Epiphytic populations of ice nucleation active (INA) strains of Pseudomonas syringae van Hall of up to 106cells/g fresh weight were found on healthy tissues of commercially managed almond [Prunus dulcis (Mill.) D.A. Webb] orchards in California. Leaf bacteria accounted for over 99% of the ice nuclei active at temperatures higher than − 5°C on almond. Large, seasonal variations in populations of INA bacteria and ice nuclei on almond were observed, with maximum populations found shortly after full bloom. These populations were reduced from 10- to 100-fold by 3 weekly applications of bactericides starting at budbreak, or a single application at 10% bloom of a nonice nucleation active antagonistic bacterium isolated from an almond leaf surface. Applications of cupric hydroxide to dormant tissues and/or to growing tissue after budbreak were most effective at reducing populations of INA bacteria and ice nuclei on almond. Application of bacterial ice nucleation inhibitors did not influence populations of INA bacteria on almond shoots shortly after application, but reduced the numbers of ice nuclei active at −5° or warmer. Frost injury to detached almond spurs cooled to −3° was reduced by all treatments that reduced the numbers of bacterial ice nuclei on almond tissue.