Sapstreak disease is a potentially serious problem of sugarbushes and forest stands. It is caused by the fungus Ceratocystis virescens, which invades sapwood of roots and bases of stems through wounds created during logging, saphauling, or other activities. This report describes the results of observations and experiments to learn more about the patterns of disease development and the factors that affect them, within individual trees and within representative forests and sugarbushes.