Four isolates of Bacillus spp. were tested in a 2-year field study for biological control of pre- and postharvest diseases of apple. For the preharvest test, bacteria were applied to 'Golden Delicious' and 'Rome Beauty' trees in May or May and June. Foliar apple scab severity was assessed weekly. After harvest, fruit were wounded and then either left untreated or given a postharvest application of the bacteria. Wounded fruit were then inoculated with the bitter rot pathogen and lesion size was measured over 8 days. Bacillus megaterium isolate A3-6, B. mycoides isolate A1-1, and B. cereus isolate FLS-5 applied in May or May and June significantly reduced fruit and foliar apple scab severity in both years. A postharvest application of the bacteria (alone or in combination with a preharvest application) resulted in the greatest suppression of bitter rot on both cultivars (P < 0.04). The May + June + postharvest application of isolate A3-6 resulted in the greatest suppression of bitter rot, with an average of 45 and 95% reduction in lesion size compared with nontreated controls on 'Golden Delicious' and 'Rome Beauty' fruit, respectively. Results from this study indicate that preharvest applications of the bacteria were able to reduce foliar and fruit scab and an additional postharvest application was effective in reducing bitter rot severity.