Abstract/Summary

Since 2006 increasing numbers of mature and maturing Oak trees, both in forest and urban settings have suffered from bleed canker to the main stem. The event has been described as part of a syndrome named Acute Oak Decline in 2009. The syndrome involves an interaction between invasive beetle larvae of Agrilus biguttatus and pathogenic bacteria causing bleed cankers. This is reported to potentially result in the demise of an infected tree within a five -year period. From an epidemiology study of 1 hectare of semi ancient natural woodland containing 192 maturing Oak trees it was seen that the bleed exudate occurred without the presence of the Agrilus beetle. The bleed exudate was seen to readily transfer through the Oak population over the 6year period. A significant proportion of the trees with the bleed exudate entered remission and that no connection was directly established between the death of the trees and the bleed canker alone. Tree ring analysis from a portion of the trees in the epidemiological study revealed that those trees that were symptomatic (with the bleed canker) did not exhibit a pre-disposition of reduced vitality and that those trees that showed recovery were predisposed to have smaller growth rings. Soils analysis revealed that the soils within the woodland were acidic, with low levels of Calcium. Initial experimentation showed that Calcium amendment to the soils reduced the amount of bleed canker. Three different bacterial species isolated from the bleed cankers were able to reproduce the bleed symptoms in pathogenicity tests, individually and in combination. However, the results were not consistent to satisfy Koch’s postulates. In consideration of potential biocontrol for the bleed canker a study of the culturable fungal endophytes within the main stems of symptomatic and non -symptomatic trees was carried out. This identified prevalent Penicillium sp. which in vitro were found to effectively suppress two of the three pathogenic bacteria identified as causal of the bleed exudate. Given the independence of the Bleed Canker as a pathogenic agent exclusive of the general syndrome named Acute Oak Decline, it is proposed that the bleed canker is identified as Oak Bleed Canker.