Verticillium—Induced Scorch and Chlorosis in Ash

Abstract Verticillium dahliae appears to be the causal agent of a common disorder of white and green ash that has increasingly affected nursery and landscape trees in the Upper Midwest. Affected trees are without wilting or vascular discoloration typical of Verticillium symptoms on other woody hosts, although upper branch and unilateral distribution patterns remain common and important clues. Symptoms include considerable light green to chlorotic foliage followed by irregular leaf scorch, defoliation and branch dieback. The fungus was best isolated from leaf petioles on potato dextrose agar containing 100 ppm iprodione + 200 ppm chloramphenicol. Repeated and intensive sampling was often necessary to detect the fungus. Symptom recurrence in following years was common but erratic and unpredictable. A discussion of environmental influences and control possibilities is included.