Phylloplane microorganism survival is presumably affected by ultraviolet radiation (UV) penetrating into plant canopies, but little field data exist relating microorganism population dynamics to canopy UV level. Recent advances in field measurements involving the use of biological dosimeters and miniature radiometers make possible data sets for use in assessing the impact of UV on phylloplane microbe survival. The objective of this study was to compare field survival of a bacterial species, applied to turfgrass as a biological disease control agent, with predicted survival based on the prevailing UV-B environment under natural and attenuated UV conditions. Derived survival curves and radiation penetration equations (based on radiometer and biodosimeter field measurements of UV-B transmittance) were applied to predict bacterial survival within a turfgrass canopy at different leaf area indices. Due to the range in UV levels within a canopy, as indicated by the maximum (sunfleck areas) and minimum (shaded areas) transmitted irradiance values, bacterial survival can vary; predicted bacterial survival based only on average light penetration tended to underestimate survival. Further study should address contributions due to microenvironmental effects (e.g., canopy temperature, leaf wetness, and canopy structure), the spatial distribution of bacterium leaf microsites and bacterium survival on leaf surfaces.