Predictive Equations for Local Spread of Oak Wilt in Southern Wisconsin

Oak wilt, caused by the fungus Ceratocystis fagacearum , is an important vascular wilt disease of oaks in the United States. In some areas, the pathogen spreads among adjacent trees of the red oak group through natural root grafts. Mapped data on oak wilt mortality were analyzed to predict probabilities of local spread between pairs of susceptible trees. Such probabilities were best predicted by the combined diameters at breast height ( CDBH ) and the intertree distance ( D ) as CDBH/D or CDBH - D . Regressions predicting transmission probability differed in slope between sites. But slopes were similar for tree-to-tree spread of different durations within sites, confirming that time for spread is not related to tree size or intertree distance. These relationships may be used to determine which trees in a woodlot or urban planting are in greatest danger of local transmission of oak wilt. They indicate where physical or chemical barriers to root-graft transmission should be placed. Forest Sci. 31:43-51.