Timing of Perennial Canker Development in Apple Trees Caused by Neofabraea perennans and Neofabraea kienholzii.

Members of the genera Neofabraea and Phlyctema have been reported to incite canker diseases of apple trees and a postharvest decay of apple fruit referred to as "bull's-eye rot." Neofabraea kienholzii was recently identified as participating in the bull's-eye rot disease complex of apple and other pome fruit. In this study, apple twigs inoculated with N. kienholzii were shown to develop symptoms of a canker disease closely resembling perennial canker of pome fruit trees caused by N. perennans. Cankers resulting from infection by either Neofabraea spp. were more likely to be induced when twig inoculations occurred in October, and to a lesser degree in April, compared with all other inoculation dates evaluated in this study. Although N. kienholzii tended to induce cankers that were smaller in size compared with N. perennans, both pathogens shared similar seasonal trends in the initiation and expansion of tree cankers. N. perennans and N. kienholzii were recovered from inoculated twigs 6 months postinoculation regardless of when inoculations were conducted, indicating that both pathogens can survive on diseased twigs year-round. In addition, acervuli were observed more often on twigs inoculated in September and April compared with those inoculated in other months. Data from this work should help further our understanding of the epidemiology of N. kienholzii. This information also highlights the importance of proper branch pruning, canker removal, and aphid control. Such management activities should be conducted in a manner that helps minimize further spread of the pathogen.