Author: Mick Biddle , Tree Health Officer
Hello, I’m Mick Biddle; I am the Forestry Commission’s Tree Health Officer for the SW of England. My role involves the specialist surveillance and detection of quarantine tree health threats. Over the last year, I and the rest of my team have been very busy after a recent finding of a new pathogen to the UK – sweet chestnut blight.
At the very end of 2016, chestnut blight was confirmed on some sweet chestnut trees in a car park in Devon, discovered by one of my colleagues from APHA. Since then, our specialised survey and detection work has brought to light a number of subsequent findings. With each finding, the Tree Health Team has had to undertake intensive surveys of trees in the surrounding area.
Sweet chestnut blight is caused by a fungus called Cryphonectria parasitica which is widespread in many countries worldwide. This fungus can have severe effects in chestnut (Castanea) species – the American chestnut (Castanea dentata) in the USA has been almost completely wiped out as a result of this disease. Although it doesn’t always kill affected trees, our European sweet chestnut (Castanea sativa) is highly susceptible, and it can affect the quality of the timber even if the tree survives an infection. The disease has been known in other countries to affect some species of oak (Quercus) and other species although its impact in these trees seems to be much less severe. It does not affect Horse chestnut trees (conker trees) which belong to the Aesculus genus, and it is not harmful to animals or people.
I have been working with colleagues in Forest Research to map, record and sample affected trees; the scientific understanding of the disease dynamics in this country is essential to be able to manage it effectively. Forest Research are also hard at work carefully screening all of our samples for the presence of “hypovirulence” – a naturally-occurring virus which can affect the chestnut blight fungus, reducing its ability to spread and limiting the damage caused by the disease.
As we’re just out of winter, the most obvious symptoms of sweet chestnut blight to look out for are stem cankers causing sunken orange or bright brown patches, or ugly-looking cracked and swollen areas of bark, underneath which cream-coloured fan-like mycelia grow. You might also see tiny orange fruiting bodies which erupt through the infected back from the mycelia behind. These pin-head sized pustules exude orange-yellow tendrils of water-borne spores in moist weather, and can also produce airborne spores. Above the canker, leaves wilt and turn brown but often remain hanging on the tree. Below the canker, branches have healthy foliage and, after a short time, new shoots are produced below the area of dead bark. These epicormic shoots can be a sign that the stem has become completely girdled by the fungus.
This is an ongoing situation and as we understand more, advice will be updated. To keep up to date with the latest, you can check out our webpage on sweet chestnut blight.
As always, we recommend that everyone, whether a forester, arborist, or a woodland visitor, undertakes good biosecurity. As a previous post has highlighted, just by simply cleaning our boots, bikes, tools, etc. between sites, we can reduce the risk of spreading harmful pests and diseases. And if you do spot any symptoms of sweet chestnut blight or any other ill-health in trees, please report it to us via Tree Alert.