The disease is characterised by the trees bleeding or oozing a dark fluid from small lesions or splits in their bark.

Two different species of bacteria, Brenneria goodwinii, Gibbsiella quercinecans, are repeatedly found in the decaying tissues of trees with AOD.

[3] Laboratory experiment confirmed that these two species have the ability to cause tree tissue necrosis and possess virulence genes commonly found in plant pathogens.

[4] In addition to these two bacterial pathogens, the other microbes present in AOD affected trees is different from non-infected ones.

[5][6] Most trees affected by AOD will display exit holes and galleries caused by the larvae of the two-spotted oak borer Agrilus biguttatus[7].