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The yield response and reaction of selected mid- and full-season commercial cotton varieties to target spot, incited by Corynespora cassiicola, as influenced by fungicide inputs was conducted at the Brewton Agriculture Research Unit (BARU) in 2014, 2015, and 2016. The experimental design was a factorial set of treatments arranged in a split plot, with the varieties Phytogen 499 WRF, Phytogen 575 WRF, Deltapine 1137 B2RF, Deltapine 1252 B2RF, Fibermax 1944 GLB2, and Stoneville 6448 GLB2 as whole plots and an umbrella fungicide program consisting of four or five applications of Headline SC at 9 fl oz/A + Bravo Ultrex at 1.5 pt/A to minimize disease activity and yield loss. The site was irrigated as needed and managed for maximum yield. Final % defoliation and relative area under the disease progress curve (rAUC) for defoliation differed by variety and fungicide program. While final % defoliation and rAUC for all the above varieties were lower for the fungicide- than non-fungicide treated controls, lower values for the above variables were obtained for the fungicide-treated Phytogen 575 WRF, Deltapine 1252 B2RF, Stoneville 6448 GLB2, and Fibermax 1944 GLB2 than Phytogen 499 WRF, which suffered the greatest disease-related defoliation. For the non-fungicide treated controls, higher defoliation and rAUC values were obtained for the latter than for the other five remaining varieties, which had similarly lower values for both target spot variables. Over the study period, equally higher yields were noted in 2014 and 2015 than 2016, when elevated hard lock counts were linked with sharply lower yields. In addition, Fibermax 1944 GLB2 and Deltapine 1252 B2RF had higher lint yields than Phytogen 575 WRF, Deltapine 1137 B2RF, and Stoneville 6448 GLB2 but not Phytogen 499 WRF with all of the latter varieties having similar yields. Finally, greater lint yields were noted for the fungicide- than non-fungicide treated controls. While higher open boll counts were recorded in 2014 than either of the following two study years, hardlock boll counts progressively increased each study year from a low of 2.4 in 2014 to 11.7 in 2016. Rotted boll counts were higher in 2015 and 2016 than in 2014. For 2015, counts of rotted bolls was higher for the fungicide-treated than non-fungicide treated control with the latter treatment having similar rotted boll counts as the fungicide-treated and non-fungicide treated control in 2016.
Complete report can be viewed at2017 Cotton Target Spot Varieties Timely Information.rev.pdf
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