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Southern rust (Puccinia polysora) is a fungal disease that generally affects corn later in the season after silking. Southern rust may lead to reduced photosynthesis during grain fill, which can reduce levels of carbohydrates to stalks and roots due to the demand to fill ears. Corn products can vary in susceptibility to the disease. Fungicides can be applied to help prevent the spread of southern rust. Research that has been conducted in the South has focused on yield response to fungicides applied only at tassel (VT) growth stage. Southern rust severity will vary from year to year depending on environmental conditions. A study was established to help farmers maximize profitability in a systems approach to disease management using both genetics and fungicides.
The objective of this study was to assess the impact of fungicide timings on disease severity, yield, profitability, and harvest intactness on corn products that vary in susceptibility to southern rust.
Table 1. Product ratings for Southern rust and gray leaf spot (GLS).Rating scale: 1=excellent; 9=poor.
Figure 1. Average increase in corn yield with fungicide application at different timings as compared to no fungicide application in 2017.
Figure 2. Average southern rust severity rating taken at the R4 growth stage.
Table 2. Return on investment (ROI) for each fungicide application timing and corn product tolerance. ROI calculated based on a corn price of $3.50/bu and fungicide application cost of $35/acre.