Target Spot-Incited Defoliation and Yields of Selected Cotton Cultivars as Influenced by Fungicide Inputs

Abstract

Target spot, caused by Corynespora cassiicola, prematurely defoliates and occasionally reduces cotton yield across the southeastern United States. Reaction of the cultivars Deltapine 1137 B2RF, Deltapine 1252 B2RF, Fibermax 1944 GLB2, PhytoGen 499 WRF, PhytoGen 575 WRF, and Stoneville 6448 GLB2 to target spot and lint yield as influenced by a full-season Headline + Bravo Ultrex fungicide program was assessed for 3 years in southwest Alabama. Significantly greater final % and relative area under the disease curve (relAUC) season-long defoliation was recorded for PhytoGen 499 WRF than the other cultivars, which had similarly lower defoliation values. A significant yield gain of 92 kg of lint/ha valued at $142/ha across all cultivars was obtained with the fungicide program. In addition, PhytoGen 499 WRF and Fibermax 1944 GLB2 had significantly lower defoliation and greater yield gains (189 and 263 kg of lint/ha, respectively) with the fungicide than no fungicide program. Hardlock incidence was greater in 2016 than in preceding years and did not differ by fungicide program. Open and unopen boll counts were similar across all cultivars and fungicide programs. Study results indicate that partially resistant cultivars may be an effective tool for managing target spot in cotton.