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Oak wilt (Ceratocystis fagacearum)

 

Ceratocystis fagacearum (C. fagacearum) is a destructive fungus which causes wilt in oak trees in eastern and mid-western states of the United States. It causes extensive damage, particularly to species in the ‘red’ oak group (Quercus section Lobatae; syn. Erythrobalanus), but it can also damage ‘white’ oaks (Quercus section Quercus).

The threat

There is strong evidence that European white oaks, including Britain’s native sessile and pedunculate or English oak (Q. petraea and Q. robur respectively), are also very susceptible to infection by the fungus and can be killed. It is therefore considered that it would pose a threat to oak trees and forests if it entered the UK.

Symptoms

Leaf scorch in oakThe first symptom to become visible is dieback in the crown of infected trees. In red oaks, symptoms begin to appear within weeks of infection, when yellowing of the leaves occurs, particularly along the veins. This is followed by ‘scorch’, or browning, typically starting at the tip of the leaf. There is a clear demarcation line between the dead and live tissues. Within a short time, the affected foliage of red oaks develops a false autumn colour as the tree wilts from the top downwards.

Elongated cracks are sometimes present on the trunks of infected, dying trees, caused by turgor pressure exerted by the formation of fungal sporulation mats under the bark. Infected red oaks can die within four to six weeks. (Turgor pressure is the water pressure inside plant cells.)

North American white oaks, however, have been known to recover from infection, or take many years to die. Fungal sporulation mats and resultant bark cracking are not usually seen in infected white oaks.

Susceptible species

Although only 16 of the approximately 600 species of Quercus species known are listed by EPPO as susceptible to damage by C. fagacearum infection, all 58 North American native oak species are known to be susceptible. The most susceptible species are ‘red’ oaks, all of which are native to North America.

The UK’s native sessile and pedunculate oaks are ‘white’ oaks, but are also known to be susceptible to C. fagacearum, dying within one year of inoculation with it (Pinon et al. 1997).

Other oaks planted in the UK and which might be susceptible include members of the Turkey oak or Cerris section (e.g. Q. castaneifolia, Q. cerris, Q. trojana) and members of the Mesobalanus section (e.g. Q. frainetto, Q. macranthera, Q. pyrenaica).

Tree species in several other genera within the Fagaceae family have also been reported to be susceptible to C. fagacearum in artificial inoculations, including North American and European sweet chestnut (Castanea dentata and C. sativa respectively), North American chinquapin (Castaneopsis sempervirens), and species in the tanoak genus Lithocarpus (Rexrode and Brown 1983). The North America bush chinquapin (Castanea pumila), and a species of Chinese chestnut, C. mollissima, are also natural hosts, dying rapidly after infection (Bretz and Long 1950).

Distribution

  • USA: Present in 26 eastern and mid-western states
  • Asia: No records
  • Europe: No confirmed record exists for this area. The pathogen is not present in the UK

Control measures

The control of imports of oak timber into the EU, in a general sense, is specified under EU Plant Health Directive 2000/29/EC, and implemented in Great Britain by the Plant Health (Forestry) Order 2005. This order provides the ‘principal instrument for managing the import of trees, wood, wood products and bark’, and specifies ‘Oak (Quercus) originating in the USA’ as a commodity.

The specific requirements related to imports of oak timber are summarised in our Timber and wood import pages. Any oak timber from the USA and Canada must be squared to remove the rounded surfaces, be bark-free, and be dried to less than 20% moisture content before being imported into the UK. In addition, it must be disinfected by an appropriate heat treatment, such as hot air or hot water, or kiln dried and labelled as such. Other woody oak material, such as chips, wood waste or scrap, must be similarly treated. No bark of oaks is permitted.

Some European countries have allowed the importation of bark-covered oak logs from the USA for veneer production. (EC derogation decision 2005/359/EC, extended to 2020 in 2010 by EC derogation EC 2010/793). However, this does not apply to any UK ports.

Action

Our Contingency plan sets out the actions which would be taken in the event of an outbreak of oak wilt being found in Great Britain.

Report a sighting

Although the oak wilt fungus is not known to be present in the UK, there is a risk of its being accidentally introduced. We therefore urge the public, and especially tree and plant professionals and importers of wood and plant materials, to remain vigilant for signs of it, and to report suspicious symptoms to us.

Tree Alert iconIf you think you have spotted the disease please tell us using Tree Alert

 










Last updated: 13th February 2018