Disease Control and Yield Response of a Target Spot Susceptible and Partially Resistant Cultivar As Influenced By Fungicide Inputs over a Three Year Period

Efficacy of registered fungicides for target control on the susceptible PhytoGen 499WRF and several partially Deltapine resistant cotton varieties was evaluated in southwest AL. A factorial arranged in a split-split plot with year as the whole plot, cotton variety resistance as the split plot, and fungicide program as the split-split plot was used. While the partially resistant varieties Deltapine 1050 B2RF, Deltapine 1252 B2RF, and Deltapine 1137 B2RF were produced in 2012, 2013, and 2016, respectively, the target spot susceptible variety PhytoGen 499 WRF was sown in all study years. Fungicide programs consisted of two applications of Headline 2.09SC at 6 and 9 fl oz/A, Quadris 2.08SC at 6 and 9 fl oz/A, or Twinline at 7 and 8.5 fl oz/A along with a non-fungicide treated control. When compared with Deltapine 1050 B2RF in 2012, less defoliation was noted for Deltapine 1252 B2RF and Deltapine 1137 B2RF in 2013 and 2016, respectively. Less final % defoliation was observed for the fungicide-treated cotton than the non-fungicide treated control with Headline at 9 fl oz/A proving more efficacious against target spot than both rates of Quadris. Over the study period, defoliation was lower for the Headline, Quadris, and Twinline-treated cotton than the non-fungicide treated control with the Headline at 9 fl oz/A proving more efficacious than both rates of Quadris against target spot. Application rate did not influence disease control with any fungicide. Significant year × variety and variety × fungicide program interactions for seed yield were noted. While the seed yield for PhytoGen 499 WRF was similar to Deltapine 1050 B2RF and Deltapine 1137 B2RF in 2012 and 2016, respectively, Deltapine 1252 B2RF produced higher seed yields than PhytoGen 499 WRF in 2013. Seed yield for PhytoGen 499 WRF as well as the three Deltapine varieties differed by study year.