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Site-specific management of spring dead spot of bermudagrass (Cynodon spp.)

Jordan Booth: Virginia Tech

<div>Spring dead spot (SDS) is a reoccurring disease of bermudagrass (<em>Cynodon </em>spp.) in colder regions of adaptation. <em>Ophiosphaerella</em> spp. can infect prior to winter dormancy and predispose the plants to isolated patches of winter damage. Symptoms of dead patches in the turf appear in the spring and can persist for months. Fall fungicide applications have proven most effective for disease suppression. Because symptoms are not present at the time of application, current suppression tactics include multiple fungicide applications across all managed acreage. Despite inconsistent results, turfgrass managers often use affordable fungicides to control costs. Site-specific applications to areas with known SDS outbreaks may result in total fungicide reductions. Precision-guided applications have the potential to reduce costs while maintaining disease suppression. Research objectives include development of methods to map, evaluate, and quantify SDS epidemics as well as the evaluation of site-specific fungicide applications based on historical disease incidence. Aerial imagery was used to create disease maps in spring 2016 and 2017 from five bermudagrass fairways with a history of SDS. Treatments were arranged in a completely randomized design across twenty replicated 33 m<sup>2</sup> plots to include 1) untreated 2) full-coverage tebuconazole (1.2 kg ai ha<sup>-1</sup>), 3) full-coverage penthiopyrad (1.07 kg ai ha<sup>-1</sup>), and 4) site-specific penthiopyrad (1.07 kg ai ha<sup>-1</sup>.) Fall treatments were initiated when soil temperatures reached 18°C. Site-specific treatments reduced fungicide usage by 51% in 2016 and 65% in 2017 while providing statistically equivalent suppression when compared to full-coverage plots. This research demonstrates how treated fungicide acreage can be reduced by using site-specific management from SDS distribution maps without compromising efficacy.</div>