Fungi Associated with Damage Observed on Branches of Juglans nigra in Indiana, Missouri, and Tennessee

Abstract

Branch and stem cankers caused by Geosmithia morbida associated with mass attack by its primary insect vector (Pityophthorus juglandis) result in thousand cankers disease (TCD) on Juglans and Pterocarya species. Because other fungi and insects can cause visible damage to Juglans nigra, a baseline assessment was performed to document damage types present and to characterize fungi associated with each type. Two branches were collected from trees with visually healthy crowns in TCD-free locations (Indiana and Missouri) and two branches from trees with and without crown symptoms characteristic of TCD within the disease range in Tennessee. In most cases, one of the two branches was girdled at the base 3 to 4 months prior to harvest. Outer bark was peeled from branch subsamples, observed damage characterized, and isolation of fungi from each damage type attempted. Three known pathogens of J. nigra were obtained from different damage types: G. morbida, in Tennessee only; Botryosphaeria dothidea, in Indiana and Tennessee; and Fusarium solani (= members of F. solani species complex), in all three states. The latter two fungi may exacerbate branch dieback and mortality of TCD-affected trees. These results will be of value to plant health specialists monitoring J. nigra in the field and laboratory diagnosticians processing survey samples.