Investigating targeted spring dead spot management via aerial mapping and precision‐guided fungicide applications

Abstract Spring dead spot ( Ophiosphaerella herpotricha, O. korrae, O. narmari ; SDS) is among the most destructive diseases of bermudagrass [ Cynodon dactylon (L.) Pers.] and hybrid bermudagrass ( C. dactylon x C. transvaalensis Burtt Davy) in the Transition Zone of the United States. Spring dead spot's primary causal agents in the United States, Ophiosphaerella korrae and O. herpotricha , infect bermudagrass in the fall with symptoms appearing in the spring when winter dormancy breaks. Patches of necrotic turfgrass often reoccur in the same location and expand into surrounding areas. Chemical control options are often expensive or provide inconsistent results. Our objectives were to develop SDS incidence maps, analyze these maps, and evaluate suppression efficacy of chemical applications guided by incidence‐based maps. Digital imagery captured with an unmanned aerial vehicle (UAV) was used to create SDS incidence maps in the spring of 2016, 2017, and 2018. In the fall of 2016 and 2017, a targeted, site‐specific penthiopyrad treatment was evaluated against blanket, full‐coverage applications of penthiopyrad and tebuconazole, and a nontreated control. Treatments were compared using digital image analysis of diseased area (DA) and post‐treatment SDS patch count (PC). Across both metrics, the penthiopyrad treatments had significantly less disease than both the tebuconazole and nontreated control in 2016–2017. Targeted penthiopyrad compared favorably to full coverage penthiopyrad for DA and PC in 2016–2017, but full‐coverage penthiopyrad was superior to targeted penthiopyrad and tebuconazole in 2017–2018 for both DA and PC. Targeted penthiopyrad using SDS incidence maps required 51% less fungicides in 2016–2017 and 65% less in 2017–2018 when compared to full‐coverage penthiopyrad.