Insects and diseases affecting trees and hedges

Trees and hedges may be affected by a range of diseases and insects. To read more about these, visit the Forestry Commission website.

Oak Processionary Moth in Kingston

The Oak Processionary Moth (Thaumetopoea processionea) is an invasive species which has health implications to trees, humans and animals. Native to central and southern Europe, this pest has been identified in London and is breeding on oak trees in West and South London. It gets its common name from its caterpillars' striking habit of forming long lines, or 'processions', in trees and other substrates.

The area affected by Oak Processionary Moth is growing steadily and has been identified within Kingston Upon Thames and neighbouring boroughs.

You must not attempt to handle the larvae caterpillars yourself, or disturb their nests.

The caterpillars have irritating hairs that carry a toxin which can be blown in the wind and cause serious irritation to the skin, eyes and bronchial tubes of humans and animals. They are considered a significant health problem.

The current management process includes removal of any nests up to 4m which ensures they are out of reach of humans and pets. We carry out an annual survey on all RBK oak trees for Oak Processionary Moth. This takes place in the summer and takes the form of a visual inspection from ground level to identify any nests which would pose a health and safety risk - these are currently being removed.

The council will generally only remove nests high up within the canopy of the tree if the tree has reached plague levels of infestation and the tree becomes overladen, showing signs of severe defoliation.

The Forestry Commission announced in 2011 that it's no longer possible to eradicate the West and South-West London outbreak and the ongoing objective is to prevent or slow its spread to keep its population as low as possible.

Residents can report sightings by emailing: environment@kingston.gov.uk.

Ash dieback (Chalara fraxinea)

Ash dieback is a serious disease caused by a fungus called Chalara fraxinea. The disease causes leaf loss and crown dieback in Ash trees, and usually leads to tree death.

Young trees cannot recover from infection, but mature trees can survive for a considerable time and some may recover entirely. The impact of Chalara fraxinea depends on tree age, location, weather conditions and co-presence of honey fungus or other pathogenic organisms.

Issues affecting Poplars

Poplar trees have been in the UK for many years but were mass planted during the post-war development period because they established easily and grew to a large size quickly. We now know with some types of poplar, this fast growth is at the partial expense of wood strength. This means they're more likely to snap and fail in high winds than other tree species.

Poplars have a typical lifespan of 50-80 years in urban environments. The majority of our stock is reaching this age. This is a challenge for all local authorities across the country where poplars were widely planted at the same time in built up areas.

Kingston began actively undertaking detailed annual surveys of poplars in high risk locations from 2016 after a very large poplar fell at Dysart open space during the middle of the day. Following these surveys it was noted that some trees required extensive pruning, and in some cases removal, to reduce the hazards and risks posed by these trees.

168 poplars have been removed since 2010. All of these trees were assessed and found to be in a state of decline and had to be removed as they posed a safety risk.

We have 180 poplars (lombardy, balsam and hybrid) left in the borough on public land plus large groups of aspen and white poplars at Elmbridge meadows and Raeburn Avenue open space. High risk locations include parks and playgrounds at RAF Chessington, Blagdon Recreation Ground, Canbury Gardens, Malden Green and Dysart open Space.

It is important for us to manage poplars carefully in well used spaces because they have an unpredictable and brittle nature as described above. Where possible, we manage them in a way that enables us to stagger removals and keep trees for as long as possible and mitigate impact on bats and birds.

However, safety must be the priority consideration at all times. Our poplar trees are surveyed annually to assess their general condition, to record defects and to make recommendations for safety and maintenance work, where necessary.

It is important to remember that the risk from trees can never be completely removed. To do so would result in the unnecessary loss of trees and their benefits. Good tree safety management simply reduces the level of risk to a reasonable level.

The fungi that is frequently associated with poplars is called Ganoderma. This fungi specialises in degrading lignin within the tree, which leaves the internal wood soft and stringy. It's often found in built up areas and parks and very often associated with weakened or damaged trees. This means any injuries (i.e. animal damage, branches breaking, root disturbance) can be readily exploited by this decay fungi.

Poplar's are extremely poor at defending themselves against this fungi and are quickly hollowed out by it. Trees can appear healthy from the outside but a detailed inspection can reveal significant defects that affect the structural stability of the tree. Below are photos of decayed stumps from poplar trees felled in Kingston which all appeared healthy before further investigation. The hollowed out stumps show just how much damage to the centre of the tree can be caused, which clearly poses an increased risk of the tree falling over.

Another issue affecting poplars is infestation by the poplar hornet moth). Whilst this is not a sole reason to remove a tree, the larvae feeds on the part of the tree that produces new growth every year. Where there are extensive infestations, the tree must be monitored and assessed annually for any signs of decline. Additionally, when the larvae exit the tree they create holes that can act as entry points for decay fungi.