Environmental and edaphic factors that influence spring dead spot epidemics.

Spring dead spot (SDS) (Ophiosphaerella spp.) is a soilborne disease of warm-season turfgrasses grown where winter dormancy occurs. The edaphic factors that influence where SDS epidemics occur are not well defined. A study was conducted spring of 2020 and repeated spring of 2021 on four 'TifSport' hybrid bermudagrass (Cynodon dactylon (L.) Pers. x transvaalensis Burtt Davy) golf course fairways expressing SDS symptoms in Cape Charles, VA, USA. Spring dead spot within each fairway was mapped from aerial imagery collected spring of 2019 with a 20 MP CMOS 4k true color sensor mounted on a DJI Phantom 4 Pro drone. Three disease intensity zones were designated from the maps (low, moderate, high) based on the density of SDS patches in an area. Disease incidence and severity, soil samples, surface firmness, thatch depth, and organic matter measurements were taken from ten plots within each disease intensity zone from each of the four fairways (n=120). Multivariate pairwise correlation analyses (P < 0.1) and best subset stepwise regression analyses were conducted to determine which edaphic factors most influenced the SDS epidemic within each fairway and each year. Edaphic factors that correlated with an increase in SDS or were selected for the best fitting model varied across holes and years. However, in certain cases, soil pH and thatch depth were predictors for an increase in SDS. No factors were consistently associated with SDS occurrence, but results from this foundational study of SDS epidemics can guide future research on correlating factors that may drive disease development.