Influence of post-application irrigation and soil surfactants on tebuconazole efficacy against spring dead spot

Spring dead spot (SDS) (Ophiosphaerella spp.) causes damage to hybrid bermudagrass (Cynodon dactylon (L.) Pers. x transvaalensis Burtt Davy) grown in areas where winter dormancy occurs. The pathogen infects the stolons, rhizomes, and roots of warm-season grasses. Symptoms appear as circular, necrotic patches at spring greenup that reduce the playability and aesthetics of bermudagrass. Historically, fungicide efficacy against SDS has been inconsistent. There may be opportunities to improve application and post-application practices to mitigate the inconsistency. A study was conducted from 2019 to 2021 to examine the influence of post-application irrigation and soil surfactant on tebuconazole efficacy against SDS. The study was conducted at three locations: Virginia Tech Turfgrass Research Center (TRC), Blacksburg, VA; Independence Golf Club (IGC), Midlothian, VA; Nutters Crossing Golf Club (NCGC), Salisbury, MD. Tebuconazole was applied in the fall either once at 1.5 kg ai ha⁻¹ or twice at 1.5 kg ai ha⁻¹ two to four weeks apart when soil temperatures were between 10.7 and 21.8 °C. Treatments were applied with or without a soil surfactant and with or without 0.6 cm of post-application irrigation. Bermudagrass was assessed the following spring two or three times for patch number and percent SDS. Data were analyzed by assessment date, subjected to analysis of variance, and means were separated using Tukey's Honest Significant Difference test (P = 0.05). There were no treatment differences at IGC or NCGC in 2020 or 2021. At the TRC in both 2020 and 2021, results were inconsistent with tebuconazole generally suppressing SDS compared to the nontreated control. However, differences between tebuconazole-treated plots were variable. Our study suggests that including a soil surfactant with tebuconazole applications and/or irrigating post-application does not consistently increase SDS suppression.