OBSERVATIONS ON APPLE CANKER

Field observations on leaf‐scar canker of apple confirm its importance in the southwest of England: on a heavily infected tree more than 5% of the current year's growth may be damaged. Leaf scars may become infected by spores of Nectria galligena which are sucked into the tracheids of a freshly exposed scar where they develop in a relatively protected environment. These freshly exposed scars become much less susceptible to infection after approximately one hour. Infections established in leaf scars may develop immediately into cankers or they may be confined by a suberized or gum barrier. Mycelium from some of these confined lesions may spread into the surrounding healthy tissue through growth cracks when the buds develop. The lesions extend throughout the winter and spring; usually the scars earliest inoculated are the first to show cankers. It seems possible that infections of this type might be controlled by eradicant sprays applied just before leaf‐fall.