Fungal immigration to apple leaves in the field was altered by the introduction of populations of Chaetomium globosum or Aureobasidium pullulans to surface-disinfested leaves either immediately following, or 6 days after, disinfestation. Total numbers of fungal individuals and numbers of filamentous fungal and yeast individuals were estimated and compared over time for 4-7 weeks on control leaves (leaves disinfested but no populations applied), on Aureobasidium-treated, and on Chaetomium-treated leaves. Fungal communities developing on leaves during three experiments in two different time frames (experiment 1: July 9-August 27; experiments 2 and 3: July 29-August 27), and thus under different immigration regimes, were also compared. Survival of introduced populations was not related to the presence of prior fungal immigrants. Rates of increase in total numbers of fungi and numbers of filamentous fungi and yeasts per leaf varied among experiments, apparently in relation to differences in immigration and environmental history. Differences among leaves in immigration had a short-term (days) influence on community size. However, no long-term effects of altered immigration on phylloplane fungal community size were evident.