Dead spot severity, pseudothecia development, and overwintering of Ophiosphaerella agrostis in creeping bentgrass

Dead spot (Ophiosphaerella agrostis) is a damaging disease of young (≤6 years old) creeping bentgrass (Agrostis stolonifera) golf greens. The objectives of this 3-year field study were to determine the peak periods of dead spot activity based on increasing patch diameter and pseudothecia development, and to determine where O. agrostis overwinters. Patch diameter generally increased at a linear rate between mid-June and early August. Increases in pseudothecia production closely followed increasing patch diameter. Pseudothecia could be found within necrotic tissue as early as the first day of symptom expression and as many as 478 pseudothecia were found in a single patch. Periods of rapid dead spot development coincided with air and soil temperatures ranging from 22 to 26°C. Increases in patch diameter and pseudothecia development were negligible after late August. Dead spot severity was highest in the year following green construction or fumigation, but then rapidly declined in severity in subsequent years. O. agrostis was capable of overwintering as pseudothecia or as hyphae within or on bentgrass leaf sheaths, crowns, roots, and especially the nodes of stolons.