The term scorch is commonly used to describe foliar symptoms of marginal and interveinal dessication. A diversity of abiotic and biotic agents cause scorch symptoms in shade trees. Thus there are many physiologic and pathologic bases for leaf scorch. Little research has been performed to define these bases; however, recent research involving fastidious xylem-inhabiting bacteria (FXIB) in elm, sycamore, oak, and mulberry has provided some insights while raising new questions and interest about scorch in shade trees. Characteristics of scorched trees are presented which should prove useful for the often-difficult task of field differentiation of biotic from abiotic scorches.