Erwinia amylovorainfection of either apple stem or leaf tissue resulted in xylem occlusion by a fibrillar matrix material, determined by Thiery’ s thiocarbohydrazide (TCH) test to be the extracellular polysaccharide fromE. amylovora.Plasmolysis of the xylem‐parenchyma was also detected and was most likely a result of a toxin produced by the pathogen. This plasmolysis resulted in the collapse and death of the cell. AnErwinia herbicolaisolate which had previously expressed inhibitory effects onE. amylovorawas contained at the site of inoculation.