Technical Abstract: Fire blight of apple and pear is initiated mainly by epiphytic populations of Erwinia amylovora on flower stigmas. Understanding bacterial colonization on stigmas is relevant to disease risk assessment and biological management. When detached crab apple flowers were subjected to various temperatures and incubation periods before inoculation, maximum age of stigmas supporting bacterial multiplication decreased as temperature increased, and was reduced slightly by pollination. This was confirmed with mature Gala apple trees enclosed in polyethylene and maintained at two different temperature ranges. Depending on these variables and bacterial strain, stigma conduciveness to bacterial growth lasted 3 to 12 days. For E. amylovora, this period corresponded to the interval when stigma papillae were bulbous in scanning electron micrographs. The study revealed attributes and limitations of antagonist strains currently being exploited for fire blight management. Antagonist Pseudomonas fluorescens strain A506 failed to multiply under certain conditions favorable for the pathogen, i.e when temperatures were relatively high or stigmas old. Other antagonists, Pantoea agglomerans strains C9-1 and E325, however, grew under such conditions. Dual inoculations affirmed that efficacy of these antagonists in preemptively excluding E. amylovora is relatively constant throughout stigma development and senescence stages suitable for pathogen growth.