Acute oak decline is a disease that infects oak trees in the UK. It mainly affects mature oak trees of over 50 years old of both Britain's native oak species: the pedunculate oak (Quercus robur) and the sessile oak (Quercus petraea). The disease is characterised by the trees bleeding or oozing a dark fluid from small lesions or splits in their bark. Unlike , acute oak decline can lead to the death of trees within 4 to 5 years of symptoms appearing. The number of trees affected is thought to number in the low thousands, with a higher number of infected trees being found in the Midlands. It is thought to be caused by a bacterium; it is currently not known which species is involved, but scientists are actively trying to discover what is responsible. At least three genera of bacteria are possi