban parks, streets and gardens to woodlands, highways, schools, nature reserves, hedgerows and the wider landscape.”

Councillor Helen Bromley, Welwyn Hatfield Council cabinet environment chief, said: “The dramatic increase in pests and diseases across the UK is presenting new challenges for everyone involved in maintaining trees. We’re responding to this by regularly monitoring, liaising with county and regional colleagues.”

The Forestry Commission has confirmed that Chalara has affected ash tress in two borough-council owned woodlands on the fringe of WelwyGC - Sherrardspark Woods and The Commons, although in fewer than 20 specimens in total.

Victims of ash dieback in The Commons nature reserve, pictured in August 2016. (Image: Archant)

Councillor Bromley continued: “We are responsible for tens of thousands of trees across the borough and these are maintained on a three-year rolling programme, assessing their health and structural condition.

“Any pruning or maintenance works considered necessary for the health of the tree or for the safety of people are recorded and undertaken on a priority basis.”

Although the fungal bark infection known as bleeding canker has been known in Britain since 1990, it exploded in the early years of the millennium, and affected about half the horse chestnuts in the country by 2007.

The borough council is monitoring the disease in 629 urban horse chestnuts - and aroused vigorous opposition just last summer, when it announced it wanted to cut down several infected specimens along Parkway, although eventually a compromise satisfied most of the campaigners, with replanting due to complete this spring.

Councillor Bromley continued: “We are following the advice given by Forestry Research on the progress of the infection, and sadly have had to fell a small number of infected trees.

“As many as possible have been replaced with Liquidambars, a species that is less susceptible to disease, and takes well to the natural ecology of Welwyn Hatfield.”

The County Hall report blames the recent spread of tree disease on climate change and the import of exotic plants - neither of which is likely to slow in the immediate future, so these problems seem likely to accelerate.

And with publicly and privately owned trees so vital to the character of Welwyn Garden City in particular, how can we be confident in their future? Councillor Bromley insisted: “We follow the latest government advice to help limit and monitor the spread of diseases that can threaten trees in the borough.

“Our team remains vigilant and will report any signs of disease to the Forestry Commission where needed. We also keep up to date with the latest outbreak information and will also consider the use of alternative plant species in planning applications to minimise the number of susceptible trees in the borough.”