Sodium bicarbonate (SBC) effectively inhibited spore germination and germ tube elongation of Venturia inaequalis in vitro. SBC at 0.5%, 1%, and 2% inhibited spore germination by 59.0%, 96.4%, and 100%, respectively. In two orchard experiments to investigate the efficacy of SBC alone or in combination with a reduced dose of tebuconazole in inhibiting apple scab, applications of 1% SBC to trees at 10-d intervals significantly reduced disease incidence and severity on leaves and fruit compared to the water-treated control. In the first experiment, by the last assessment, the 1% SBC treatment had reduced the disease incidence on leaves to 29.6% compared with 62.6% in the water-treated control. The efficacy of 1% SBC was comparable with that of the label dose of tebuconazole on leaves and fruit. Combining 1% SBC with a reduced dose (10% of label dose) of tebuconazole did not improve the efficacy of 1% SBC alone. Treatments of 2% SBC were phytotoxic to leaves, but 1% SBC was neither phytotoxic to leaves nor did it adversely affect quality parameters of harvested fruit. (c) 2006 Elsevier Ltd. All rights reserved.