While southern rust reports continue to come in from TN counties, the question now is – do you need to protect your corn with a fungicide application?
Fields that received a fungicide application at tassel (VT-R1) should have protection from yield loss, but those that are after tassel but before dent that did not receive a fungicide application may benefit from a fungicide application – it depends on the amount of disease and exact growth stage.
What is clear is corn that is 2 weeks from black layer (50% starch line) will not benefit from a fungicide application and an application at R5 (25% dent) will have little to no impact on protecting yield. From Dr. Travis Faske’s published multiyear research, at University of Arkansas, he has found that “applications of QoI or QoI+DMI fungicides applied at tassel provided greater disease control (52.5%) than those applied at milk (5.8%) or dent (1.4%), and greater yield protection (40.4%) than those applied at milk (23.7%) or dent (2.6%) when final southern rust development was severe (>40%). Additionally, when rust development increased later in the season (which may be the situation in some areas of TN now), after milk growth stage, a trend of better disease control was observed with fungicides applied at milk (57.8%) compared with tassel (35.2%), but grain yield protection was similar, with an average yield protection of 7.4%. There was no yield benefit with fungicides applied in the absence of disease or at the dent growth stage.” The entire article can be found here: https://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-06-20-1247-RE