Dr. Ned Tisserat, Extension Plant Pathologist, was asked by the city forester in Boulder to come take a look at some Red Oak trees that were declining in one of the parks in the city. The symptoms are branch dieback with borer holes in the trunks of the trees. After further investigation, it appears that the branch dieback may be associated with Kermes scale, but the borer holes in the trunk caused by a flat-headed borer were unusual. Dr. Tisserat isolated Fusarium solani from an area surrounding the borer galleries, but also noticed a gummosis on the branches. This gummosis was in close proximity to the Kermes scale. Isolations were done and the gummosis was the result of a bacteria which was identified as Brenneria (Erwinia) quercina. This bacterium has been previously associated with 'Drippy Nuts Disease' on oaks in California and with an oak decline in Europe. More investigation is needed to understand if the Kermes scale is contributing to the bacterial infection, where the bacterium is originating from and how the flat-headed borer is involved in the infection process, if at all.
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