LARCH trees in Chawton Park Wood, at Medstead, will be felled during September to help control an outbreak of a deadly tree fungus.

The trees are dying of ramorum disease, caused by a fungus-like organism called phytophthora ramorum, and cutting them down is the only way to limit its spread to other trees and plants.

Owned by the Forestry Commission, the 730 acres of diverse ancient woodland stretches from Boyneswood Road and Abbey Road in Medstead in the west, running north east toward Northfield Lane in Alton, and is a favourite haunt for dog walkers, hikers, cyclists, runners, horse riders, and nature lovers.

It is also a working wood, subject to selective felling, although in this case the aim of the exercise will be disease control.

According to Forestry Commission South England district manager Bruce Rothnie, ramorum disease is destructive to many other species and the commission has a “legal obligation and a duty” to neighbouring landowners to remove the infected trees as quickly as possible to protect other trees and plants.

He continued: “This is part of our tried-and-tested approach to disease control which has successfully slowed the spread of the infection to reduce tree losses. We will also ensure new trees will be grown in their place as quickly as possible.”

In the case of Chawton Park Wood, the felling programme is expected to be fairly well contained.

Mr Rothnie said: “We are fortunate that only a relatively small area of the woodland will be affected – about four hectares (10 acres) – and that Chawton Park is already a diverse woodland, so the overall impact on the woodland will be no greater than that of a normal forestry operation.”

The affected area, which includes a section of the Sustrans cycle route (23), linking Alton to Four Marks and Medstead, will be cordoned off for safety reasons during the felling operations, with alternative routes signposted. The remainder of the woods will remain open to visitors, and Mr Rothnie said the work and the access restrictions should be finished by the end of September.

He encouraged woodland owners, park managers and gardeners to familiarise themselves with the symptoms of ramorum disease and the plants it can affect, and to inspect their trees and plants regularly.

Thought to have originated in Asia, and first found on plants in Britain in 2002, the symptom on trees of phytophthora ramorum include lesions, sometimes known as bleeding cankers, which leak fluid from infected bark, visible as a black exudate which can dry to a crust on the trunk. The inner bark under this bleeding area is usually discoloured and dying. Trees die when the lesions become extensive on the main trunk.

Shoots and foliage can also be affected, visible as wilted, withered shoot tips with blackened needles. The infected shoots shed their needles prematurely. Trees with branch dieback can have numerous resinous cankers on the branches and upper trunk.

On other plants, the disease infects the leaves and shoots of ornamental shrubs such as rhododendron, viburnum, pieris and camellia. Although it does not usually kill these plants, infected leaves of some of these “foliar hosts” can generate many spores, and in sufficient numbers these spores can then infect the bark of certain tree species.

Typical symptoms on rhododendron include leaf-blackening, wilted shoots and dieback. On individual leaves, blackening of the leaf stalk usually extends into the leaf along the mid-vein, although blackening at the leaf tip can also occur. The progress of the disease can be so rapid that shoots wilt and the leaves hang down.

Evidence indicates that phytophthora ramorum can be spread over several miles in mists, air currents, watercourses and rain splash. It is also know that phytophthora pathogens can be spread on footwear, dogs’ paws, bicycle wheels, tools and equipment. Movement of infected plants is also a key means of spreading it over long distances.

Sometimes known as ‘sudden oak death’, susceptible trees include larch, certain strains of oak, beech, sweet chestnut and horse chestnut, as well ad Douglas fir and Sitka spruce.

Simple precautions such as cleaning footwear, tools, vehicles and clothing are strongly advised in outbreak areas to prevent further spread.

There is no current cure and there are no effective chemical treatments available to combat the disease. The best available scientific advice is to remove and kill the living plant tissue on which the organism depends for reproduction. In the case of infected larch, this means affected trees should be felled or otherwise killed as quickly as possible after detection of the disease and before the next spring or autumn period of sporulation begins on the needles.

The public are urged to report any suspicious symptoms on trees to the Forestry Commission and on other plants to the Animal and Plant Health Agency.

Mr Rothnie said: “The sooner we can identify and tackle a problem the better we can protect other trees and plants in the area from this disease.”