Winter Survival and Source of Primary Inoculum of Powdery Mildew of Dogwood in Tennessee

Abstract

A 3-year study (1996-1998) on the epidemiology of dogwood powdery mildew showed that Microsphaera pulchra is the primary powdery mildew pathogen of dogwoods (Cornus spp.) in mid-Tennessee, and the occurrence of Phyllactinia guttata is insignificant. Cleistothecia harvested from leaf debris in spring contained viable asci and ascospores and produced powdery mildew infection on disease-free plants. Ascospores that were morphologically similar to those of M. pulchra were trapped on sticky slides in the vicinity of dogwoods throughout spring. Previously infected plants that did not harbor cleistothecia failed to develop signs of infection under growth-chamber and greenhouse conditions conducive to powdery mildew infections. Results from these studies indicate that cleistothecia on leaf debris rather than mycelia on dormant buds constitute the main winter survival structure and primary sources of spring inoculum in mid-Tennessee.