Evaluation of Thousand Cankers Disease-Symptomatic Juglans nigra in Southwestern Ohio Following Population Collapse of Pityophthorus juglandis

Abstract

Mass attacks of Juglans nigra by Pityophthorus juglandis and its introduction of the canker pathogen Geosmithia morbida lead to branch dieback and, commonly, tree death in locations with outbreaks of thousand cankers disease (TCD). Following initial detection of TCD in Butler County, Ohio, in 2012, and trapping of thousands of P. juglandis, a dramatic decrease in insect population occurred. Dissections of “lingering” TCD-symptomatic J. nigra in 2014 and 2015 were conducted to document the presence of “typical” Geosmithia cankers and other types of damage on branches and main stems. Isolation and subsequent molecular identification of G. morbida and other selected fungi were attempted from representatives of the various canker-like and insect-associated damage observed. Of the fungi obtained, G. morbida was most commonly isolated, primarily from “typical” Geosmithia cankers, but it was also obtained at lower frequencies from other damage types. In addition, G. morbida commonly co-occurred with Fusarium solani ( F. solani species complex) but infrequently with Diplodia seriata. These other fungal species could contribute to the severity of canker development. These results suggest that the TCD pathogen persists in the landscape following population collapse of the primary insect vector and would be of interest to state regulatory agencies in the eastern United States.