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Spatial Correlations of Southern Rust and Soil Phosphorus in Corn

Justin Bailey: University of Arkansas-Fayetteville

<div>Southern rust (SR), caused by the fungus <em>Puccinia polysora</em>, is an economically important corn disease in Arkansas. Due to rapid reproduction by the fungus, its initial identification causes concern for growers. Additionally, scouting and proper fungicide timing can be difficult because farmers typically do not pay a corn scout. Therefore, it would be beneficial to determine a predictive scouting regime for SR. In 2017, four fields were found to have SR at various growth stages. Fields were spatially marked with a GPS unit at 100, 100, 80 and 73 points near Grady, Pickens, Plumerville, and Long Lake, respectively. The fields were rated for SR at detection and then every two weeks after until crop maturity. Ratings were assigned for each GPS point (within 3 meters of a single row) below the ear leaf, at the ear leaf, and above the ear leaf. Spatial distributions and relationships were determined using Moran’s I and spatial regression models. After harvest, soil samples were taken at each GPS point and processed at the University of Arkansas Soil Testing Laboratory using the Melich-3 method. Spatial analyses indicated SR spread in an aggregated pattern (P=0.05). Phosphorus levels (P) within fields varied and were also aggregated (P=0.05). Positive spatial correlations existed across all fields between SR and P (P=0.10) indicating that differences in SR severity could be controlled by plant growth and P could be a component of a SR predictive model.</div>