Precision Guided Applications for the Suppression of Spring Dead Spot.

Spring dead spot (SDS) is a reoccurring disease of bermudagrass (Cynodon dactylon) in regions where bermudagrass enters winter dormancy. Preventative fall fungicide applications have proven most effective at suppressing SDS, though performance is often inconsistent. Multiple fungicide applications are commonly applied across all managed acreage to maximize control. Large acreage and multiple applications lead to high cost of application. Site-specific applications to areas with known SDS outbreaks may result in total fungicide reductions. This would provide the potential for expensive fungicides to be utilized with increased effectiveness making them more economically feasible. Precision guided applications have the potential to reduce costs of control measures while increasing disease suppression with improved accuracy. The objective of this research is to investigate use of site-specific fall fungicide applications using historical SDS incidence maps of spring outbreaks. Disease maps were generated using aerial imagery collected during spring 2016 and 2017 from six ‘Vamont’ bermudagrass fairways with high SDS occurrence in Richmond, Virginia. Four treatments were arranged in a completely randomized design across twenty replicated 33 m² plots to include 1) non-treated control, 2) full-coverage tebuconazole applied at 1,236 g ai ha^-1, 3) full-coverage penthiopyrad applied at 1,068 g ai ha^-1, and 4) site-specific penthiopyrad applied at 1,068 g ai ha^-1. Treatments were applied in fall 2016 and 2017 when soil temperatures reached 18°C and again 28 days later. Fungicides were applied in 2016 to site-specific treatments exceeding a threshold of two SDS patches within each of three 11 m² subplots using an individual sprayer boom. In 2017, fungicides were applied to 1 m² site-specific units within whole-plots using individual nozzle control across thirty-three subplots. Fungicide reduction across locations averaged 51% in 2016 and currently undetermined in 2017. This research demonstrates how treated fungicide acreage can be reduced using site-specific management from SDS distribution maps.