Ecological Status of Juglans cinerea in New Brunswick

Butternut (Juglans cinerea L.), an early successional riparian hardwood species native to Canada and the United States, is under serious threat from a nonnative fungal pathogen, Ophiognomonia clavigignenti-juglandacearum. Since it was first reported in Canada in 1990, this fungal pathogen has spread rapidly and established in New Brunswick in 1997. Apart from the first report in 1997 and another in 2004, no surveys have been conducted to assess the spread of the pathogen in the province. The purpose of this research was to survey butternut throughout its range in New Brunswick, evaluate disease occurrence as well as tree health, and investigate the impact of different topographic and tree health factors on canker incidence. Results showed that the disease has spread throughout the range of butternut in New Brunswick. The disease likely only recently (2007) spread to the northeastern-most populations, given that lower rates of canker occurrence and higher health ratings are found further away from the point of initial occurrence of the disease. Although canker incidence is high throughout the province, tree dieback is minimal, and trees still producing nuts could support opportunities for ex situ conservation. Because of the rate of pathogen spread in the province, implementing a tree improvement strategy might be the only means for maintaining the butternut genome on the landscape.