Dieback Disease of Pines with Special Reference to Corsican Pine Pinus nigra var. Calabrica Schn.

Abstract

The winter frost hardiness level of Corsican Pine buds in northern England is found to range from −16° C to −20 C (+3° F to −4° F). Buds in the lower parts of the tree are more susceptible to frost damage than those nearer the leader, and buds at a given position in the canopy on a north-facing slope are less hardy than those in a corresponding position on a tree in a south aspect. The symptoms produced by artificial freezing are distinct from those found in dieback disease, and temperature measurements in diseased and healthy stands suggest that frosts are not severe enough to account for the disease. The lower hardiness levels in disease susceptible areas are therefore considered to be of secondary importance and are probably a result of a weakened physiological condition in the tree. Diseased slopes are chiefly characterized by high humidities, low light intensities, and only slightly reduced air and soil temperatures when compared with nearby healthy areas.