The disease cycle of fire blight caused by the bacterium Erwinia amylovora. Dashed lines represent movement of bacteria and spread of disease within the plant and solid lines represent movement of bacteria outside the plant. Modified from disease cycle of Sherman Thomson (Thomson, S.V. 2000. Epidemiology of fire blight. Pages 9-36 in: Fire blight: The disease and its causative agent, Erwinia amylovora, edited by J. Vanneste. Oxon, UK and NY, NY: CABI Publishing.). Thanks to Wilbur Hershberger for preparing the graphics. (Modified by J. Norelli, USDA, Appalachian Fruit Research Station, March 2003).