A proposed winter-injury classification for apple trees on the northern fringe of commercial production

Abstract

Because of a severe and highly variable winter environment, commercially significant fruit production in New Brunswick is restricted to a few hardy apple cultivars. Cluster, principal-component and discriminant analyses were applied to monthly temperature records to derive a satisfactory classification of recorded occurrences of winter injury in New Brunswick during the 20th century. Production of a dendrogram based on a hierarchical, agglomerative clustering technique separated root- from shoot-injury years. The analyses suggested that low temperatures per se in December, January or February are not the dominant factors controlling recurring winter shoot injury of apple trees in New Brunswick. Rather mild weather during mid-winter (especially maximum air temperature in February) and the October mean air temperature during the fall hardening-off period consistently contributed to the hierarchical classification. Cluster analysis allowed the separation of recorded occurrences of winter injury into plausible groupings that should complement current attempts to understand the underlying causes of winter injury in New Brunswick.Key words: Malus × domestica, apple, winter injury, cluster analysis