Chestnut blight

Chestnut blight was confirmed on European sweet chestnut (Castanea sativa) for the first time in the UK in 2011. Recent findings (2016) in Devon, Dorset and Kent highlight the continued threat posed by the pathogen. In the UK, the fungus is a notifiable pathogen and suspected cases of the disease must be reported to the relevant plant health authority.

Blight symptoms on sweet chestnut

Quick facts

Common name chestnut blight
Scientific names Cryphonectria parasitica
Plants affected mainly Castanea sativa and C. dentata. Also trees in the Fagaceae family including Quercus spp and Acer spp
Main symptoms cankers, wilting and dieback of the stems
Timing Bright orange pustules produced throughout the year following wet weather during mild conditions

What is chestnut blight?

Chestnut blight is a fungal disease caused by Cryphonectria parasitica. In the UK the disease poses a significant threat to about 12,000 hectares of woodland which has sweet chestnut (Castanea sativa) as the dominant tree species, most of which is located in southern England.

Chestnut blight has caused devastating losses in North America, where American chestnut (Castanea dentata) was eradicated from eastern North America in the first half of the 20th century because of the disease. The fungus was originally introduced from eastern Asia. Chestnut blight has also spread throughout continental Europe since it was first discovered in Italy in 1938.

Horse chestnut or ‘conker tree’ (Aesculus hippocastanum) is unrelated to Castanea and is not affected.

Symptoms

Some typical symptoms;

  • On leaves: The foliage wilts and dies as a result of girdling cankers lower down the stem
  • On stems: Striking contrast between green healthy and diseased orange bark on young stems. Underneath the bark buff-coloured fungal growth may be seen. Cankers (swollen or sunken) develop on the stems on which masses of yellow-orange to reddish-brown pustules, the size of a pin-head (fruiting bodies) are visible. The tree sprouts new shoots below the cankers which can also be affected
  • On whole tree: Cankers spread throughout the tree surface, killing the tree. Although young trees may succumb to the disease within a year, it may take years before mature trees eventually die. The root system is not affected

Control

Non-chemical control

If you suspect that chestnut blight is present in your garden you should not attempt to control the disease yourself. You should report your suspicions immediately to the relevant plant health authority. In England and Wales this is;

Chemical control

There is no chemical control available to gardeners for this disease.

Biology

Cryphonectria parasitica overwinters in lesions and colonized bark. The spores are produced in wet weather and at any time of the year pending mild temperatures. The spores are dispersed via wind, rain or vectors such as insects and birds. Infection is initiated when spores land on freshly wounded bark. The susceptibility of the host tissues decreases after a few days. The fungus kills the bark and cambium by a combination of mechanical and chemical actions. It is also reported that the pathogen can exist as a saprobe (i.e. it lives and feeds on dead organic matter) for at least two years on moribund bark. Long distance spread is by movement of infected plants, wood or bark. Risk of transmission by fruits or seeds is small.

There is also evidence that the pathogen can weaken in virulence in Europe and some American localities due to infection of the fungus by a virus (dsRNA hypovirus CHV1). The virus limits the ability of the pathogen to produce spores, reduces its growth and its ability to produce enzymes that kill the host tissues. This phenomenon, known as hypovirulence, allows the trees to recover. The discovery of hypovirulent strains of the fungus raised hopes for biological control of the disease. However the success has been limited because the virus does not spread readily between strains and hypovirulent strains do not compete very well with virus-free fungal strains. Scientists are working towards manipulating hypovirulence to develop it as an efficient method of biological control.

Image: © Forestry Commission Picture Library

Advertise here

Gardeners' calendar

Advice from the RHS

Find out what to do this month with our gardeners' calendar

Advice from the RHS

Did you find the advice you needed?

RHS members can get exclusive individual advice from the RHS Gardening Advice team.

Join the RHS now

Discuss this

for the site or to share your experiences on this topic and seek advice from our community of gardeners.